Add HashMap and HashSet

11 files changed, 6297 insertions, 5 deletions

diff --git a/ctr-std/src/collections/hash/bench.rs b/ctr-std/src/collections/hash/bench.rs
new file mode 100644
index 0000000..ff6cb79
--- /dev/null
+++ b/ctr-std/src/collections/hash/bench.rs
@@ -0,0 +1,128 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![cfg(test)]
+
+extern crate test;
+
+use self::test::Bencher;
+
+#[bench]
+fn new_drop(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    b.iter(|| {
+        let m: HashMap<i32, i32> = HashMap::new();
+        assert_eq!(m.len(), 0);
+    })
+}
+
+#[bench]
+fn new_insert_drop(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    b.iter(|| {
+        let mut m = HashMap::new();
+        m.insert(0, 0);
+        assert_eq!(m.len(), 1);
+    })
+}
+
+#[bench]
+fn grow_by_insertion(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    let mut m = HashMap::new();
+
+    for i in 1..1001 {
+        m.insert(i, i);
+    }
+
+    let mut k = 1001;
+
+    b.iter(|| {
+        m.insert(k, k);
+        k += 1;
+    });
+}
+
+#[bench]
+fn find_existing(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    let mut m = HashMap::new();
+
+    for i in 1..1001 {
+        m.insert(i, i);
+    }
+
+    b.iter(|| {
+        for i in 1..1001 {
+            m.contains_key(&i);
+        }
+    });
+}
+
+#[bench]
+fn find_nonexisting(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    let mut m = HashMap::new();
+
+    for i in 1..1001 {
+        m.insert(i, i);
+    }
+
+    b.iter(|| {
+        for i in 1001..2001 {
+            m.contains_key(&i);
+        }
+    });
+}
+
+#[bench]
+fn hashmap_as_queue(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    let mut m = HashMap::new();
+
+    for i in 1..1001 {
+        m.insert(i, i);
+    }
+
+    let mut k = 1;
+
+    b.iter(|| {
+        m.remove(&k);
+        m.insert(k + 1000, k + 1000);
+        k += 1;
+    });
+}
+
+#[bench]
+fn get_remove_insert(b: &mut Bencher) {
+    use super::map::HashMap;
+
+    let mut m = HashMap::new();
+
+    for i in 1..1001 {
+        m.insert(i, i);
+    }
+
+    let mut k = 1;
+
+    b.iter(|| {
+        m.get(&(k + 400));
+        m.get(&(k + 2000));
+        m.remove(&k);
+        m.insert(k + 1000, k + 1000);
+        k += 1;
+    })
+}
diff --git a/ctr-std/src/collections/hash/map.rs b/ctr-std/src/collections/hash/map.rs
new file mode 100644
index 0000000..0b310eb
--- /dev/null
+++ b/ctr-std/src/collections/hash/map.rs
@@ -0,0 +1,3073 @@
+// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use self::Entry::*;
+use self::VacantEntryState::*;
+
+use cell::Cell;
+use borrow::Borrow;
+use cmp::max;
+use fmt::{self, Debug};
+#[allow(deprecated)]
+use hash::{Hash, Hasher, BuildHasher, SipHasher13};
+use iter::{FromIterator, FusedIterator};
+use mem::{self, replace};
+use ops::{Deref, Index};
+use rand::{self, Rng};
+
+use super::table::{self, Bucket, EmptyBucket, FullBucket, FullBucketMut, RawTable, SafeHash};
+use super::table::BucketState::{Empty, Full};
+
+const MIN_NONZERO_RAW_CAPACITY: usize = 32;     // must be a power of two
+
+/// The default behavior of HashMap implements a maximum load factor of 90.9%.
+#[derive(Clone)]
+struct DefaultResizePolicy;
+
+impl DefaultResizePolicy {
+    fn new() -> DefaultResizePolicy {
+        DefaultResizePolicy
+    }
+
+    /// A hash map's "capacity" is the number of elements it can hold without
+    /// being resized. Its "raw capacity" is the number of slots required to
+    /// provide that capacity, accounting for maximum loading. The raw capacity
+    /// is always zero or a power of two.
+    #[inline]
+    fn raw_capacity(&self, len: usize) -> usize {
+        if len == 0 {
+            0
+        } else {
+            // 1. Account for loading: `raw_capacity >= len * 1.1`.
+            // 2. Ensure it is a power of two.
+            // 3. Ensure it is at least the minimum size.
+            let mut raw_cap = len * 11 / 10;
+            assert!(raw_cap >= len, "raw_cap overflow");
+            raw_cap = raw_cap.checked_next_power_of_two().expect("raw_capacity overflow");
+            raw_cap = max(MIN_NONZERO_RAW_CAPACITY, raw_cap);
+            raw_cap
+        }
+    }
+
+    /// The capacity of the given raw capacity.
+    #[inline]
+    fn capacity(&self, raw_cap: usize) -> usize {
+        // This doesn't have to be checked for overflow since allocation size
+        // in bytes will overflow earlier than multiplication by 10.
+        //
+        // As per https://github.com/rust-lang/rust/pull/30991 this is updated
+        // to be: (raw_cap * den + den - 1) / num
+        (raw_cap * 10 + 10 - 1) / 11
+    }
+}
+
+// The main performance trick in this hashmap is called Robin Hood Hashing.
+// It gains its excellent performance from one essential operation:
+//
+//    If an insertion collides with an existing element, and that element's
+//    "probe distance" (how far away the element is from its ideal location)
+//    is higher than how far we've already probed, swap the elements.
+//
+// This massively lowers variance in probe distance, and allows us to get very
+// high load factors with good performance. The 90% load factor I use is rather
+// conservative.
+//
+// > Why a load factor of approximately 90%?
+//
+// In general, all the distances to initial buckets will converge on the mean.
+// At a load factor of α, the odds of finding the target bucket after k
+// probes is approximately 1-α^k. If we set this equal to 50% (since we converge
+// on the mean) and set k=8 (64-byte cache line / 8-byte hash), α=0.92. I round
+// this down to make the math easier on the CPU and avoid its FPU.
+// Since on average we start the probing in the middle of a cache line, this
+// strategy pulls in two cache lines of hashes on every lookup. I think that's
+// pretty good, but if you want to trade off some space, it could go down to one
+// cache line on average with an α of 0.84.
+//
+// > Wait, what? Where did you get 1-α^k from?
+//
+// On the first probe, your odds of a collision with an existing element is α.
+// The odds of doing this twice in a row is approximately α^2. For three times,
+// α^3, etc. Therefore, the odds of colliding k times is α^k. The odds of NOT
+// colliding after k tries is 1-α^k.
+//
+// The paper from 1986 cited below mentions an implementation which keeps track
+// of the distance-to-initial-bucket histogram. This approach is not suitable
+// for modern architectures because it requires maintaining an internal data
+// structure. This allows very good first guesses, but we are most concerned
+// with guessing entire cache lines, not individual indexes. Furthermore, array
+// accesses are no longer linear and in one direction, as we have now. There
+// is also memory and cache pressure that this would entail that would be very
+// difficult to properly see in a microbenchmark.
+//
+// ## Future Improvements (FIXME!)
+//
+// Allow the load factor to be changed dynamically and/or at initialization.
+//
+// Also, would it be possible for us to reuse storage when growing the
+// underlying table? This is exactly the use case for 'realloc', and may
+// be worth exploring.
+//
+// ## Future Optimizations (FIXME!)
+//
+// Another possible design choice that I made without any real reason is
+// parameterizing the raw table over keys and values. Technically, all we need
+// is the size and alignment of keys and values, and the code should be just as
+// efficient (well, we might need one for power-of-two size and one for not...).
+// This has the potential to reduce code bloat in rust executables, without
+// really losing anything except 4 words (key size, key alignment, val size,
+// val alignment) which can be passed in to every call of a `RawTable` function.
+// This would definitely be an avenue worth exploring if people start complaining
+// about the size of rust executables.
+//
+// Annotate exceedingly likely branches in `table::make_hash`
+// and `search_hashed` to reduce instruction cache pressure
+// and mispredictions once it becomes possible (blocked on issue #11092).
+//
+// Shrinking the table could simply reallocate in place after moving buckets
+// to the first half.
+//
+// The growth algorithm (fragment of the Proof of Correctness)
+// --------------------
+//
+// The growth algorithm is basically a fast path of the naive reinsertion-
+// during-resize algorithm. Other paths should never be taken.
+//
+// Consider growing a robin hood hashtable of capacity n. Normally, we do this
+// by allocating a new table of capacity `2n`, and then individually reinsert
+// each element in the old table into the new one. This guarantees that the
+// new table is a valid robin hood hashtable with all the desired statistical
+// properties. Remark that the order we reinsert the elements in should not
+// matter. For simplicity and efficiency, we will consider only linear
+// reinsertions, which consist of reinserting all elements in the old table
+// into the new one by increasing order of index. However we will not be
+// starting our reinsertions from index 0 in general. If we start from index
+// i, for the purpose of reinsertion we will consider all elements with real
+// index j < i to have virtual index n + j.
+//
+// Our hash generation scheme consists of generating a 64-bit hash and
+// truncating the most significant bits. When moving to the new table, we
+// simply introduce a new bit to the front of the hash. Therefore, if an
+// elements has ideal index i in the old table, it can have one of two ideal
+// locations in the new table. If the new bit is 0, then the new ideal index
+// is i. If the new bit is 1, then the new ideal index is n + i. Intuitively,
+// we are producing two independent tables of size n, and for each element we
+// independently choose which table to insert it into with equal probability.
+// However the rather than wrapping around themselves on overflowing their
+// indexes, the first table overflows into the first, and the first into the
+// second. Visually, our new table will look something like:
+//
+// [yy_xxx_xxxx_xxx|xx_yyy_yyyy_yyy]
+//
+// Where x's are elements inserted into the first table, y's are elements
+// inserted into the second, and _'s are empty sections. We now define a few
+// key concepts that we will use later. Note that this is a very abstract
+// perspective of the table. A real resized table would be at least half
+// empty.
+//
+// Theorem: A linear robin hood reinsertion from the first ideal element
+// produces identical results to a linear naive reinsertion from the same
+// element.
+//
+// FIXME(Gankro, pczarn): review the proof and put it all in a separate README.md
+
+/// A hash map implementation which uses linear probing with Robin Hood bucket
+/// stealing.
+///
+/// By default, `HashMap` uses a hashing algorithm selected to provide
+/// resistance against HashDoS attacks. The algorithm is randomly seeded, and a
+/// reasonable best-effort is made to generate this seed from a high quality,
+/// secure source of randomness provided by the host without blocking the
+/// program. Because of this, the randomness of the seed is dependant on the
+/// quality of the system's random number generator at the time it is created.
+/// In particular, seeds generated when the system's entropy pool is abnormally
+/// low such as during system boot may be of a lower quality.
+///
+/// The default hashing algorithm is currently SipHash 1-3, though this is
+/// subject to change at any point in the future. While its performance is very
+/// competitive for medium sized keys, other hashing algorithms will outperform
+/// it for small keys such as integers as well as large keys such as long
+/// strings, though those algorithms will typically *not* protect against
+/// attacks such as HashDoS.
+///
+/// The hashing algorithm can be replaced on a per-`HashMap` basis using the
+/// `HashMap::default`, `HashMap::with_hasher`, and
+/// `HashMap::with_capacity_and_hasher` methods. Many alternative algorithms
+/// are available on crates.io, such as the `fnv` crate.
+///
+/// It is required that the keys implement the [`Eq`] and [`Hash`] traits, although
+/// this can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`.
+/// If you implement these yourself, it is important that the following
+/// property holds:
+///
+/// ```text
+/// k1 == k2 -> hash(k1) == hash(k2)
+/// ```
+///
+/// In other words, if two keys are equal, their hashes must be equal.
+///
+/// It is a logic error for a key to be modified in such a way that the key's
+/// hash, as determined by the [`Hash`] trait, or its equality, as determined by
+/// the [`Eq`] trait, changes while it is in the map. This is normally only
+/// possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
+///
+/// Relevant papers/articles:
+///
+/// 1. Pedro Celis. ["Robin Hood Hashing"](https://cs.uwaterloo.ca/research/tr/1986/CS-86-14.pdf)
+/// 2. Emmanuel Goossaert. ["Robin Hood
+///    hashing"](http://codecapsule.com/2013/11/11/robin-hood-hashing/)
+/// 3. Emmanuel Goossaert. ["Robin Hood hashing: backward shift
+///    deletion"](http://codecapsule.com/2013/11/17/robin-hood-hashing-backward-shift-deletion/)
+///
+/// # Examples
+///
+/// ```
+/// use std::collections::HashMap;
+///
+/// // type inference lets us omit an explicit type signature (which
+/// // would be `HashMap<&str, &str>` in this example).
+/// let mut book_reviews = HashMap::new();
+///
+/// // review some books.
+/// book_reviews.insert("Adventures of Huckleberry Finn",    "My favorite book.");
+/// book_reviews.insert("Grimms' Fairy Tales",               "Masterpiece.");
+/// book_reviews.insert("Pride and Prejudice",               "Very enjoyable.");
+/// book_reviews.insert("The Adventures of Sherlock Holmes", "Eye lyked it alot.");
+///
+/// // check for a specific one.
+/// if !book_reviews.contains_key("Les Misérables") {
+///     println!("We've got {} reviews, but Les Misérables ain't one.",
+///              book_reviews.len());
+/// }
+///
+/// // oops, this review has a lot of spelling mistakes, let's delete it.
+/// book_reviews.remove("The Adventures of Sherlock Holmes");
+///
+/// // look up the values associated with some keys.
+/// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
+/// for book in &to_find {
+///     match book_reviews.get(book) {
+///         Some(review) => println!("{}: {}", book, review),
+///         None => println!("{} is unreviewed.", book)
+///     }
+/// }
+///
+/// // iterate over everything.
+/// for (book, review) in &book_reviews {
+///     println!("{}: \"{}\"", book, review);
+/// }
+/// ```
+///
+/// `HashMap` also implements an [`Entry API`](#method.entry), which allows
+/// for more complex methods of getting, setting, updating and removing keys and
+/// their values:
+///
+/// ```
+/// use std::collections::HashMap;
+///
+/// // type inference lets us omit an explicit type signature (which
+/// // would be `HashMap<&str, u8>` in this example).
+/// let mut player_stats = HashMap::new();
+///
+/// fn random_stat_buff() -> u8 {
+///     // could actually return some random value here - let's just return
+///     // some fixed value for now
+///     42
+/// }
+///
+/// // insert a key only if it doesn't already exist
+/// player_stats.entry("health").or_insert(100);
+///
+/// // insert a key using a function that provides a new value only if it
+/// // doesn't already exist
+/// player_stats.entry("defence").or_insert_with(random_stat_buff);
+///
+/// // update a key, guarding against the key possibly not being set
+/// let stat = player_stats.entry("attack").or_insert(100);
+/// *stat += random_stat_buff();
+/// ```
+///
+/// The easiest way to use `HashMap` with a custom type as key is to derive [`Eq`] and [`Hash`].
+/// We must also derive [`PartialEq`].
+///
+/// [`Eq`]: ../../std/cmp/trait.Eq.html
+/// [`Hash`]: ../../std/hash/trait.Hash.html
+/// [`PartialEq`]: ../../std/cmp/trait.PartialEq.html
+/// [`RefCell`]: ../../std/cell/struct.RefCell.html
+/// [`Cell`]: ../../std/cell/struct.Cell.html
+///
+/// ```
+/// use std::collections::HashMap;
+///
+/// #[derive(Hash, Eq, PartialEq, Debug)]
+/// struct Viking {
+///     name: String,
+///     country: String,
+/// }
+///
+/// impl Viking {
+///     /// Create a new Viking.
+///     fn new(name: &str, country: &str) -> Viking {
+///         Viking { name: name.to_string(), country: country.to_string() }
+///     }
+/// }
+///
+/// // Use a HashMap to store the vikings' health points.
+/// let mut vikings = HashMap::new();
+///
+/// vikings.insert(Viking::new("Einar", "Norway"), 25);
+/// vikings.insert(Viking::new("Olaf", "Denmark"), 24);
+/// vikings.insert(Viking::new("Harald", "Iceland"), 12);
+///
+/// // Use derived implementation to print the status of the vikings.
+/// for (viking, health) in &vikings {
+///     println!("{:?} has {} hp", viking, health);
+/// }
+/// ```
+///
+/// A HashMap with fixed list of elements can be initialized from an array:
+///
+/// ```
+/// use std::collections::HashMap;
+///
+/// fn main() {
+///     let timber_resources: HashMap<&str, i32> =
+///     [("Norway", 100),
+///      ("Denmark", 50),
+///      ("Iceland", 10)]
+///      .iter().cloned().collect();
+///     // use the values stored in map
+/// }
+/// ```
+
+#[derive(Clone)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct HashMap<K, V, S = RandomState> {
+    // All hashes are keyed on these values, to prevent hash collision attacks.
+    hash_builder: S,
+
+    table: RawTable<K, V>,
+
+    resize_policy: DefaultResizePolicy,
+}
+
+/// Search for a pre-hashed key.
+#[inline]
+fn search_hashed<K, V, M, F>(table: M, hash: SafeHash, mut is_match: F) -> InternalEntry<K, V, M>
+    where M: Deref<Target = RawTable<K, V>>,
+          F: FnMut(&K) -> bool
+{
+    // This is the only function where capacity can be zero. To avoid
+    // undefined behavior when Bucket::new gets the raw bucket in this
+    // case, immediately return the appropriate search result.
+    if table.capacity() == 0 {
+        return InternalEntry::TableIsEmpty;
+    }
+
+    let size = table.size();
+    let mut probe = Bucket::new(table, hash);
+    let mut displacement = 0;
+
+    loop {
+        let full = match probe.peek() {
+            Empty(bucket) => {
+                // Found a hole!
+                return InternalEntry::Vacant {
+                    hash: hash,
+                    elem: NoElem(bucket),
+                };
+            }
+            Full(bucket) => bucket,
+        };
+
+        let probe_displacement = full.displacement();
+
+        if probe_displacement < displacement {
+            // Found a luckier bucket than me.
+            // We can finish the search early if we hit any bucket
+            // with a lower distance to initial bucket than we've probed.
+            return InternalEntry::Vacant {
+                hash: hash,
+                elem: NeqElem(full, probe_displacement),
+            };
+        }
+
+        // If the hash doesn't match, it can't be this one..
+        if hash == full.hash() {
+            // If the key doesn't match, it can't be this one..
+            if is_match(full.read().0) {
+                return InternalEntry::Occupied { elem: full };
+            }
+        }
+        displacement += 1;
+        probe = full.next();
+        debug_assert!(displacement <= size);
+    }
+}
+
+fn pop_internal<K, V>(starting_bucket: FullBucketMut<K, V>) -> (K, V) {
+    let (empty, retkey, retval) = starting_bucket.take();
+    let mut gap = match empty.gap_peek() {
+        Some(b) => b,
+        None => return (retkey, retval),
+    };
+
+    while gap.full().displacement() != 0 {
+        gap = match gap.shift() {
+            Some(b) => b,
+            None => break,
+        };
+    }
+
+    // Now we've done all our shifting. Return the value we grabbed earlier.
+    (retkey, retval)
+}
+
+/// Perform robin hood bucket stealing at the given `bucket`. You must
+/// also pass that bucket's displacement so we don't have to recalculate it.
+///
+/// `hash`, `k`, and `v` are the elements to "robin hood" into the hashtable.
+fn robin_hood<'a, K: 'a, V: 'a>(bucket: FullBucketMut<'a, K, V>,
+                                mut displacement: usize,
+                                mut hash: SafeHash,
+                                mut key: K,
+                                mut val: V)
+                                -> &'a mut V {
+    let starting_index = bucket.index();
+    let size = bucket.table().size();
+    // Save the *starting point*.
+    let mut bucket = bucket.stash();
+    // There can be at most `size - dib` buckets to displace, because
+    // in the worst case, there are `size` elements and we already are
+    // `displacement` buckets away from the initial one.
+    let idx_end = starting_index + size - bucket.displacement();
+
+    loop {
+        let (old_hash, old_key, old_val) = bucket.replace(hash, key, val);
+        hash = old_hash;
+        key = old_key;
+        val = old_val;
+
+        loop {
+            displacement += 1;
+            let probe = bucket.next();
+            debug_assert!(probe.index() != idx_end);
+
+            let full_bucket = match probe.peek() {
+                Empty(bucket) => {
+                    // Found a hole!
+                    let bucket = bucket.put(hash, key, val);
+                    // Now that it's stolen, just read the value's pointer
+                    // right out of the table! Go back to the *starting point*.
+                    //
+                    // This use of `into_table` is misleading. It turns the
+                    // bucket, which is a FullBucket on top of a
+                    // FullBucketMut, into just one FullBucketMut. The "table"
+                    // refers to the inner FullBucketMut in this context.
+                    return bucket.into_table().into_mut_refs().1;
+                }
+                Full(bucket) => bucket,
+            };
+
+            let probe_displacement = full_bucket.displacement();
+
+            bucket = full_bucket;
+
+            // Robin hood! Steal the spot.
+            if probe_displacement < displacement {
+                displacement = probe_displacement;
+                break;
+            }
+        }
+    }
+}
+
+impl<K, V, S> HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher
+{
+    fn make_hash<X: ?Sized>(&self, x: &X) -> SafeHash
+        where X: Hash
+    {
+        table::make_hash(&self.hash_builder, x)
+    }
+
+    /// Search for a key, yielding the index if it's found in the hashtable.
+    /// If you already have the hash for the key lying around, use
+    /// search_hashed.
+    #[inline]
+    fn search<'a, Q: ?Sized>(&'a self, q: &Q) -> InternalEntry<K, V, &'a RawTable<K, V>>
+        where K: Borrow<Q>,
+              Q: Eq + Hash
+    {
+        let hash = self.make_hash(q);
+        search_hashed(&self.table, hash, |k| q.eq(k.borrow()))
+    }
+
+    #[inline]
+    fn search_mut<'a, Q: ?Sized>(&'a mut self, q: &Q) -> InternalEntry<K, V, &'a mut RawTable<K, V>>
+        where K: Borrow<Q>,
+              Q: Eq + Hash
+    {
+        let hash = self.make_hash(q);
+        search_hashed(&mut self.table, hash, |k| q.eq(k.borrow()))
+    }
+
+    // The caller should ensure that invariants by Robin Hood Hashing hold
+    // and that there's space in the underlying table.
+    fn insert_hashed_ordered(&mut self, hash: SafeHash, k: K, v: V) {
+        let raw_cap = self.raw_capacity();
+        let mut buckets = Bucket::new(&mut self.table, hash);
+        // note that buckets.index() keeps increasing
+        // even if the pointer wraps back to the first bucket.
+        let limit_bucket = buckets.index() + raw_cap;
+
+        loop {
+            // We don't need to compare hashes for value swap.
+            // Not even DIBs for Robin Hood.
+            buckets = match buckets.peek() {
+                Empty(empty) => {
+                    empty.put(hash, k, v);
+                    return;
+                }
+                Full(b) => b.into_bucket(),
+            };
+            buckets.next();
+            debug_assert!(buckets.index() < limit_bucket);
+        }
+    }
+}
+
+impl<K: Hash + Eq, V> HashMap<K, V, RandomState> {
+    /// Creates an empty `HashMap`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// let mut map: HashMap<&str, isize> = HashMap::new();
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn new() -> HashMap<K, V, RandomState> {
+        Default::default()
+    }
+
+    /// Creates an empty `HashMap` with the specified capacity.
+    ///
+    /// The hash map will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash map will not allocate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// let mut map: HashMap<&str, isize> = HashMap::with_capacity(10);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
+        HashMap::with_capacity_and_hasher(capacity, Default::default())
+    }
+}
+
+impl<K, V, S> HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher
+{
+    /// Creates an empty `HashMap` which will use the given hash builder to hash
+    /// keys.
+    ///
+    /// The created map has the default initial capacity.
+    ///
+    /// Warning: `hash_builder` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::RandomState;
+    ///
+    /// let s = RandomState::new();
+    /// let mut map = HashMap::with_hasher(s);
+    /// map.insert(1, 2);
+    /// ```
+    #[inline]
+    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+    pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
+        HashMap {
+            hash_builder: hash_builder,
+            resize_policy: DefaultResizePolicy::new(),
+            table: RawTable::new(0),
+        }
+    }
+
+    /// Creates an empty `HashMap` with the specified capacity, using `hasher`
+    /// to hash the keys.
+    ///
+    /// The hash map will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash map will not allocate.
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::RandomState;
+    ///
+    /// let s = RandomState::new();
+    /// let mut map = HashMap::with_capacity_and_hasher(10, s);
+    /// map.insert(1, 2);
+    /// ```
+    #[inline]
+    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+    pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> HashMap<K, V, S> {
+        let resize_policy = DefaultResizePolicy::new();
+        let raw_cap = resize_policy.raw_capacity(capacity);
+        HashMap {
+            hash_builder: hash_builder,
+            resize_policy: resize_policy,
+            table: RawTable::new(raw_cap),
+        }
+    }
+
+    /// Returns a reference to the map's hasher.
+    #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
+    pub fn hasher(&self) -> &S {
+        &self.hash_builder
+    }
+
+    /// Returns the number of elements the map can hold without reallocating.
+    ///
+    /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
+    /// more, but is guaranteed to be able to hold at least this many.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// let map: HashMap<isize, isize> = HashMap::with_capacity(100);
+    /// assert!(map.capacity() >= 100);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn capacity(&self) -> usize {
+        self.resize_policy.capacity(self.raw_capacity())
+    }
+
+    /// Returns the hash map's raw capacity.
+    #[inline]
+    fn raw_capacity(&self) -> usize {
+        self.table.capacity()
+    }
+
+    /// Reserves capacity for at least `additional` more elements to be inserted
+    /// in the `HashMap`. The collection may reserve more space to avoid
+    /// frequent reallocations.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new allocation size overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// let mut map: HashMap<&str, isize> = HashMap::new();
+    /// map.reserve(10);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn reserve(&mut self, additional: usize) {
+        let remaining = self.capacity() - self.len(); // this can't overflow
+        if remaining < additional {
+            let min_cap = self.len().checked_add(additional).expect("reserve overflow");
+            let raw_cap = self.resize_policy.raw_capacity(min_cap);
+            self.resize(raw_cap);
+        }
+    }
+
+    /// Resizes the internal vectors to a new capacity. It's your
+    /// responsibility to:
+    ///   1) Ensure `new_raw_cap` is enough for all the elements, accounting
+    ///      for the load factor.
+    ///   2) Ensure `new_raw_cap` is a power of two or zero.
+    fn resize(&mut self, new_raw_cap: usize) {
+        assert!(self.table.size() <= new_raw_cap);
+        assert!(new_raw_cap.is_power_of_two() || new_raw_cap == 0);
+
+        let mut old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
+        let old_size = old_table.size();
+
+        if old_table.capacity() == 0 || old_table.size() == 0 {
+            return;
+        }
+
+        // Grow the table.
+        // Specialization of the other branch.
+        let mut bucket = Bucket::first(&mut old_table);
+
+        // "So a few of the first shall be last: for many be called,
+        // but few chosen."
+        //
+        // We'll most likely encounter a few buckets at the beginning that
+        // have their initial buckets near the end of the table. They were
+        // placed at the beginning as the probe wrapped around the table
+        // during insertion. We must skip forward to a bucket that won't
+        // get reinserted too early and won't unfairly steal others spot.
+        // This eliminates the need for robin hood.
+        loop {
+            bucket = match bucket.peek() {
+                Full(full) => {
+                    if full.displacement() == 0 {
+                        // This bucket occupies its ideal spot.
+                        // It indicates the start of another "cluster".
+                        bucket = full.into_bucket();
+                        break;
+                    }
+                    // Leaving this bucket in the last cluster for later.
+                    full.into_bucket()
+                }
+                Empty(b) => {
+                    // Encountered a hole between clusters.
+                    b.into_bucket()
+                }
+            };
+            bucket.next();
+        }
+
+        // This is how the buckets might be laid out in memory:
+        // ($ marks an initialized bucket)
+        //  ________________
+        // |$$$_$$$$$$_$$$$$|
+        //
+        // But we've skipped the entire initial cluster of buckets
+        // and will continue iteration in this order:
+        //  ________________
+        //     |$$$$$$_$$$$$
+        //                  ^ wrap around once end is reached
+        //  ________________
+        //  $$$_____________|
+        //    ^ exit once table.size == 0
+        loop {
+            bucket = match bucket.peek() {
+                Full(bucket) => {
+                    let h = bucket.hash();
+                    let (b, k, v) = bucket.take();
+                    self.insert_hashed_ordered(h, k, v);
+                    if b.table().size() == 0 {
+                        break;
+                    }
+                    b.into_bucket()
+                }
+                Empty(b) => b.into_bucket(),
+            };
+            bucket.next();
+        }
+
+        assert_eq!(self.table.size(), old_size);
+    }
+
+    /// Shrinks the capacity of the map as much as possible. It will drop
+    /// down as much as possible while maintaining the internal rules
+    /// and possibly leaving some space in accordance with the resize policy.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<isize, isize> = HashMap::with_capacity(100);
+    /// map.insert(1, 2);
+    /// map.insert(3, 4);
+    /// assert!(map.capacity() >= 100);
+    /// map.shrink_to_fit();
+    /// assert!(map.capacity() >= 2);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn shrink_to_fit(&mut self) {
+        let new_raw_cap = self.resize_policy.raw_capacity(self.len());
+        if self.raw_capacity() != new_raw_cap {
+            let old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
+            let old_size = old_table.size();
+
+            // Shrink the table. Naive algorithm for resizing:
+            for (h, k, v) in old_table.into_iter() {
+                self.insert_hashed_nocheck(h, k, v);
+            }
+
+            debug_assert_eq!(self.table.size(), old_size);
+        }
+    }
+
+    /// Insert a pre-hashed key-value pair, without first checking
+    /// that there's enough room in the buckets. Returns a reference to the
+    /// newly insert value.
+    ///
+    /// If the key already exists, the hashtable will be returned untouched
+    /// and a reference to the existing element will be returned.
+    fn insert_hashed_nocheck(&mut self, hash: SafeHash, k: K, v: V) -> Option<V> {
+        let entry = search_hashed(&mut self.table, hash, |key| *key == k).into_entry(k);
+        match entry {
+            Some(Occupied(mut elem)) => Some(elem.insert(v)),
+            Some(Vacant(elem)) => {
+                elem.insert(v);
+                None
+            }
+            None => unreachable!(),
+        }
+    }
+
+    /// An iterator visiting all keys in arbitrary order.
+    /// Iterator element type is `&'a K`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// for key in map.keys() {
+    ///     println!("{}", key);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn keys(&self) -> Keys<K, V> {
+        Keys { inner: self.iter() }
+    }
+
+    /// An iterator visiting all values in arbitrary order.
+    /// Iterator element type is `&'a V`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// for val in map.values() {
+    ///     println!("{}", val);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn values(&self) -> Values<K, V> {
+        Values { inner: self.iter() }
+    }
+
+    /// An iterator visiting all values mutably in arbitrary order.
+    /// Iterator element type is `&'a mut V`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    ///
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// for val in map.values_mut() {
+    ///     *val = *val + 10;
+    /// }
+    ///
+    /// for val in map.values() {
+    ///     println!("{}", val);
+    /// }
+    /// ```
+    #[stable(feature = "map_values_mut", since = "1.10.0")]
+    pub fn values_mut(&mut self) -> ValuesMut<K, V> {
+        ValuesMut { inner: self.iter_mut() }
+    }
+
+    /// An iterator visiting all key-value pairs in arbitrary order.
+    /// Iterator element type is `(&'a K, &'a V)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// for (key, val) in map.iter() {
+    ///     println!("key: {} val: {}", key, val);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn iter(&self) -> Iter<K, V> {
+        Iter { inner: self.table.iter() }
+    }
+
+    /// An iterator visiting all key-value pairs in arbitrary order,
+    /// with mutable references to the values.
+    /// Iterator element type is `(&'a K, &'a mut V)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// // Update all values
+    /// for (_, val) in map.iter_mut() {
+    ///     *val *= 2;
+    /// }
+    ///
+    /// for (key, val) in &map {
+    ///     println!("key: {} val: {}", key, val);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn iter_mut(&mut self) -> IterMut<K, V> {
+        IterMut { inner: self.table.iter_mut() }
+    }
+
+    /// Gets the given key's corresponding entry in the map for in-place manipulation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut letters = HashMap::new();
+    ///
+    /// for ch in "a short treatise on fungi".chars() {
+    ///     let counter = letters.entry(ch).or_insert(0);
+    ///     *counter += 1;
+    /// }
+    ///
+    /// assert_eq!(letters[&'s'], 2);
+    /// assert_eq!(letters[&'t'], 3);
+    /// assert_eq!(letters[&'u'], 1);
+    /// assert_eq!(letters.get(&'y'), None);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn entry(&mut self, key: K) -> Entry<K, V> {
+        // Gotta resize now.
+        self.reserve(1);
+        self.search_mut(&key).into_entry(key).expect("unreachable")
+    }
+
+    /// Returns the number of elements in the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// assert_eq!(a.len(), 0);
+    /// a.insert(1, "a");
+    /// assert_eq!(a.len(), 1);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn len(&self) -> usize {
+        self.table.size()
+    }
+
+    /// Returns true if the map contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// assert!(a.is_empty());
+    /// a.insert(1, "a");
+    /// assert!(!a.is_empty());
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Clears the map, returning all key-value pairs as an iterator. Keeps the
+    /// allocated memory for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// a.insert(1, "a");
+    /// a.insert(2, "b");
+    ///
+    /// for (k, v) in a.drain().take(1) {
+    ///     assert!(k == 1 || k == 2);
+    ///     assert!(v == "a" || v == "b");
+    /// }
+    ///
+    /// assert!(a.is_empty());
+    /// ```
+    #[inline]
+    #[stable(feature = "drain", since = "1.6.0")]
+    pub fn drain(&mut self) -> Drain<K, V> {
+        Drain { inner: self.table.drain() }
+    }
+
+    /// Clears the map, removing all key-value pairs. Keeps the allocated memory
+    /// for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// a.insert(1, "a");
+    /// a.clear();
+    /// assert!(a.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn clear(&mut self) {
+        self.drain();
+    }
+
+    /// Returns a reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: ../../std/cmp/trait.Eq.html
+    /// [`Hash`]: ../../std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// assert_eq!(map.get(&1), Some(&"a"));
+    /// assert_eq!(map.get(&2), None);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
+        where K: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        self.search(k).into_occupied_bucket().map(|bucket| bucket.into_refs().1)
+    }
+
+    /// Returns true if the map contains a value for the specified key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: ../../std/cmp/trait.Eq.html
+    /// [`Hash`]: ../../std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// assert_eq!(map.contains_key(&1), true);
+    /// assert_eq!(map.contains_key(&2), false);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
+        where K: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        self.search(k).into_occupied_bucket().is_some()
+    }
+
+    /// Returns a mutable reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: ../../std/cmp/trait.Eq.html
+    /// [`Hash`]: ../../std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// if let Some(x) = map.get_mut(&1) {
+    ///     *x = "b";
+    /// }
+    /// assert_eq!(map[&1], "b");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
+        where K: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        self.search_mut(k).into_occupied_bucket().map(|bucket| bucket.into_mut_refs().1)
+    }
+
+    /// Inserts a key-value pair into the map.
+    ///
+    /// If the map did not have this key present, `None` is returned.
+    ///
+    /// If the map did have this key present, the value is updated, and the old
+    /// value is returned. The key is not updated, though; this matters for
+    /// types that can be `==` without being identical. See the [module-level
+    /// documentation] for more.
+    ///
+    /// [module-level documentation]: index.html#insert-and-complex-keys
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// assert_eq!(map.insert(37, "a"), None);
+    /// assert_eq!(map.is_empty(), false);
+    ///
+    /// map.insert(37, "b");
+    /// assert_eq!(map.insert(37, "c"), Some("b"));
+    /// assert_eq!(map[&37], "c");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn insert(&mut self, k: K, v: V) -> Option<V> {
+        let hash = self.make_hash(&k);
+        self.reserve(1);
+        self.insert_hashed_nocheck(hash, k, v)
+    }
+
+    /// Removes a key from the map, returning the value at the key if the key
+    /// was previously in the map.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: ../../std/cmp/trait.Eq.html
+    /// [`Hash`]: ../../std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// assert_eq!(map.remove(&1), Some("a"));
+    /// assert_eq!(map.remove(&1), None);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
+        where K: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        if self.table.size() == 0 {
+            return None;
+        }
+
+        self.search_mut(k).into_occupied_bucket().map(|bucket| pop_internal(bucket).1)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V, S> PartialEq for HashMap<K, V, S>
+    where K: Eq + Hash,
+          V: PartialEq,
+          S: BuildHasher
+{
+    fn eq(&self, other: &HashMap<K, V, S>) -> bool {
+        if self.len() != other.len() {
+            return false;
+        }
+
+        self.iter().all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V, S> Eq for HashMap<K, V, S>
+    where K: Eq + Hash,
+          V: Eq,
+          S: BuildHasher
+{
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V, S> Debug for HashMap<K, V, S>
+    where K: Eq + Hash + Debug,
+          V: Debug,
+          S: BuildHasher
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_map().entries(self.iter()).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V, S> Default for HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher + Default
+{
+    /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
+    fn default() -> HashMap<K, V, S> {
+        HashMap::with_hasher(Default::default())
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, Q: ?Sized, V, S> Index<&'a Q> for HashMap<K, V, S>
+    where K: Eq + Hash + Borrow<Q>,
+          Q: Eq + Hash,
+          S: BuildHasher
+{
+    type Output = V;
+
+    #[inline]
+    fn index(&self, index: &Q) -> &V {
+        self.get(index).expect("no entry found for key")
+    }
+}
+
+/// HashMap iterator.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Iter<'a, K: 'a, V: 'a> {
+    inner: table::Iter<'a, K, V>,
+}
+
+// FIXME(#19839) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> Clone for Iter<'a, K, V> {
+    fn clone(&self) -> Iter<'a, K, V> {
+        Iter { inner: self.inner.clone() }
+    }
+}
+
+/// HashMap mutable values iterator.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct IterMut<'a, K: 'a, V: 'a> {
+    inner: table::IterMut<'a, K, V>,
+}
+
+/// HashMap move iterator.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct IntoIter<K, V> {
+    inner: table::IntoIter<K, V>,
+}
+
+/// HashMap keys iterator.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Keys<'a, K: 'a, V: 'a> {
+    inner: Iter<'a, K, V>,
+}
+
+// FIXME(#19839) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> Clone for Keys<'a, K, V> {
+    fn clone(&self) -> Keys<'a, K, V> {
+        Keys { inner: self.inner.clone() }
+    }
+}
+
+/// HashMap values iterator.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Values<'a, K: 'a, V: 'a> {
+    inner: Iter<'a, K, V>,
+}
+
+// FIXME(#19839) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> Clone for Values<'a, K, V> {
+    fn clone(&self) -> Values<'a, K, V> {
+        Values { inner: self.inner.clone() }
+    }
+}
+
+/// HashMap drain iterator.
+#[stable(feature = "drain", since = "1.6.0")]
+pub struct Drain<'a, K: 'a, V: 'a> {
+    inner: table::Drain<'a, K, V>,
+}
+
+/// Mutable HashMap values iterator.
+#[stable(feature = "map_values_mut", since = "1.10.0")]
+pub struct ValuesMut<'a, K: 'a, V: 'a> {
+    inner: IterMut<'a, K, V>,
+}
+
+enum InternalEntry<K, V, M> {
+    Occupied { elem: FullBucket<K, V, M> },
+    Vacant {
+        hash: SafeHash,
+        elem: VacantEntryState<K, V, M>,
+    },
+    TableIsEmpty,
+}
+
+impl<K, V, M> InternalEntry<K, V, M> {
+    #[inline]
+    fn into_occupied_bucket(self) -> Option<FullBucket<K, V, M>> {
+        match self {
+            InternalEntry::Occupied { elem } => Some(elem),
+            _ => None,
+        }
+    }
+}
+
+impl<'a, K, V> InternalEntry<K, V, &'a mut RawTable<K, V>> {
+    #[inline]
+    fn into_entry(self, key: K) -> Option<Entry<'a, K, V>> {
+        match self {
+            InternalEntry::Occupied { elem } => {
+                Some(Occupied(OccupiedEntry {
+                    key: Some(key),
+                    elem: elem,
+                }))
+            }
+            InternalEntry::Vacant { hash, elem } => {
+                Some(Vacant(VacantEntry {
+                    hash: hash,
+                    key: key,
+                    elem: elem,
+                }))
+            }
+            InternalEntry::TableIsEmpty => None,
+        }
+    }
+}
+
+/// A view into a single location in a map, which may be vacant or occupied.
+/// This enum is constructed from the [`entry`] method on [`HashMap`].
+///
+/// [`HashMap`]: struct.HashMap.html
+/// [`entry`]: struct.HashMap.html#method.entry
+#[stable(feature = "rust1", since = "1.0.0")]
+pub enum Entry<'a, K: 'a, V: 'a> {
+    /// An occupied Entry.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Occupied(#[stable(feature = "rust1", since = "1.0.0")]
+             OccupiedEntry<'a, K, V>),
+
+    /// A vacant Entry.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Vacant(#[stable(feature = "rust1", since = "1.0.0")]
+           VacantEntry<'a, K, V>),
+}
+
+#[stable(feature= "debug_hash_map", since = "1.12.0")]
+impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for Entry<'a, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Vacant(ref v) => {
+                f.debug_tuple("Entry")
+                    .field(v)
+                    .finish()
+            }
+            Occupied(ref o) => {
+                f.debug_tuple("Entry")
+                    .field(o)
+                    .finish()
+            }
+        }
+    }
+}
+
+/// A view into a single occupied location in a HashMap.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
+    key: Option<K>,
+    elem: FullBucket<K, V, &'a mut RawTable<K, V>>,
+}
+
+#[stable(feature= "debug_hash_map", since = "1.12.0")]
+impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for OccupiedEntry<'a, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("OccupiedEntry")
+            .field("key", self.key())
+            .field("value", self.get())
+            .finish()
+    }
+}
+
+/// A view into a single empty location in a HashMap.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct VacantEntry<'a, K: 'a, V: 'a> {
+    hash: SafeHash,
+    key: K,
+    elem: VacantEntryState<K, V, &'a mut RawTable<K, V>>,
+}
+
+#[stable(feature= "debug_hash_map", since = "1.12.0")]
+impl<'a, K: 'a + Debug, V: 'a> Debug for VacantEntry<'a, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("VacantEntry")
+            .field(self.key())
+            .finish()
+    }
+}
+
+/// Possible states of a VacantEntry.
+enum VacantEntryState<K, V, M> {
+    /// The index is occupied, but the key to insert has precedence,
+    /// and will kick the current one out on insertion.
+    NeqElem(FullBucket<K, V, M>, usize),
+    /// The index is genuinely vacant.
+    NoElem(EmptyBucket<K, V, M>),
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = (&'a K, &'a V);
+    type IntoIter = Iter<'a, K, V>;
+
+    fn into_iter(self) -> Iter<'a, K, V> {
+        self.iter()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = (&'a K, &'a mut V);
+    type IntoIter = IterMut<'a, K, V>;
+
+    fn into_iter(mut self) -> IterMut<'a, K, V> {
+        self.iter_mut()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V, S> IntoIterator for HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = (K, V);
+    type IntoIter = IntoIter<K, V>;
+
+    /// Creates a consuming iterator, that is, one that moves each key-value
+    /// pair out of the map in arbitrary order. The map cannot be used after
+    /// calling this.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// // Not possible with .iter()
+    /// let vec: Vec<(&str, isize)> = map.into_iter().collect();
+    /// ```
+    fn into_iter(self) -> IntoIter<K, V> {
+        IntoIter { inner: self.table.into_iter() }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> Iterator for Iter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(&'a K, &'a V)> {
+        self.inner.next()
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Iter<'a, K, V> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
+        self.inner.next()
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V> Iterator for IntoIter<K, V> {
+    type Item = (K, V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(K, V)> {
+        self.inner.next().map(|(_, k, v)| (k, v))
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V> ExactSizeIterator for IntoIter<K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<K, V> FusedIterator for IntoIter<K, V> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> Iterator for Keys<'a, K, V> {
+    type Item = &'a K;
+
+    #[inline]
+    fn next(&mut self) -> Option<(&'a K)> {
+        self.inner.next().map(|(k, _)| k)
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Keys<'a, K, V> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> Iterator for Values<'a, K, V> {
+    type Item = &'a V;
+
+    #[inline]
+    fn next(&mut self) -> Option<(&'a V)> {
+        self.inner.next().map(|(_, v)| v)
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Values<'a, K, V> {}
+
+#[stable(feature = "map_values_mut", since = "1.10.0")]
+impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
+    type Item = &'a mut V;
+
+    #[inline]
+    fn next(&mut self) -> Option<(&'a mut V)> {
+        self.inner.next().map(|(_, v)| v)
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+#[stable(feature = "map_values_mut", since = "1.10.0")]
+impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for ValuesMut<'a, K, V> {}
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, K, V> Iterator for Drain<'a, K, V> {
+    type Item = (K, V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(K, V)> {
+        self.inner.next().map(|(_, k, v)| (k, v))
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Drain<'a, K, V> {}
+
+impl<'a, K, V> Entry<'a, K, V> {
+    #[stable(feature = "rust1", since = "1.0.0")]
+    /// Ensures a value is in the entry by inserting the default if empty, and returns
+    /// a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// assert_eq!(map["poneyland"], 12);
+    ///
+    /// *map.entry("poneyland").or_insert(12) += 10;
+    /// assert_eq!(map["poneyland"], 22);
+    /// ```
+    pub fn or_insert(self, default: V) -> &'a mut V {
+        match self {
+            Occupied(entry) => entry.into_mut(),
+            Vacant(entry) => entry.insert(default),
+        }
+    }
+
+    #[stable(feature = "rust1", since = "1.0.0")]
+    /// Ensures a value is in the entry by inserting the result of the default function if empty,
+    /// and returns a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<&str, String> = HashMap::new();
+    /// let s = "hoho".to_owned();
+    ///
+    /// map.entry("poneyland").or_insert_with(|| s);
+    ///
+    /// assert_eq!(map["poneyland"], "hoho".to_owned());
+    /// ```
+    pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
+        match self {
+            Occupied(entry) => entry.into_mut(),
+            Vacant(entry) => entry.insert(default()),
+        }
+    }
+
+    /// Returns a reference to this entry's key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
+    /// ```
+    #[stable(feature = "map_entry_keys", since = "1.10.0")]
+    pub fn key(&self) -> &K {
+        match *self {
+            Occupied(ref entry) => entry.key(),
+            Vacant(ref entry) => entry.key(),
+        }
+    }
+}
+
+impl<'a, K, V> OccupiedEntry<'a, K, V> {
+    /// Gets a reference to the key in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
+    /// ```
+    #[stable(feature = "map_entry_keys", since = "1.10.0")]
+    pub fn key(&self) -> &K {
+        self.elem.read().0
+    }
+
+    /// Deprecated, renamed to `remove_entry`
+    #[unstable(feature = "map_entry_recover_keys", issue = "34285")]
+    #[rustc_deprecated(since = "1.12.0", reason = "renamed to `remove_entry`")]
+    pub fn remove_pair(self) -> (K, V) {
+        self.remove_entry()
+    }
+
+    /// Take the ownership of the key and value from the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// if let Entry::Occupied(o) = map.entry("poneyland") {
+    ///     // We delete the entry from the map.
+    ///     o.remove_entry();
+    /// }
+    ///
+    /// assert_eq!(map.contains_key("poneyland"), false);
+    /// ```
+    #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
+    pub fn remove_entry(self) -> (K, V) {
+        pop_internal(self.elem)
+    }
+
+    /// Gets a reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// if let Entry::Occupied(o) = map.entry("poneyland") {
+    ///     assert_eq!(o.get(), &12);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn get(&self) -> &V {
+        self.elem.read().1
+    }
+
+    /// Gets a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// assert_eq!(map["poneyland"], 12);
+    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
+    ///      *o.get_mut() += 10;
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 22);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn get_mut(&mut self) -> &mut V {
+        self.elem.read_mut().1
+    }
+
+    /// Converts the OccupiedEntry into a mutable reference to the value in the entry
+    /// with a lifetime bound to the map itself.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// assert_eq!(map["poneyland"], 12);
+    /// if let Entry::Occupied(o) = map.entry("poneyland") {
+    ///     *o.into_mut() += 10;
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 22);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn into_mut(self) -> &'a mut V {
+        self.elem.into_mut_refs().1
+    }
+
+    /// Sets the value of the entry, and returns the entry's old value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
+    ///     assert_eq!(o.insert(15), 12);
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 15);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn insert(&mut self, mut value: V) -> V {
+        let old_value = self.get_mut();
+        mem::swap(&mut value, old_value);
+        value
+    }
+
+    /// Takes the value out of the entry, and returns it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// if let Entry::Occupied(o) = map.entry("poneyland") {
+    ///     assert_eq!(o.remove(), 12);
+    /// }
+    ///
+    /// assert_eq!(map.contains_key("poneyland"), false);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn remove(self) -> V {
+        pop_internal(self.elem).1
+    }
+
+    /// Returns a key that was used for search.
+    ///
+    /// The key was retained for further use.
+    fn take_key(&mut self) -> Option<K> {
+        self.key.take()
+    }
+}
+
+impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
+    /// Gets a reference to the key that would be used when inserting a value
+    /// through the `VacantEntry`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
+    /// ```
+    #[stable(feature = "map_entry_keys", since = "1.10.0")]
+    pub fn key(&self) -> &K {
+        &self.key
+    }
+
+    /// Take ownership of the key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// if let Entry::Vacant(v) = map.entry("poneyland") {
+    ///     v.into_key();
+    /// }
+    /// ```
+    #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
+    pub fn into_key(self) -> K {
+        self.key
+    }
+
+    /// Sets the value of the entry with the VacantEntry's key,
+    /// and returns a mutable reference to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use std::collections::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// if let Entry::Vacant(o) = map.entry("poneyland") {
+    ///     o.insert(37);
+    /// }
+    /// assert_eq!(map["poneyland"], 37);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn insert(self, value: V) -> &'a mut V {
+        match self.elem {
+            NeqElem(bucket, disp) => robin_hood(bucket, disp, self.hash, self.key, value),
+            NoElem(bucket) => bucket.put(self.hash, self.key, value).into_mut_refs().1,
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher + Default
+{
+    fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> HashMap<K, V, S> {
+        let mut map = HashMap::with_hasher(Default::default());
+        map.extend(iter);
+        map
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
+    where K: Eq + Hash,
+          S: BuildHasher
+{
+    fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
+        // Keys may be already present or show multiple times in the iterator.
+        // Reserve the entire hint lower bound if the map is empty.
+        // Otherwise reserve half the hint (rounded up), so the map
+        // will only resize twice in the worst case.
+        let iter = iter.into_iter();
+        let reserve = if self.is_empty() {
+            iter.size_hint().0
+        } else {
+            (iter.size_hint().0 + 1) / 2
+        };
+        self.reserve(reserve);
+        for (k, v) in iter {
+            self.insert(k, v);
+        }
+    }
+}
+
+#[stable(feature = "hash_extend_copy", since = "1.4.0")]
+impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
+    where K: Eq + Hash + Copy,
+          V: Copy,
+          S: BuildHasher
+{
+    fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
+        self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
+    }
+}
+
+/// `RandomState` is the default state for [`HashMap`] types.
+///
+/// A particular instance `RandomState` will create the same instances of
+/// [`Hasher`], but the hashers created by two different `RandomState`
+/// instances are unlikely to produce the same result for the same values.
+///
+/// [`HashMap`]: struct.HashMap.html
+/// [`Hasher`]: ../../hash/trait.Hasher.html
+///
+/// # Examples
+///
+/// ```
+/// use std::collections::HashMap;
+/// use std::collections::hash_map::RandomState;
+///
+/// let s = RandomState::new();
+/// let mut map = HashMap::with_hasher(s);
+/// map.insert(1, 2);
+/// ```
+#[derive(Clone)]
+#[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+pub struct RandomState {
+    k0: u64,
+    k1: u64,
+}
+
+impl RandomState {
+    /// Constructs a new `RandomState` that is initialized with random keys.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::hash_map::RandomState;
+    ///
+    /// let s = RandomState::new();
+    /// ```
+    #[inline]
+    #[allow(deprecated)]
+    // rand
+    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+    pub fn new() -> RandomState {
+        // Historically this function did not cache keys from the OS and instead
+        // simply always called `rand::thread_rng().gen()` twice. In #31356 it
+        // was discovered, however, that because we re-seed the thread-local RNG
+        // from the OS periodically that this can cause excessive slowdown when
+        // many hash maps are created on a thread. To solve this performance
+        // trap we cache the first set of randomly generated keys per-thread.
+        //
+        // Later in #36481 it was discovered that exposing a deterministic
+        // iteration order allows a form of DOS attack. To counter that we
+        // increment one of the seeds on every RandomState creation, giving
+        // every corresponding HashMap a different iteration order.
+        thread_local!(static KEYS: Cell<(u64, u64)> = {
+            let r = rand::OsRng::new();
+            let mut r = r.expect("failed to create an OS RNG");
+            Cell::new((r.gen(), r.gen()))
+        });
+
+        KEYS.with(|keys| {
+            let (k0, k1) = keys.get();
+            keys.set((k0.wrapping_add(1), k1));
+            RandomState { k0: k0, k1: k1 }
+        })
+    }
+}
+
+#[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+impl BuildHasher for RandomState {
+    type Hasher = DefaultHasher;
+    #[inline]
+    #[allow(deprecated)]
+    fn build_hasher(&self) -> DefaultHasher {
+        DefaultHasher(SipHasher13::new_with_keys(self.k0, self.k1))
+    }
+}
+
+/// The default [`Hasher`] used by [`RandomState`].
+///
+/// The internal algorithm is not specified, and so it and its hashes should
+/// not be relied upon over releases.
+///
+/// [`RandomState`]: struct.RandomState.html
+/// [`Hasher`]: ../../hash/trait.Hasher.html
+#[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
+#[allow(deprecated)]
+#[derive(Debug)]
+pub struct DefaultHasher(SipHasher13);
+
+impl DefaultHasher {
+    /// Creates a new `DefaultHasher`.
+    ///
+    /// This hasher is not guaranteed to be the same as all other
+    /// `DefaultHasher` instances, but is the same as all other `DefaultHasher`
+    /// instances created through `new` or `default`.
+    #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
+    #[allow(deprecated)]
+    pub fn new() -> DefaultHasher {
+        DefaultHasher(SipHasher13::new_with_keys(0, 0))
+    }
+}
+
+#[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
+impl Default for DefaultHasher {
+    /// Creates a new `DefaultHasher` using [`DefaultHasher::new`]. See
+    /// [`DefaultHasher::new`] documentation for more information.
+    ///
+    /// [`DefaultHasher::new`]: #method.new
+    fn default() -> DefaultHasher {
+        DefaultHasher::new()
+    }
+}
+
+#[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
+impl Hasher for DefaultHasher {
+    #[inline]
+    fn write(&mut self, msg: &[u8]) {
+        self.0.write(msg)
+    }
+
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.0.finish()
+    }
+}
+
+#[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+impl Default for RandomState {
+    /// Constructs a new `RandomState`.
+    #[inline]
+    fn default() -> RandomState {
+        RandomState::new()
+    }
+}
+
+impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
+    where K: Eq + Hash + Borrow<Q>,
+          S: BuildHasher,
+          Q: Eq + Hash
+{
+    type Key = K;
+
+    fn get(&self, key: &Q) -> Option<&K> {
+        self.search(key).into_occupied_bucket().map(|bucket| bucket.into_refs().0)
+    }
+
+    fn take(&mut self, key: &Q) -> Option<K> {
+        if self.table.size() == 0 {
+            return None;
+        }
+
+        self.search_mut(key).into_occupied_bucket().map(|bucket| pop_internal(bucket).0)
+    }
+
+    fn replace(&mut self, key: K) -> Option<K> {
+        self.reserve(1);
+
+        match self.entry(key) {
+            Occupied(mut occupied) => {
+                let key = occupied.take_key().unwrap();
+                Some(mem::replace(occupied.elem.read_mut().0, key))
+            }
+            Vacant(vacant) => {
+                vacant.insert(());
+                None
+            }
+        }
+    }
+}
+
+#[allow(dead_code)]
+fn assert_covariance() {
+    fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
+        v
+    }
+    fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
+        v
+    }
+    fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
+        v
+    }
+    fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
+        v
+    }
+    fn into_iter_key<'new>(v: IntoIter<&'static str, u8>) -> IntoIter<&'new str, u8> {
+        v
+    }
+    fn into_iter_val<'new>(v: IntoIter<u8, &'static str>) -> IntoIter<u8, &'new str> {
+        v
+    }
+    fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
+        v
+    }
+    fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
+        v
+    }
+    fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
+        v
+    }
+    fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
+        v
+    }
+    fn drain<'new>(d: Drain<'static, &'static str, &'static str>)
+                   -> Drain<'new, &'new str, &'new str> {
+        d
+    }
+}
+
+#[cfg(test)]
+mod test_map {
+    use super::HashMap;
+    use super::Entry::{Occupied, Vacant};
+    use super::RandomState;
+    use cell::RefCell;
+    use rand::{thread_rng, Rng};
+
+    #[test]
+    fn test_zero_capacities() {
+        type HM = HashMap<i32, i32>;
+
+        let m = HM::new();
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::default();
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::with_hasher(RandomState::new());
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::with_capacity(0);
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::with_capacity_and_hasher(0, RandomState::new());
+        assert_eq!(m.capacity(), 0);
+
+        let mut m = HM::new();
+        m.insert(1, 1);
+        m.insert(2, 2);
+        m.remove(&1);
+        m.remove(&2);
+        m.shrink_to_fit();
+        assert_eq!(m.capacity(), 0);
+
+        let mut m = HM::new();
+        m.reserve(0);
+        assert_eq!(m.capacity(), 0);
+    }
+
+    #[test]
+    fn test_create_capacity_zero() {
+        let mut m = HashMap::with_capacity(0);
+
+        assert!(m.insert(1, 1).is_none());
+
+        assert!(m.contains_key(&1));
+        assert!(!m.contains_key(&0));
+    }
+
+    #[test]
+    fn test_insert() {
+        let mut m = HashMap::new();
+        assert_eq!(m.len(), 0);
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(m.len(), 1);
+        assert!(m.insert(2, 4).is_none());
+        assert_eq!(m.len(), 2);
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert_eq!(*m.get(&2).unwrap(), 4);
+    }
+
+    #[test]
+    fn test_clone() {
+        let mut m = HashMap::new();
+        assert_eq!(m.len(), 0);
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(m.len(), 1);
+        assert!(m.insert(2, 4).is_none());
+        assert_eq!(m.len(), 2);
+        let m2 = m.clone();
+        assert_eq!(*m2.get(&1).unwrap(), 2);
+        assert_eq!(*m2.get(&2).unwrap(), 4);
+        assert_eq!(m2.len(), 2);
+    }
+
+    thread_local! { static DROP_VECTOR: RefCell<Vec<isize>> = RefCell::new(Vec::new()) }
+
+    #[derive(Hash, PartialEq, Eq)]
+    struct Dropable {
+        k: usize,
+    }
+
+    impl Dropable {
+        fn new(k: usize) -> Dropable {
+            DROP_VECTOR.with(|slot| {
+                slot.borrow_mut()[k] += 1;
+            });
+
+            Dropable { k: k }
+        }
+    }
+
+    impl Drop for Dropable {
+        fn drop(&mut self) {
+            DROP_VECTOR.with(|slot| {
+                slot.borrow_mut()[self.k] -= 1;
+            });
+        }
+    }
+
+    impl Clone for Dropable {
+        fn clone(&self) -> Dropable {
+            Dropable::new(self.k)
+        }
+    }
+
+    #[test]
+    fn test_drops() {
+        DROP_VECTOR.with(|slot| {
+            *slot.borrow_mut() = vec![0; 200];
+        });
+
+        {
+            let mut m = HashMap::new();
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 0);
+                }
+            });
+
+            for i in 0..100 {
+                let d1 = Dropable::new(i);
+                let d2 = Dropable::new(i + 100);
+                m.insert(d1, d2);
+            }
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 1);
+                }
+            });
+
+            for i in 0..50 {
+                let k = Dropable::new(i);
+                let v = m.remove(&k);
+
+                assert!(v.is_some());
+
+                DROP_VECTOR.with(|v| {
+                    assert_eq!(v.borrow()[i], 1);
+                    assert_eq!(v.borrow()[i+100], 1);
+                });
+            }
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..50 {
+                    assert_eq!(v.borrow()[i], 0);
+                    assert_eq!(v.borrow()[i+100], 0);
+                }
+
+                for i in 50..100 {
+                    assert_eq!(v.borrow()[i], 1);
+                    assert_eq!(v.borrow()[i+100], 1);
+                }
+            });
+        }
+
+        DROP_VECTOR.with(|v| {
+            for i in 0..200 {
+                assert_eq!(v.borrow()[i], 0);
+            }
+        });
+    }
+
+    #[test]
+    fn test_into_iter_drops() {
+        DROP_VECTOR.with(|v| {
+            *v.borrow_mut() = vec![0; 200];
+        });
+
+        let hm = {
+            let mut hm = HashMap::new();
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 0);
+                }
+            });
+
+            for i in 0..100 {
+                let d1 = Dropable::new(i);
+                let d2 = Dropable::new(i + 100);
+                hm.insert(d1, d2);
+            }
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 1);
+                }
+            });
+
+            hm
+        };
+
+        // By the way, ensure that cloning doesn't screw up the dropping.
+        drop(hm.clone());
+
+        {
+            let mut half = hm.into_iter().take(50);
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 1);
+                }
+            });
+
+            for _ in half.by_ref() {}
+
+            DROP_VECTOR.with(|v| {
+                let nk = (0..100)
+                    .filter(|&i| v.borrow()[i] == 1)
+                    .count();
+
+                let nv = (0..100)
+                    .filter(|&i| v.borrow()[i + 100] == 1)
+                    .count();
+
+                assert_eq!(nk, 50);
+                assert_eq!(nv, 50);
+            });
+        };
+
+        DROP_VECTOR.with(|v| {
+            for i in 0..200 {
+                assert_eq!(v.borrow()[i], 0);
+            }
+        });
+    }
+
+    #[test]
+    fn test_empty_remove() {
+        let mut m: HashMap<isize, bool> = HashMap::new();
+        assert_eq!(m.remove(&0), None);
+    }
+
+    #[test]
+    fn test_empty_entry() {
+        let mut m: HashMap<isize, bool> = HashMap::new();
+        match m.entry(0) {
+            Occupied(_) => panic!(),
+            Vacant(_) => {}
+        }
+        assert!(*m.entry(0).or_insert(true));
+        assert_eq!(m.len(), 1);
+    }
+
+    #[test]
+    fn test_empty_iter() {
+        let mut m: HashMap<isize, bool> = HashMap::new();
+        assert_eq!(m.drain().next(), None);
+        assert_eq!(m.keys().next(), None);
+        assert_eq!(m.values().next(), None);
+        assert_eq!(m.values_mut().next(), None);
+        assert_eq!(m.iter().next(), None);
+        assert_eq!(m.iter_mut().next(), None);
+        assert_eq!(m.len(), 0);
+        assert!(m.is_empty());
+        assert_eq!(m.into_iter().next(), None);
+    }
+
+    #[test]
+    fn test_lots_of_insertions() {
+        let mut m = HashMap::new();
+
+        // Try this a few times to make sure we never screw up the hashmap's
+        // internal state.
+        for _ in 0..10 {
+            assert!(m.is_empty());
+
+            for i in 1..1001 {
+                assert!(m.insert(i, i).is_none());
+
+                for j in 1..i + 1 {
+                    let r = m.get(&j);
+                    assert_eq!(r, Some(&j));
+                }
+
+                for j in i + 1..1001 {
+                    let r = m.get(&j);
+                    assert_eq!(r, None);
+                }
+            }
+
+            for i in 1001..2001 {
+                assert!(!m.contains_key(&i));
+            }
+
+            // remove forwards
+            for i in 1..1001 {
+                assert!(m.remove(&i).is_some());
+
+                for j in 1..i + 1 {
+                    assert!(!m.contains_key(&j));
+                }
+
+                for j in i + 1..1001 {
+                    assert!(m.contains_key(&j));
+                }
+            }
+
+            for i in 1..1001 {
+                assert!(!m.contains_key(&i));
+            }
+
+            for i in 1..1001 {
+                assert!(m.insert(i, i).is_none());
+            }
+
+            // remove backwards
+            for i in (1..1001).rev() {
+                assert!(m.remove(&i).is_some());
+
+                for j in i..1001 {
+                    assert!(!m.contains_key(&j));
+                }
+
+                for j in 1..i {
+                    assert!(m.contains_key(&j));
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_find_mut() {
+        let mut m = HashMap::new();
+        assert!(m.insert(1, 12).is_none());
+        assert!(m.insert(2, 8).is_none());
+        assert!(m.insert(5, 14).is_none());
+        let new = 100;
+        match m.get_mut(&5) {
+            None => panic!(),
+            Some(x) => *x = new,
+        }
+        assert_eq!(m.get(&5), Some(&new));
+    }
+
+    #[test]
+    fn test_insert_overwrite() {
+        let mut m = HashMap::new();
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert!(!m.insert(1, 3).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 3);
+    }
+
+    #[test]
+    fn test_insert_conflicts() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2).is_none());
+        assert!(m.insert(5, 3).is_none());
+        assert!(m.insert(9, 4).is_none());
+        assert_eq!(*m.get(&9).unwrap(), 4);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+        assert_eq!(*m.get(&1).unwrap(), 2);
+    }
+
+    #[test]
+    fn test_conflict_remove() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert!(m.insert(5, 3).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+        assert!(m.insert(9, 4).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+        assert_eq!(*m.get(&9).unwrap(), 4);
+        assert!(m.remove(&1).is_some());
+        assert_eq!(*m.get(&9).unwrap(), 4);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+    }
+
+    #[test]
+    fn test_is_empty() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2).is_none());
+        assert!(!m.is_empty());
+        assert!(m.remove(&1).is_some());
+        assert!(m.is_empty());
+    }
+
+    #[test]
+    fn test_pop() {
+        let mut m = HashMap::new();
+        m.insert(1, 2);
+        assert_eq!(m.remove(&1), Some(2));
+        assert_eq!(m.remove(&1), None);
+    }
+
+    #[test]
+    fn test_iterate() {
+        let mut m = HashMap::with_capacity(4);
+        for i in 0..32 {
+            assert!(m.insert(i, i*2).is_none());
+        }
+        assert_eq!(m.len(), 32);
+
+        let mut observed: u32 = 0;
+
+        for (k, v) in &m {
+            assert_eq!(*v, *k * 2);
+            observed |= 1 << *k;
+        }
+        assert_eq!(observed, 0xFFFF_FFFF);
+    }
+
+    #[test]
+    fn test_keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: HashMap<_, _> = vec.into_iter().collect();
+        let keys: Vec<_> = map.keys().cloned().collect();
+        assert_eq!(keys.len(), 3);
+        assert!(keys.contains(&1));
+        assert!(keys.contains(&2));
+        assert!(keys.contains(&3));
+    }
+
+    #[test]
+    fn test_values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: HashMap<_, _> = vec.into_iter().collect();
+        let values: Vec<_> = map.values().cloned().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&'a'));
+        assert!(values.contains(&'b'));
+        assert!(values.contains(&'c'));
+    }
+
+    #[test]
+    fn test_values_mut() {
+        let vec = vec![(1, 1), (2, 2), (3, 3)];
+        let mut map: HashMap<_, _> = vec.into_iter().collect();
+        for value in map.values_mut() {
+            *value = (*value) * 2
+        }
+        let values: Vec<_> = map.values().cloned().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&2));
+        assert!(values.contains(&4));
+        assert!(values.contains(&6));
+    }
+
+    #[test]
+    fn test_find() {
+        let mut m = HashMap::new();
+        assert!(m.get(&1).is_none());
+        m.insert(1, 2);
+        match m.get(&1) {
+            None => panic!(),
+            Some(v) => assert_eq!(*v, 2),
+        }
+    }
+
+    #[test]
+    fn test_eq() {
+        let mut m1 = HashMap::new();
+        m1.insert(1, 2);
+        m1.insert(2, 3);
+        m1.insert(3, 4);
+
+        let mut m2 = HashMap::new();
+        m2.insert(1, 2);
+        m2.insert(2, 3);
+
+        assert!(m1 != m2);
+
+        m2.insert(3, 4);
+
+        assert_eq!(m1, m2);
+    }
+
+    #[test]
+    fn test_show() {
+        let mut map = HashMap::new();
+        let empty: HashMap<i32, i32> = HashMap::new();
+
+        map.insert(1, 2);
+        map.insert(3, 4);
+
+        let map_str = format!("{:?}", map);
+
+        assert!(map_str == "{1: 2, 3: 4}" ||
+                map_str == "{3: 4, 1: 2}");
+        assert_eq!(format!("{:?}", empty), "{}");
+    }
+
+    #[test]
+    fn test_expand() {
+        let mut m = HashMap::new();
+
+        assert_eq!(m.len(), 0);
+        assert!(m.is_empty());
+
+        let mut i = 0;
+        let old_raw_cap = m.raw_capacity();
+        while old_raw_cap == m.raw_capacity() {
+            m.insert(i, i);
+            i += 1;
+        }
+
+        assert_eq!(m.len(), i);
+        assert!(!m.is_empty());
+    }
+
+    #[test]
+    fn test_behavior_resize_policy() {
+        let mut m = HashMap::new();
+
+        assert_eq!(m.len(), 0);
+        assert_eq!(m.raw_capacity(), 0);
+        assert!(m.is_empty());
+
+        m.insert(0, 0);
+        m.remove(&0);
+        assert!(m.is_empty());
+        let initial_raw_cap = m.raw_capacity();
+        m.reserve(initial_raw_cap);
+        let raw_cap = m.raw_capacity();
+
+        assert_eq!(raw_cap, initial_raw_cap * 2);
+
+        let mut i = 0;
+        for _ in 0..raw_cap * 3 / 4 {
+            m.insert(i, i);
+            i += 1;
+        }
+        // three quarters full
+
+        assert_eq!(m.len(), i);
+        assert_eq!(m.raw_capacity(), raw_cap);
+
+        for _ in 0..raw_cap / 4 {
+            m.insert(i, i);
+            i += 1;
+        }
+        // half full
+
+        let new_raw_cap = m.raw_capacity();
+        assert_eq!(new_raw_cap, raw_cap * 2);
+
+        for _ in 0..raw_cap / 2 - 1 {
+            i -= 1;
+            m.remove(&i);
+            assert_eq!(m.raw_capacity(), new_raw_cap);
+        }
+        // A little more than one quarter full.
+        m.shrink_to_fit();
+        assert_eq!(m.raw_capacity(), raw_cap);
+        // again, a little more than half full
+        for _ in 0..raw_cap / 2 - 1 {
+            i -= 1;
+            m.remove(&i);
+        }
+        m.shrink_to_fit();
+
+        assert_eq!(m.len(), i);
+        assert!(!m.is_empty());
+        assert_eq!(m.raw_capacity(), initial_raw_cap);
+    }
+
+    #[test]
+    fn test_reserve_shrink_to_fit() {
+        let mut m = HashMap::new();
+        m.insert(0, 0);
+        m.remove(&0);
+        assert!(m.capacity() >= m.len());
+        for i in 0..128 {
+            m.insert(i, i);
+        }
+        m.reserve(256);
+
+        let usable_cap = m.capacity();
+        for i in 128..(128 + 256) {
+            m.insert(i, i);
+            assert_eq!(m.capacity(), usable_cap);
+        }
+
+        for i in 100..(128 + 256) {
+            assert_eq!(m.remove(&i), Some(i));
+        }
+        m.shrink_to_fit();
+
+        assert_eq!(m.len(), 100);
+        assert!(!m.is_empty());
+        assert!(m.capacity() >= m.len());
+
+        for i in 0..100 {
+            assert_eq!(m.remove(&i), Some(i));
+        }
+        m.shrink_to_fit();
+        m.insert(0, 0);
+
+        assert_eq!(m.len(), 1);
+        assert!(m.capacity() >= m.len());
+        assert_eq!(m.remove(&0), Some(0));
+    }
+
+    #[test]
+    fn test_from_iter() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<_, _> = xs.iter().cloned().collect();
+
+        for &(k, v) in &xs {
+            assert_eq!(map.get(&k), Some(&v));
+        }
+    }
+
+    #[test]
+    fn test_size_hint() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<_, _> = xs.iter().cloned().collect();
+
+        let mut iter = map.iter();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.size_hint(), (3, Some(3)));
+    }
+
+    #[test]
+    fn test_iter_len() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<_, _> = xs.iter().cloned().collect();
+
+        let mut iter = map.iter();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.len(), 3);
+    }
+
+    #[test]
+    fn test_mut_size_hint() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let mut map: HashMap<_, _> = xs.iter().cloned().collect();
+
+        let mut iter = map.iter_mut();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.size_hint(), (3, Some(3)));
+    }
+
+    #[test]
+    fn test_iter_mut_len() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let mut map: HashMap<_, _> = xs.iter().cloned().collect();
+
+        let mut iter = map.iter_mut();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.len(), 3);
+    }
+
+    #[test]
+    fn test_index() {
+        let mut map = HashMap::new();
+
+        map.insert(1, 2);
+        map.insert(2, 1);
+        map.insert(3, 4);
+
+        assert_eq!(map[&2], 1);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_index_nonexistent() {
+        let mut map = HashMap::new();
+
+        map.insert(1, 2);
+        map.insert(2, 1);
+        map.insert(3, 4);
+
+        map[&4];
+    }
+
+    #[test]
+    fn test_entry() {
+        let xs = [(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)];
+
+        let mut map: HashMap<_, _> = xs.iter().cloned().collect();
+
+        // Existing key (insert)
+        match map.entry(1) {
+            Vacant(_) => unreachable!(),
+            Occupied(mut view) => {
+                assert_eq!(view.get(), &10);
+                assert_eq!(view.insert(100), 10);
+            }
+        }
+        assert_eq!(map.get(&1).unwrap(), &100);
+        assert_eq!(map.len(), 6);
+
+
+        // Existing key (update)
+        match map.entry(2) {
+            Vacant(_) => unreachable!(),
+            Occupied(mut view) => {
+                let v = view.get_mut();
+                let new_v = (*v) * 10;
+                *v = new_v;
+            }
+        }
+        assert_eq!(map.get(&2).unwrap(), &200);
+        assert_eq!(map.len(), 6);
+
+        // Existing key (take)
+        match map.entry(3) {
+            Vacant(_) => unreachable!(),
+            Occupied(view) => {
+                assert_eq!(view.remove(), 30);
+            }
+        }
+        assert_eq!(map.get(&3), None);
+        assert_eq!(map.len(), 5);
+
+
+        // Inexistent key (insert)
+        match map.entry(10) {
+            Occupied(_) => unreachable!(),
+            Vacant(view) => {
+                assert_eq!(*view.insert(1000), 1000);
+            }
+        }
+        assert_eq!(map.get(&10).unwrap(), &1000);
+        assert_eq!(map.len(), 6);
+    }
+
+    #[test]
+    fn test_entry_take_doesnt_corrupt() {
+        #![allow(deprecated)] //rand
+        // Test for #19292
+        fn check(m: &HashMap<isize, ()>) {
+            for k in m.keys() {
+                assert!(m.contains_key(k),
+                        "{} is in keys() but not in the map?", k);
+            }
+        }
+
+        let mut m = HashMap::new();
+        let mut rng = thread_rng();
+
+        // Populate the map with some items.
+        for _ in 0..50 {
+            let x = rng.gen_range(-10, 10);
+            m.insert(x, ());
+        }
+
+        for i in 0..1000 {
+            let x = rng.gen_range(-10, 10);
+            match m.entry(x) {
+                Vacant(_) => {}
+                Occupied(e) => {
+                    println!("{}: remove {}", i, x);
+                    e.remove();
+                }
+            }
+
+            check(&m);
+        }
+    }
+
+    #[test]
+    fn test_extend_ref() {
+        let mut a = HashMap::new();
+        a.insert(1, "one");
+        let mut b = HashMap::new();
+        b.insert(2, "two");
+        b.insert(3, "three");
+
+        a.extend(&b);
+
+        assert_eq!(a.len(), 3);
+        assert_eq!(a[&1], "one");
+        assert_eq!(a[&2], "two");
+        assert_eq!(a[&3], "three");
+    }
+
+    #[test]
+    fn test_capacity_not_less_than_len() {
+        let mut a = HashMap::new();
+        let mut item = 0;
+
+        for _ in 0..116 {
+            a.insert(item, 0);
+            item += 1;
+        }
+
+        assert!(a.capacity() > a.len());
+
+        let free = a.capacity() - a.len();
+        for _ in 0..free {
+            a.insert(item, 0);
+            item += 1;
+        }
+
+        assert_eq!(a.len(), a.capacity());
+
+        // Insert at capacity should cause allocation.
+        a.insert(item, 0);
+        assert!(a.capacity() > a.len());
+    }
+
+    #[test]
+    fn test_occupied_entry_key() {
+        let mut a = HashMap::new();
+        let key = "hello there";
+        let value = "value goes here";
+        assert!(a.is_empty());
+        a.insert(key.clone(), value.clone());
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+
+        match a.entry(key.clone()) {
+            Vacant(_) => panic!(),
+            Occupied(e) => assert_eq!(key, *e.key()),
+        }
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+    }
+
+    #[test]
+    fn test_vacant_entry_key() {
+        let mut a = HashMap::new();
+        let key = "hello there";
+        let value = "value goes here";
+
+        assert!(a.is_empty());
+        match a.entry(key.clone()) {
+            Occupied(_) => panic!(),
+            Vacant(e) => {
+                assert_eq!(key, *e.key());
+                e.insert(value.clone());
+            }
+        }
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+    }
+}
diff --git a/ctr-std/src/collections/hash/mod.rs b/ctr-std/src/collections/hash/mod.rs
new file mode 100644
index 0000000..7a22bec
--- /dev/null
+++ b/ctr-std/src/collections/hash/mod.rs
@@ -0,0 +1,24 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Unordered containers, implemented as hash-tables
+
+mod bench;
+mod table;
+pub mod map;
+pub mod set;
+
+trait Recover<Q: ?Sized> {
+    type Key;
+
+    fn get(&self, key: &Q) -> Option<&Self::Key>;
+    fn take(&mut self, key: &Q) -> Option<Self::Key>;
+    fn replace(&mut self, key: Self::Key) -> Option<Self::Key>;
+}
diff --git a/ctr-std/src/collections/hash/set.rs b/ctr-std/src/collections/hash/set.rs
new file mode 100644
index 0000000..72af612
--- /dev/null
+++ b/ctr-std/src/collections/hash/set.rs
@@ -0,0 +1,1531 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use borrow::Borrow;
+use fmt;
+use hash::{Hash, BuildHasher};
+use iter::{Chain, FromIterator, FusedIterator};
+use ops::{BitOr, BitAnd, BitXor, Sub};
+
+use super::Recover;
+use super::map::{self, HashMap, Keys, RandomState};
+
+// Future Optimization (FIXME!)
+// =============================
+//
+// Iteration over zero sized values is a noop. There is no need
+// for `bucket.val` in the case of HashSet. I suppose we would need HKT
+// to get rid of it properly.
+
+/// An implementation of a hash set using the underlying representation of a
+/// HashMap where the value is ().
+///
+/// As with the `HashMap` type, a `HashSet` requires that the elements
+/// implement the `Eq` and `Hash` traits. This can frequently be achieved by
+/// using `#[derive(PartialEq, Eq, Hash)]`. If you implement these yourself,
+/// it is important that the following property holds:
+///
+/// ```text
+/// k1 == k2 -> hash(k1) == hash(k2)
+/// ```
+///
+/// In other words, if two keys are equal, their hashes must be equal.
+///
+///
+/// It is a logic error for an item to be modified in such a way that the
+/// item's hash, as determined by the `Hash` trait, or its equality, as
+/// determined by the `Eq` trait, changes while it is in the set. This is
+/// normally only possible through `Cell`, `RefCell`, global state, I/O, or
+/// unsafe code.
+///
+/// # Examples
+///
+/// ```
+/// use std::collections::HashSet;
+/// // Type inference lets us omit an explicit type signature (which
+/// // would be `HashSet<&str>` in this example).
+/// let mut books = HashSet::new();
+///
+/// // Add some books.
+/// books.insert("A Dance With Dragons");
+/// books.insert("To Kill a Mockingbird");
+/// books.insert("The Odyssey");
+/// books.insert("The Great Gatsby");
+///
+/// // Check for a specific one.
+/// if !books.contains("The Winds of Winter") {
+///     println!("We have {} books, but The Winds of Winter ain't one.",
+///              books.len());
+/// }
+///
+/// // Remove a book.
+/// books.remove("The Odyssey");
+///
+/// // Iterate over everything.
+/// for book in &books {
+///     println!("{}", book);
+/// }
+/// ```
+///
+/// The easiest way to use `HashSet` with a custom type is to derive
+/// `Eq` and `Hash`. We must also derive `PartialEq`, this will in the
+/// future be implied by `Eq`.
+///
+/// ```
+/// use std::collections::HashSet;
+/// #[derive(Hash, Eq, PartialEq, Debug)]
+/// struct Viking<'a> {
+///     name: &'a str,
+///     power: usize,
+/// }
+///
+/// let mut vikings = HashSet::new();
+///
+/// vikings.insert(Viking { name: "Einar", power: 9 });
+/// vikings.insert(Viking { name: "Einar", power: 9 });
+/// vikings.insert(Viking { name: "Olaf", power: 4 });
+/// vikings.insert(Viking { name: "Harald", power: 8 });
+///
+/// // Use derived implementation to print the vikings.
+/// for x in &vikings {
+///     println!("{:?}", x);
+/// }
+/// ```
+///
+/// HashSet with fixed list of elements can be initialized from an array:
+///
+/// ```
+/// use std::collections::HashSet;
+///
+/// fn main() {
+///     let viking_names: HashSet<&str> =
+///         [ "Einar", "Olaf", "Harald" ].iter().cloned().collect();
+///     // use the values stored in the set
+/// }
+/// ```
+
+
+#[derive(Clone)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct HashSet<T, S = RandomState> {
+    map: HashMap<T, (), S>,
+}
+
+impl<T: Hash + Eq> HashSet<T, RandomState> {
+    /// Creates an empty HashSet.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let mut set: HashSet<i32> = HashSet::new();
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn new() -> HashSet<T, RandomState> {
+        HashSet { map: HashMap::new() }
+    }
+
+    /// Creates an empty `HashSet` with the specified capacity.
+    ///
+    /// The hash set will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash set will not allocate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let mut set: HashSet<i32> = HashSet::with_capacity(10);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn with_capacity(capacity: usize) -> HashSet<T, RandomState> {
+        HashSet { map: HashMap::with_capacity(capacity) }
+    }
+}
+
+impl<T, S> HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    /// Creates a new empty hash set which will use the given hasher to hash
+    /// keys.
+    ///
+    /// The hash set is also created with the default initial capacity.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow `HashSet`s to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// use std::collections::hash_map::RandomState;
+    ///
+    /// let s = RandomState::new();
+    /// let mut set = HashSet::with_hasher(s);
+    /// set.insert(2);
+    /// ```
+    #[inline]
+    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+    pub fn with_hasher(hasher: S) -> HashSet<T, S> {
+        HashSet { map: HashMap::with_hasher(hasher) }
+    }
+
+    /// Creates an empty HashSet with with the specified capacity, using
+    /// `hasher` to hash the keys.
+    ///
+    /// The hash set will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash set will not allocate.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow `HashSet`s to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// use std::collections::hash_map::RandomState;
+    ///
+    /// let s = RandomState::new();
+    /// let mut set = HashSet::with_capacity_and_hasher(10, s);
+    /// set.insert(1);
+    /// ```
+    #[inline]
+    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
+    pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> HashSet<T, S> {
+        HashSet { map: HashMap::with_capacity_and_hasher(capacity, hasher) }
+    }
+
+    /// Returns a reference to the set's hasher.
+    #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
+    pub fn hasher(&self) -> &S {
+        self.map.hasher()
+    }
+
+    /// Returns the number of elements the set can hold without reallocating.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let set: HashSet<i32> = HashSet::with_capacity(100);
+    /// assert!(set.capacity() >= 100);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn capacity(&self) -> usize {
+        self.map.capacity()
+    }
+
+    /// Reserves capacity for at least `additional` more elements to be inserted
+    /// in the `HashSet`. The collection may reserve more space to avoid
+    /// frequent reallocations.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new allocation size overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let mut set: HashSet<i32> = HashSet::new();
+    /// set.reserve(10);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn reserve(&mut self, additional: usize) {
+        self.map.reserve(additional)
+    }
+
+    /// Shrinks the capacity of the set as much as possible. It will drop
+    /// down as much as possible while maintaining the internal rules
+    /// and possibly leaving some space in accordance with the resize policy.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut set = HashSet::with_capacity(100);
+    /// set.insert(1);
+    /// set.insert(2);
+    /// assert!(set.capacity() >= 100);
+    /// set.shrink_to_fit();
+    /// assert!(set.capacity() >= 2);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn shrink_to_fit(&mut self) {
+        self.map.shrink_to_fit()
+    }
+
+    /// An iterator visiting all elements in arbitrary order.
+    /// Iterator element type is &'a T.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let mut set = HashSet::new();
+    /// set.insert("a");
+    /// set.insert("b");
+    ///
+    /// // Will print in an arbitrary order.
+    /// for x in set.iter() {
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn iter(&self) -> Iter<T> {
+        Iter { iter: self.map.keys() }
+    }
+
+    /// Visit the values representing the difference.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Can be seen as `a - b`.
+    /// for x in a.difference(&b) {
+    ///     println!("{}", x); // Print 1
+    /// }
+    ///
+    /// let diff: HashSet<_> = a.difference(&b).cloned().collect();
+    /// assert_eq!(diff, [1].iter().cloned().collect());
+    ///
+    /// // Note that difference is not symmetric,
+    /// // and `b - a` means something else:
+    /// let diff: HashSet<_> = b.difference(&a).cloned().collect();
+    /// assert_eq!(diff, [4].iter().cloned().collect());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn difference<'a>(&'a self, other: &'a HashSet<T, S>) -> Difference<'a, T, S> {
+        Difference {
+            iter: self.iter(),
+            other: other,
+        }
+    }
+
+    /// Visit the values representing the symmetric difference.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Print 1, 4 in arbitrary order.
+    /// for x in a.symmetric_difference(&b) {
+    ///     println!("{}", x);
+    /// }
+    ///
+    /// let diff1: HashSet<_> = a.symmetric_difference(&b).cloned().collect();
+    /// let diff2: HashSet<_> = b.symmetric_difference(&a).cloned().collect();
+    ///
+    /// assert_eq!(diff1, diff2);
+    /// assert_eq!(diff1, [1, 4].iter().cloned().collect());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn symmetric_difference<'a>(&'a self,
+                                    other: &'a HashSet<T, S>)
+                                    -> SymmetricDifference<'a, T, S> {
+        SymmetricDifference { iter: self.difference(other).chain(other.difference(self)) }
+    }
+
+    /// Visit the values representing the intersection.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Print 2, 3 in arbitrary order.
+    /// for x in a.intersection(&b) {
+    ///     println!("{}", x);
+    /// }
+    ///
+    /// let intersection: HashSet<_> = a.intersection(&b).cloned().collect();
+    /// assert_eq!(intersection, [2, 3].iter().cloned().collect());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn intersection<'a>(&'a self, other: &'a HashSet<T, S>) -> Intersection<'a, T, S> {
+        Intersection {
+            iter: self.iter(),
+            other: other,
+        }
+    }
+
+    /// Visit the values representing the union.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Print 1, 2, 3, 4 in arbitrary order.
+    /// for x in a.union(&b) {
+    ///     println!("{}", x);
+    /// }
+    ///
+    /// let union: HashSet<_> = a.union(&b).cloned().collect();
+    /// assert_eq!(union, [1, 2, 3, 4].iter().cloned().collect());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn union<'a>(&'a self, other: &'a HashSet<T, S>) -> Union<'a, T, S> {
+        Union { iter: self.iter().chain(other.difference(self)) }
+    }
+
+    /// Returns the number of elements in the set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut v = HashSet::new();
+    /// assert_eq!(v.len(), 0);
+    /// v.insert(1);
+    /// assert_eq!(v.len(), 1);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn len(&self) -> usize {
+        self.map.len()
+    }
+
+    /// Returns true if the set contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut v = HashSet::new();
+    /// assert!(v.is_empty());
+    /// v.insert(1);
+    /// assert!(!v.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_empty(&self) -> bool {
+        self.map.is_empty()
+    }
+
+    /// Clears the set, returning all elements in an iterator.
+    #[inline]
+    #[stable(feature = "drain", since = "1.6.0")]
+    pub fn drain(&mut self) -> Drain<T> {
+        Drain { iter: self.map.drain() }
+    }
+
+    /// Clears the set, removing all values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut v = HashSet::new();
+    /// v.insert(1);
+    /// v.clear();
+    /// assert!(v.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn clear(&mut self) {
+        self.map.clear()
+    }
+
+    /// Returns `true` if the set contains a value.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the value type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert_eq!(set.contains(&1), true);
+    /// assert_eq!(set.contains(&4), false);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
+        where T: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        self.map.contains_key(value)
+    }
+
+    /// Returns a reference to the value in the set, if any, that is equal to the given value.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the value type.
+    #[stable(feature = "set_recovery", since = "1.9.0")]
+    pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
+        where T: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        Recover::get(&self.map, value)
+    }
+
+    /// Returns `true` if the set has no elements in common with `other`.
+    /// This is equivalent to checking for an empty intersection.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let mut b = HashSet::new();
+    ///
+    /// assert_eq!(a.is_disjoint(&b), true);
+    /// b.insert(4);
+    /// assert_eq!(a.is_disjoint(&b), true);
+    /// b.insert(1);
+    /// assert_eq!(a.is_disjoint(&b), false);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_disjoint(&self, other: &HashSet<T, S>) -> bool {
+        self.iter().all(|v| !other.contains(v))
+    }
+
+    /// Returns `true` if the set is a subset of another.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let sup: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let mut set = HashSet::new();
+    ///
+    /// assert_eq!(set.is_subset(&sup), true);
+    /// set.insert(2);
+    /// assert_eq!(set.is_subset(&sup), true);
+    /// set.insert(4);
+    /// assert_eq!(set.is_subset(&sup), false);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_subset(&self, other: &HashSet<T, S>) -> bool {
+        self.iter().all(|v| other.contains(v))
+    }
+
+    /// Returns `true` if the set is a superset of another.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let sub: HashSet<_> = [1, 2].iter().cloned().collect();
+    /// let mut set = HashSet::new();
+    ///
+    /// assert_eq!(set.is_superset(&sub), false);
+    ///
+    /// set.insert(0);
+    /// set.insert(1);
+    /// assert_eq!(set.is_superset(&sub), false);
+    ///
+    /// set.insert(2);
+    /// assert_eq!(set.is_superset(&sub), true);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_superset(&self, other: &HashSet<T, S>) -> bool {
+        other.is_subset(self)
+    }
+
+    /// Adds a value to the set.
+    ///
+    /// If the set did not have this value present, `true` is returned.
+    ///
+    /// If the set did have this value present, `false` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut set = HashSet::new();
+    ///
+    /// assert_eq!(set.insert(2), true);
+    /// assert_eq!(set.insert(2), false);
+    /// assert_eq!(set.len(), 1);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn insert(&mut self, value: T) -> bool {
+        self.map.insert(value, ()).is_none()
+    }
+
+    /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
+    /// one. Returns the replaced value.
+    #[stable(feature = "set_recovery", since = "1.9.0")]
+    pub fn replace(&mut self, value: T) -> Option<T> {
+        Recover::replace(&mut self.map, value)
+    }
+
+    /// Removes a value from the set. Returns `true` if the value was
+    /// present in the set.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the value type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut set = HashSet::new();
+    ///
+    /// set.insert(2);
+    /// assert_eq!(set.remove(&2), true);
+    /// assert_eq!(set.remove(&2), false);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
+        where T: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        self.map.remove(value).is_some()
+    }
+
+    /// Removes and returns the value in the set, if any, that is equal to the given one.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the value type.
+    #[stable(feature = "set_recovery", since = "1.9.0")]
+    pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
+        where T: Borrow<Q>,
+              Q: Hash + Eq
+    {
+        Recover::take(&mut self.map, value)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, S> PartialEq for HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    fn eq(&self, other: &HashSet<T, S>) -> bool {
+        if self.len() != other.len() {
+            return false;
+        }
+
+        self.iter().all(|key| other.contains(key))
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, S> Eq for HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, S> fmt::Debug for HashSet<T, S>
+    where T: Eq + Hash + fmt::Debug,
+          S: BuildHasher
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_set().entries(self.iter()).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, S> FromIterator<T> for HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher + Default
+{
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> HashSet<T, S> {
+        let mut set = HashSet::with_hasher(Default::default());
+        set.extend(iter);
+        set
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, S> Extend<T> for HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        self.map.extend(iter.into_iter().map(|k| (k, ())));
+    }
+}
+
+#[stable(feature = "hash_extend_copy", since = "1.4.0")]
+impl<'a, T, S> Extend<&'a T> for HashSet<T, S>
+    where T: 'a + Eq + Hash + Copy,
+          S: BuildHasher
+{
+    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().cloned());
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, S> Default for HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher + Default
+{
+    /// Creates an empty `HashSet<T, S>` with the `Default` value for the hasher.
+    fn default() -> HashSet<T, S> {
+        HashSet { map: HashMap::default() }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, 'b, T, S> BitOr<&'b HashSet<T, S>> for &'a HashSet<T, S>
+    where T: Eq + Hash + Clone,
+          S: BuildHasher + Default
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the union of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
+    ///
+    /// let set = &a | &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [1, 2, 3, 4, 5];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn bitor(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
+        self.union(rhs).cloned().collect()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, 'b, T, S> BitAnd<&'b HashSet<T, S>> for &'a HashSet<T, S>
+    where T: Eq + Hash + Clone,
+          S: BuildHasher + Default
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the intersection of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![2, 3, 4].into_iter().collect();
+    ///
+    /// let set = &a & &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [2, 3];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn bitand(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
+        self.intersection(rhs).cloned().collect()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, 'b, T, S> BitXor<&'b HashSet<T, S>> for &'a HashSet<T, S>
+    where T: Eq + Hash + Clone,
+          S: BuildHasher + Default
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the symmetric difference of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
+    ///
+    /// let set = &a ^ &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [1, 2, 4, 5];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn bitxor(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
+        self.symmetric_difference(rhs).cloned().collect()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, 'b, T, S> Sub<&'b HashSet<T, S>> for &'a HashSet<T, S>
+    where T: Eq + Hash + Clone,
+          S: BuildHasher + Default
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the difference of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
+    ///
+    /// let set = &a - &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [1, 2];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn sub(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
+        self.difference(rhs).cloned().collect()
+    }
+}
+
+/// HashSet iterator
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Iter<'a, K: 'a> {
+    iter: Keys<'a, K, ()>,
+}
+
+/// HashSet move iterator
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct IntoIter<K> {
+    iter: map::IntoIter<K, ()>,
+}
+
+/// HashSet drain iterator
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Drain<'a, K: 'a> {
+    iter: map::Drain<'a, K, ()>,
+}
+
+/// Intersection iterator
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Intersection<'a, T: 'a, S: 'a> {
+    // iterator of the first set
+    iter: Iter<'a, T>,
+    // the second set
+    other: &'a HashSet<T, S>,
+}
+
+/// Difference iterator
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Difference<'a, T: 'a, S: 'a> {
+    // iterator of the first set
+    iter: Iter<'a, T>,
+    // the second set
+    other: &'a HashSet<T, S>,
+}
+
+/// Symmetric difference iterator.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct SymmetricDifference<'a, T: 'a, S: 'a> {
+    iter: Chain<Difference<'a, T, S>, Difference<'a, T, S>>,
+}
+
+/// Set union iterator.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Union<'a, T: 'a, S: 'a> {
+    iter: Chain<Iter<'a, T>, Difference<'a, T, S>>,
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> IntoIterator for &'a HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Iter<'a, T> {
+        self.iter()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, S> IntoIterator for HashSet<T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    /// Creates a consuming iterator, that is, one that moves each value out
+    /// of the set in arbitrary order. The set cannot be used after calling
+    /// this.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    /// let mut set = HashSet::new();
+    /// set.insert("a".to_string());
+    /// set.insert("b".to_string());
+    ///
+    /// // Not possible to collect to a Vec<String> with a regular `.iter()`.
+    /// let v: Vec<String> = set.into_iter().collect();
+    ///
+    /// // Will print in an arbitrary order.
+    /// for x in &v {
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    fn into_iter(self) -> IntoIter<T> {
+        IntoIter { iter: self.map.into_iter() }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K> Clone for Iter<'a, K> {
+    fn clone(&self) -> Iter<'a, K> {
+        Iter { iter: self.iter.clone() }
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K> Iterator for Iter<'a, K> {
+    type Item = &'a K;
+
+    fn next(&mut self) -> Option<&'a K> {
+        self.iter.next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K> ExactSizeIterator for Iter<'a, K> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K> FusedIterator for Iter<'a, K> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K> Iterator for IntoIter<K> {
+    type Item = K;
+
+    fn next(&mut self) -> Option<K> {
+        self.iter.next().map(|(k, _)| k)
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<K> ExactSizeIterator for IntoIter<K> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<K> FusedIterator for IntoIter<K> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K> Iterator for Drain<'a, K> {
+    type Item = K;
+
+    fn next(&mut self) -> Option<K> {
+        self.iter.next().map(|(k, _)| k)
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, K> ExactSizeIterator for Drain<'a, K> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K> FusedIterator for Drain<'a, K> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Clone for Intersection<'a, T, S> {
+    fn clone(&self) -> Intersection<'a, T, S> {
+        Intersection { iter: self.iter.clone(), ..*self }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Iterator for Intersection<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<&'a T> {
+        loop {
+            match self.iter.next() {
+                None => return None,
+                Some(elt) => {
+                    if self.other.contains(elt) {
+                        return Some(elt);
+                    }
+                }
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, upper) = self.iter.size_hint();
+        (0, upper)
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T, S> FusedIterator for Intersection<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Clone for Difference<'a, T, S> {
+    fn clone(&self) -> Difference<'a, T, S> {
+        Difference { iter: self.iter.clone(), ..*self }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Iterator for Difference<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<&'a T> {
+        loop {
+            match self.iter.next() {
+                None => return None,
+                Some(elt) => {
+                    if !self.other.contains(elt) {
+                        return Some(elt);
+                    }
+                }
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, upper) = self.iter.size_hint();
+        (0, upper)
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T, S> FusedIterator for Difference<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Clone for SymmetricDifference<'a, T, S> {
+    fn clone(&self) -> SymmetricDifference<'a, T, S> {
+        SymmetricDifference { iter: self.iter.clone() }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Iterator for SymmetricDifference<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<&'a T> {
+        self.iter.next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T, S> FusedIterator for SymmetricDifference<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Clone for Union<'a, T, S> {
+    fn clone(&self) -> Union<'a, T, S> {
+        Union { iter: self.iter.clone() }
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T, S> FusedIterator for Union<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T, S> Iterator for Union<'a, T, S>
+    where T: Eq + Hash,
+          S: BuildHasher
+{
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<&'a T> {
+        self.iter.next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[allow(dead_code)]
+fn assert_covariance() {
+    fn set<'new>(v: HashSet<&'static str>) -> HashSet<&'new str> {
+        v
+    }
+    fn iter<'a, 'new>(v: Iter<'a, &'static str>) -> Iter<'a, &'new str> {
+        v
+    }
+    fn into_iter<'new>(v: IntoIter<&'static str>) -> IntoIter<&'new str> {
+        v
+    }
+    fn difference<'a, 'new>(v: Difference<'a, &'static str, RandomState>)
+                            -> Difference<'a, &'new str, RandomState> {
+        v
+    }
+    fn symmetric_difference<'a, 'new>(v: SymmetricDifference<'a, &'static str, RandomState>)
+                                      -> SymmetricDifference<'a, &'new str, RandomState> {
+        v
+    }
+    fn intersection<'a, 'new>(v: Intersection<'a, &'static str, RandomState>)
+                              -> Intersection<'a, &'new str, RandomState> {
+        v
+    }
+    fn union<'a, 'new>(v: Union<'a, &'static str, RandomState>)
+                       -> Union<'a, &'new str, RandomState> {
+        v
+    }
+    fn drain<'new>(d: Drain<'static, &'static str>) -> Drain<'new, &'new str> {
+        d
+    }
+}
+
+#[cfg(test)]
+mod test_set {
+    use super::HashSet;
+    use super::super::map::RandomState;
+
+    #[test]
+    fn test_zero_capacities() {
+        type HS = HashSet<i32>;
+
+        let s = HS::new();
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::default();
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::with_hasher(RandomState::new());
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::with_capacity(0);
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::with_capacity_and_hasher(0, RandomState::new());
+        assert_eq!(s.capacity(), 0);
+
+        let mut s = HS::new();
+        s.insert(1);
+        s.insert(2);
+        s.remove(&1);
+        s.remove(&2);
+        s.shrink_to_fit();
+        assert_eq!(s.capacity(), 0);
+
+        let mut s = HS::new();
+        s.reserve(0);
+        assert_eq!(s.capacity(), 0);
+    }
+
+    #[test]
+    fn test_disjoint() {
+        let mut xs = HashSet::new();
+        let mut ys = HashSet::new();
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(xs.insert(5));
+        assert!(ys.insert(11));
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(xs.insert(7));
+        assert!(xs.insert(19));
+        assert!(xs.insert(4));
+        assert!(ys.insert(2));
+        assert!(ys.insert(-11));
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(ys.insert(7));
+        assert!(!xs.is_disjoint(&ys));
+        assert!(!ys.is_disjoint(&xs));
+    }
+
+    #[test]
+    fn test_subset_and_superset() {
+        let mut a = HashSet::new();
+        assert!(a.insert(0));
+        assert!(a.insert(5));
+        assert!(a.insert(11));
+        assert!(a.insert(7));
+
+        let mut b = HashSet::new();
+        assert!(b.insert(0));
+        assert!(b.insert(7));
+        assert!(b.insert(19));
+        assert!(b.insert(250));
+        assert!(b.insert(11));
+        assert!(b.insert(200));
+
+        assert!(!a.is_subset(&b));
+        assert!(!a.is_superset(&b));
+        assert!(!b.is_subset(&a));
+        assert!(!b.is_superset(&a));
+
+        assert!(b.insert(5));
+
+        assert!(a.is_subset(&b));
+        assert!(!a.is_superset(&b));
+        assert!(!b.is_subset(&a));
+        assert!(b.is_superset(&a));
+    }
+
+    #[test]
+    fn test_iterate() {
+        let mut a = HashSet::new();
+        for i in 0..32 {
+            assert!(a.insert(i));
+        }
+        let mut observed: u32 = 0;
+        for k in &a {
+            observed |= 1 << *k;
+        }
+        assert_eq!(observed, 0xFFFF_FFFF);
+    }
+
+    #[test]
+    fn test_intersection() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(11));
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(77));
+        assert!(a.insert(103));
+        assert!(a.insert(5));
+        assert!(a.insert(-5));
+
+        assert!(b.insert(2));
+        assert!(b.insert(11));
+        assert!(b.insert(77));
+        assert!(b.insert(-9));
+        assert!(b.insert(-42));
+        assert!(b.insert(5));
+        assert!(b.insert(3));
+
+        let mut i = 0;
+        let expected = [3, 5, 11, 77];
+        for x in a.intersection(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_difference() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+
+        assert!(b.insert(3));
+        assert!(b.insert(9));
+
+        let mut i = 0;
+        let expected = [1, 5, 11];
+        for x in a.difference(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_symmetric_difference() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+
+        assert!(b.insert(-2));
+        assert!(b.insert(3));
+        assert!(b.insert(9));
+        assert!(b.insert(14));
+        assert!(b.insert(22));
+
+        let mut i = 0;
+        let expected = [-2, 1, 5, 11, 14, 22];
+        for x in a.symmetric_difference(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_union() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+        assert!(a.insert(16));
+        assert!(a.insert(19));
+        assert!(a.insert(24));
+
+        assert!(b.insert(-2));
+        assert!(b.insert(1));
+        assert!(b.insert(5));
+        assert!(b.insert(9));
+        assert!(b.insert(13));
+        assert!(b.insert(19));
+
+        let mut i = 0;
+        let expected = [-2, 1, 3, 5, 9, 11, 13, 16, 19, 24];
+        for x in a.union(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_from_iter() {
+        let xs = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+
+        let set: HashSet<_> = xs.iter().cloned().collect();
+
+        for x in &xs {
+            assert!(set.contains(x));
+        }
+    }
+
+    #[test]
+    fn test_move_iter() {
+        let hs = {
+            let mut hs = HashSet::new();
+
+            hs.insert('a');
+            hs.insert('b');
+
+            hs
+        };
+
+        let v = hs.into_iter().collect::<Vec<char>>();
+        assert!(v == ['a', 'b'] || v == ['b', 'a']);
+    }
+
+    #[test]
+    fn test_eq() {
+        // These constants once happened to expose a bug in insert().
+        // I'm keeping them around to prevent a regression.
+        let mut s1 = HashSet::new();
+
+        s1.insert(1);
+        s1.insert(2);
+        s1.insert(3);
+
+        let mut s2 = HashSet::new();
+
+        s2.insert(1);
+        s2.insert(2);
+
+        assert!(s1 != s2);
+
+        s2.insert(3);
+
+        assert_eq!(s1, s2);
+    }
+
+    #[test]
+    fn test_show() {
+        let mut set = HashSet::new();
+        let empty = HashSet::<i32>::new();
+
+        set.insert(1);
+        set.insert(2);
+
+        let set_str = format!("{:?}", set);
+
+        assert!(set_str == "{1, 2}" || set_str == "{2, 1}");
+        assert_eq!(format!("{:?}", empty), "{}");
+    }
+
+    #[test]
+    fn test_trivial_drain() {
+        let mut s = HashSet::<i32>::new();
+        for _ in s.drain() {}
+        assert!(s.is_empty());
+        drop(s);
+
+        let mut s = HashSet::<i32>::new();
+        drop(s.drain());
+        assert!(s.is_empty());
+    }
+
+    #[test]
+    fn test_drain() {
+        let mut s: HashSet<_> = (1..100).collect();
+
+        // try this a bunch of times to make sure we don't screw up internal state.
+        for _ in 0..20 {
+            assert_eq!(s.len(), 99);
+
+            {
+                let mut last_i = 0;
+                let mut d = s.drain();
+                for (i, x) in d.by_ref().take(50).enumerate() {
+                    last_i = i;
+                    assert!(x != 0);
+                }
+                assert_eq!(last_i, 49);
+            }
+
+            for _ in &s {
+                panic!("s should be empty!");
+            }
+
+            // reset to try again.
+            s.extend(1..100);
+        }
+    }
+
+    #[test]
+    fn test_replace() {
+        use hash;
+
+        #[derive(Debug)]
+        struct Foo(&'static str, i32);
+
+        impl PartialEq for Foo {
+            fn eq(&self, other: &Self) -> bool {
+                self.0 == other.0
+            }
+        }
+
+        impl Eq for Foo {}
+
+        impl hash::Hash for Foo {
+            fn hash<H: hash::Hasher>(&self, h: &mut H) {
+                self.0.hash(h);
+            }
+        }
+
+        let mut s = HashSet::new();
+        assert_eq!(s.replace(Foo("a", 1)), None);
+        assert_eq!(s.len(), 1);
+        assert_eq!(s.replace(Foo("a", 2)), Some(Foo("a", 1)));
+        assert_eq!(s.len(), 1);
+
+        let mut it = s.iter();
+        assert_eq!(it.next(), Some(&Foo("a", 2)));
+        assert_eq!(it.next(), None);
+    }
+
+    #[test]
+    fn test_extend_ref() {
+        let mut a = HashSet::new();
+        a.insert(1);
+
+        a.extend(&[2, 3, 4]);
+
+        assert_eq!(a.len(), 4);
+        assert!(a.contains(&1));
+        assert!(a.contains(&2));
+        assert!(a.contains(&3));
+        assert!(a.contains(&4));
+
+        let mut b = HashSet::new();
+        b.insert(5);
+        b.insert(6);
+
+        a.extend(&b);
+
+        assert_eq!(a.len(), 6);
+        assert!(a.contains(&1));
+        assert!(a.contains(&2));
+        assert!(a.contains(&3));
+        assert!(a.contains(&4));
+        assert!(a.contains(&5));
+        assert!(a.contains(&6));
+    }
+}
diff --git a/ctr-std/src/collections/hash/table.rs b/ctr-std/src/collections/hash/table.rs
new file mode 100644
index 0000000..4fd4abf
--- /dev/null
+++ b/ctr-std/src/collections/hash/table.rs
@@ -0,0 +1,1071 @@
+// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(deprecated)]
+
+use alloc::heap::{EMPTY, allocate, deallocate};
+
+use cmp;
+use hash::{BuildHasher, Hash, Hasher};
+use intrinsics::needs_drop;
+use marker;
+use mem::{align_of, size_of};
+use mem;
+use ops::{Deref, DerefMut};
+use ptr::{self, Unique, Shared};
+
+use self::BucketState::*;
+
+/// Integer type used for stored hash values.
+///
+/// No more than bit_width(usize) bits are needed to select a bucket.
+///
+/// The most significant bit is ours to use for tagging `SafeHash`.
+///
+/// (Even if we could have usize::MAX bytes allocated for buckets,
+/// each bucket stores at least a `HashUint`, so there can be no more than
+/// usize::MAX / size_of(usize) buckets.)
+type HashUint = usize;
+
+const EMPTY_BUCKET: HashUint = 0;
+
+/// The raw hashtable, providing safe-ish access to the unzipped and highly
+/// optimized arrays of hashes, and key-value pairs.
+///
+/// This design is a lot faster than the naive
+/// `Vec<Option<(u64, K, V)>>`, because we don't pay for the overhead of an
+/// option on every element, and we get a generally more cache-aware design.
+///
+/// Essential invariants of this structure:
+///
+///   - if t.hashes[i] == EMPTY_BUCKET, then `Bucket::at_index(&t, i).raw`
+///     points to 'undefined' contents. Don't read from it. This invariant is
+///     enforced outside this module with the `EmptyBucket`, `FullBucket`,
+///     and `SafeHash` types.
+///
+///   - An `EmptyBucket` is only constructed at an index with
+///     a hash of EMPTY_BUCKET.
+///
+///   - A `FullBucket` is only constructed at an index with a
+///     non-EMPTY_BUCKET hash.
+///
+///   - A `SafeHash` is only constructed for non-`EMPTY_BUCKET` hash. We get
+///     around hashes of zero by changing them to 0x8000_0000_0000_0000,
+///     which will likely map to the same bucket, while not being confused
+///     with "empty".
+///
+///   - Both "arrays represented by pointers" are the same length:
+///     `capacity`. This is set at creation and never changes. The arrays
+///     are unzipped and are more cache aware (scanning through 8 hashes
+///     brings in at most 2 cache lines, since they're all right beside each
+///     other). This layout may waste space in padding such as in a map from
+///     u64 to u8, but is a more cache conscious layout as the key-value pairs
+///     are only very shortly probed and the desired value will be in the same
+///     or next cache line.
+///
+/// You can kind of think of this module/data structure as a safe wrapper
+/// around just the "table" part of the hashtable. It enforces some
+/// invariants at the type level and employs some performance trickery,
+/// but in general is just a tricked out `Vec<Option<(u64, K, V)>>`.
+pub struct RawTable<K, V> {
+    capacity: usize,
+    size: usize,
+    hashes: Unique<HashUint>,
+
+    // Because K/V do not appear directly in any of the types in the struct,
+    // inform rustc that in fact instances of K and V are reachable from here.
+    marker: marker::PhantomData<(K, V)>,
+}
+
+unsafe impl<K: Send, V: Send> Send for RawTable<K, V> {}
+unsafe impl<K: Sync, V: Sync> Sync for RawTable<K, V> {}
+
+struct RawBucket<K, V> {
+    hash: *mut HashUint,
+    // We use *const to ensure covariance with respect to K and V
+    pair: *const (K, V),
+    _marker: marker::PhantomData<(K, V)>,
+}
+
+impl<K, V> Copy for RawBucket<K, V> {}
+impl<K, V> Clone for RawBucket<K, V> {
+    fn clone(&self) -> RawBucket<K, V> {
+        *self
+    }
+}
+
+pub struct Bucket<K, V, M> {
+    raw: RawBucket<K, V>,
+    idx: usize,
+    table: M,
+}
+
+impl<K, V, M: Copy> Copy for Bucket<K, V, M> {}
+impl<K, V, M: Copy> Clone for Bucket<K, V, M> {
+    fn clone(&self) -> Bucket<K, V, M> {
+        *self
+    }
+}
+
+pub struct EmptyBucket<K, V, M> {
+    raw: RawBucket<K, V>,
+    idx: usize,
+    table: M,
+}
+
+pub struct FullBucket<K, V, M> {
+    raw: RawBucket<K, V>,
+    idx: usize,
+    table: M,
+}
+
+pub type FullBucketMut<'table, K, V> = FullBucket<K, V, &'table mut RawTable<K, V>>;
+
+pub enum BucketState<K, V, M> {
+    Empty(EmptyBucket<K, V, M>),
+    Full(FullBucket<K, V, M>),
+}
+
+// A GapThenFull encapsulates the state of two consecutive buckets at once.
+// The first bucket, called the gap, is known to be empty.
+// The second bucket is full.
+pub struct GapThenFull<K, V, M> {
+    gap: EmptyBucket<K, V, ()>,
+    full: FullBucket<K, V, M>,
+}
+
+/// A hash that is not zero, since we use a hash of zero to represent empty
+/// buckets.
+#[derive(PartialEq, Copy, Clone)]
+pub struct SafeHash {
+    hash: HashUint,
+}
+
+impl SafeHash {
+    /// Peek at the hash value, which is guaranteed to be non-zero.
+    #[inline(always)]
+    pub fn inspect(&self) -> HashUint {
+        self.hash
+    }
+
+    #[inline(always)]
+    pub fn new(hash: u64) -> Self {
+        // We need to avoid 0 in order to prevent collisions with
+        // EMPTY_HASH. We can maintain our precious uniform distribution
+        // of initial indexes by unconditionally setting the MSB,
+        // effectively reducing the hashes by one bit.
+        //
+        // Truncate hash to fit in `HashUint`.
+        let hash_bits = size_of::<HashUint>() * 8;
+        SafeHash { hash: (1 << (hash_bits - 1)) | (hash as HashUint) }
+    }
+}
+
+/// We need to remove hashes of 0. That's reserved for empty buckets.
+/// This function wraps up `hash_keyed` to be the only way outside this
+/// module to generate a SafeHash.
+pub fn make_hash<T: ?Sized, S>(hash_state: &S, t: &T) -> SafeHash
+    where T: Hash,
+          S: BuildHasher
+{
+    let mut state = hash_state.build_hasher();
+    t.hash(&mut state);
+    SafeHash::new(state.finish())
+}
+
+// `replace` casts a `*HashUint` to a `*SafeHash`. Since we statically
+// ensure that a `FullBucket` points to an index with a non-zero hash,
+// and a `SafeHash` is just a `HashUint` with a different name, this is
+// safe.
+//
+// This test ensures that a `SafeHash` really IS the same size as a
+// `HashUint`. If you need to change the size of `SafeHash` (and
+// consequently made this test fail), `replace` needs to be
+// modified to no longer assume this.
+#[test]
+fn can_alias_safehash_as_hash() {
+    assert_eq!(size_of::<SafeHash>(), size_of::<HashUint>())
+}
+
+impl<K, V> RawBucket<K, V> {
+    unsafe fn offset(self, count: isize) -> RawBucket<K, V> {
+        RawBucket {
+            hash: self.hash.offset(count),
+            pair: self.pair.offset(count),
+            _marker: marker::PhantomData,
+        }
+    }
+}
+
+// Buckets hold references to the table.
+impl<K, V, M> FullBucket<K, V, M> {
+    /// Borrow a reference to the table.
+    pub fn table(&self) -> &M {
+        &self.table
+    }
+    /// Move out the reference to the table.
+    pub fn into_table(self) -> M {
+        self.table
+    }
+    /// Get the raw index.
+    pub fn index(&self) -> usize {
+        self.idx
+    }
+}
+
+impl<K, V, M> EmptyBucket<K, V, M> {
+    /// Borrow a reference to the table.
+    pub fn table(&self) -> &M {
+        &self.table
+    }
+}
+
+impl<K, V, M> Bucket<K, V, M> {
+    /// Get the raw index.
+    pub fn index(&self) -> usize {
+        self.idx
+    }
+}
+
+impl<K, V, M> Deref for FullBucket<K, V, M>
+    where M: Deref<Target = RawTable<K, V>>
+{
+    type Target = RawTable<K, V>;
+    fn deref(&self) -> &RawTable<K, V> {
+        &self.table
+    }
+}
+
+/// `Put` is implemented for types which provide access to a table and cannot be invalidated
+///  by filling a bucket. A similar implementation for `Take` is possible.
+pub trait Put<K, V> {
+    unsafe fn borrow_table_mut(&mut self) -> &mut RawTable<K, V>;
+}
+
+
+impl<'t, K, V> Put<K, V> for &'t mut RawTable<K, V> {
+    unsafe fn borrow_table_mut(&mut self) -> &mut RawTable<K, V> {
+        *self
+    }
+}
+
+impl<K, V, M> Put<K, V> for Bucket<K, V, M>
+    where M: Put<K, V>
+{
+    unsafe fn borrow_table_mut(&mut self) -> &mut RawTable<K, V> {
+        self.table.borrow_table_mut()
+    }
+}
+
+impl<K, V, M> Put<K, V> for FullBucket<K, V, M>
+    where M: Put<K, V>
+{
+    unsafe fn borrow_table_mut(&mut self) -> &mut RawTable<K, V> {
+        self.table.borrow_table_mut()
+    }
+}
+
+impl<K, V, M: Deref<Target = RawTable<K, V>>> Bucket<K, V, M> {
+    pub fn new(table: M, hash: SafeHash) -> Bucket<K, V, M> {
+        Bucket::at_index(table, hash.inspect() as usize)
+    }
+
+    pub fn at_index(table: M, ib_index: usize) -> Bucket<K, V, M> {
+        // if capacity is 0, then the RawBucket will be populated with bogus pointers.
+        // This is an uncommon case though, so avoid it in release builds.
+        debug_assert!(table.capacity() > 0,
+                      "Table should have capacity at this point");
+        let ib_index = ib_index & (table.capacity() - 1);
+        Bucket {
+            raw: unsafe { table.first_bucket_raw().offset(ib_index as isize) },
+            idx: ib_index,
+            table: table,
+        }
+    }
+
+    pub fn first(table: M) -> Bucket<K, V, M> {
+        Bucket {
+            raw: table.first_bucket_raw(),
+            idx: 0,
+            table: table,
+        }
+    }
+
+    /// Reads a bucket at a given index, returning an enum indicating whether
+    /// it's initialized or not. You need to match on this enum to get
+    /// the appropriate types to call most of the other functions in
+    /// this module.
+    pub fn peek(self) -> BucketState<K, V, M> {
+        match unsafe { *self.raw.hash } {
+            EMPTY_BUCKET => {
+                Empty(EmptyBucket {
+                    raw: self.raw,
+                    idx: self.idx,
+                    table: self.table,
+                })
+            }
+            _ => {
+                Full(FullBucket {
+                    raw: self.raw,
+                    idx: self.idx,
+                    table: self.table,
+                })
+            }
+        }
+    }
+
+    /// Modifies the bucket pointer in place to make it point to the next slot.
+    pub fn next(&mut self) {
+        self.idx += 1;
+        let range = self.table.capacity();
+        // This code is branchless thanks to a conditional move.
+        let dist = if self.idx & (range - 1) == 0 {
+            1 - range as isize
+        } else {
+            1
+        };
+        unsafe {
+            self.raw = self.raw.offset(dist);
+        }
+    }
+}
+
+impl<K, V, M: Deref<Target = RawTable<K, V>>> EmptyBucket<K, V, M> {
+    #[inline]
+    pub fn next(self) -> Bucket<K, V, M> {
+        let mut bucket = self.into_bucket();
+        bucket.next();
+        bucket
+    }
+
+    #[inline]
+    pub fn into_bucket(self) -> Bucket<K, V, M> {
+        Bucket {
+            raw: self.raw,
+            idx: self.idx,
+            table: self.table,
+        }
+    }
+
+    pub fn gap_peek(self) -> Option<GapThenFull<K, V, M>> {
+        let gap = EmptyBucket {
+            raw: self.raw,
+            idx: self.idx,
+            table: (),
+        };
+
+        match self.next().peek() {
+            Full(bucket) => {
+                Some(GapThenFull {
+                    gap: gap,
+                    full: bucket,
+                })
+            }
+            Empty(..) => None,
+        }
+    }
+}
+
+impl<K, V, M> EmptyBucket<K, V, M>
+    where M: Put<K, V>
+{
+    /// Puts given key and value pair, along with the key's hash,
+    /// into this bucket in the hashtable. Note how `self` is 'moved' into
+    /// this function, because this slot will no longer be empty when
+    /// we return! A `FullBucket` is returned for later use, pointing to
+    /// the newly-filled slot in the hashtable.
+    ///
+    /// Use `make_hash` to construct a `SafeHash` to pass to this function.
+    pub fn put(mut self, hash: SafeHash, key: K, value: V) -> FullBucket<K, V, M> {
+        unsafe {
+            *self.raw.hash = hash.inspect();
+            ptr::write(self.raw.pair as *mut (K, V), (key, value));
+
+            self.table.borrow_table_mut().size += 1;
+        }
+
+        FullBucket {
+            raw: self.raw,
+            idx: self.idx,
+            table: self.table,
+        }
+    }
+}
+
+impl<K, V, M: Deref<Target = RawTable<K, V>>> FullBucket<K, V, M> {
+    #[inline]
+    pub fn next(self) -> Bucket<K, V, M> {
+        let mut bucket = self.into_bucket();
+        bucket.next();
+        bucket
+    }
+
+    #[inline]
+    pub fn into_bucket(self) -> Bucket<K, V, M> {
+        Bucket {
+            raw: self.raw,
+            idx: self.idx,
+            table: self.table,
+        }
+    }
+
+    /// Duplicates the current position. This can be useful for operations
+    /// on two or more buckets.
+    pub fn stash(self) -> FullBucket<K, V, Self> {
+        FullBucket {
+            raw: self.raw,
+            idx: self.idx,
+            table: self,
+        }
+    }
+
+    /// Get the distance between this bucket and the 'ideal' location
+    /// as determined by the key's hash stored in it.
+    ///
+    /// In the cited blog posts above, this is called the "distance to
+    /// initial bucket", or DIB. Also known as "probe count".
+    pub fn displacement(&self) -> usize {
+        // Calculates the distance one has to travel when going from
+        // `hash mod capacity` onwards to `idx mod capacity`, wrapping around
+        // if the destination is not reached before the end of the table.
+        (self.idx.wrapping_sub(self.hash().inspect() as usize)) & (self.table.capacity() - 1)
+    }
+
+    #[inline]
+    pub fn hash(&self) -> SafeHash {
+        unsafe { SafeHash { hash: *self.raw.hash } }
+    }
+
+    /// Gets references to the key and value at a given index.
+    pub fn read(&self) -> (&K, &V) {
+        unsafe { (&(*self.raw.pair).0, &(*self.raw.pair).1) }
+    }
+}
+
+// We take a mutable reference to the table instead of accepting anything that
+// implements `DerefMut` to prevent fn `take` from being called on `stash`ed
+// buckets.
+impl<'t, K, V> FullBucket<K, V, &'t mut RawTable<K, V>> {
+    /// Removes this bucket's key and value from the hashtable.
+    ///
+    /// This works similarly to `put`, building an `EmptyBucket` out of the
+    /// taken bucket.
+    pub fn take(mut self) -> (EmptyBucket<K, V, &'t mut RawTable<K, V>>, K, V) {
+        self.table.size -= 1;
+
+        unsafe {
+            *self.raw.hash = EMPTY_BUCKET;
+            let (k, v) = ptr::read(self.raw.pair);
+            (EmptyBucket {
+                 raw: self.raw,
+                 idx: self.idx,
+                 table: self.table,
+             },
+            k,
+            v)
+        }
+    }
+}
+
+// This use of `Put` is misleading and restrictive, but safe and sufficient for our use cases
+// where `M` is a full bucket or table reference type with mutable access to the table.
+impl<K, V, M> FullBucket<K, V, M>
+    where M: Put<K, V>
+{
+    pub fn replace(&mut self, h: SafeHash, k: K, v: V) -> (SafeHash, K, V) {
+        unsafe {
+            let old_hash = ptr::replace(self.raw.hash as *mut SafeHash, h);
+            let (old_key, old_val) = ptr::replace(self.raw.pair as *mut (K, V), (k, v));
+
+            (old_hash, old_key, old_val)
+        }
+    }
+}
+
+impl<K, V, M> FullBucket<K, V, M>
+    where M: Deref<Target = RawTable<K, V>> + DerefMut
+{
+    /// Gets mutable references to the key and value at a given index.
+    pub fn read_mut(&mut self) -> (&mut K, &mut V) {
+        let pair_mut = self.raw.pair as *mut (K, V);
+        unsafe { (&mut (*pair_mut).0, &mut (*pair_mut).1) }
+    }
+}
+
+impl<'t, K, V, M> FullBucket<K, V, M>
+    where M: Deref<Target = RawTable<K, V>> + 't
+{
+    /// Exchange a bucket state for immutable references into the table.
+    /// Because the underlying reference to the table is also consumed,
+    /// no further changes to the structure of the table are possible;
+    /// in exchange for this, the returned references have a longer lifetime
+    /// than the references returned by `read()`.
+    pub fn into_refs(self) -> (&'t K, &'t V) {
+        unsafe { (&(*self.raw.pair).0, &(*self.raw.pair).1) }
+    }
+}
+
+impl<'t, K, V, M> FullBucket<K, V, M>
+    where M: Deref<Target = RawTable<K, V>> + DerefMut + 't
+{
+    /// This works similarly to `into_refs`, exchanging a bucket state
+    /// for mutable references into the table.
+    pub fn into_mut_refs(self) -> (&'t mut K, &'t mut V) {
+        let pair_mut = self.raw.pair as *mut (K, V);
+        unsafe { (&mut (*pair_mut).0, &mut (*pair_mut).1) }
+    }
+}
+
+impl<K, V, M> GapThenFull<K, V, M>
+    where M: Deref<Target = RawTable<K, V>>
+{
+    #[inline]
+    pub fn full(&self) -> &FullBucket<K, V, M> {
+        &self.full
+    }
+
+    pub fn shift(mut self) -> Option<GapThenFull<K, V, M>> {
+        unsafe {
+            *self.gap.raw.hash = mem::replace(&mut *self.full.raw.hash, EMPTY_BUCKET);
+            ptr::copy_nonoverlapping(self.full.raw.pair, self.gap.raw.pair as *mut (K, V), 1);
+        }
+
+        let FullBucket { raw: prev_raw, idx: prev_idx, .. } = self.full;
+
+        match self.full.next().peek() {
+            Full(bucket) => {
+                self.gap.raw = prev_raw;
+                self.gap.idx = prev_idx;
+
+                self.full = bucket;
+
+                Some(self)
+            }
+            Empty(..) => None,
+        }
+    }
+}
+
+
+/// Rounds up to a multiple of a power of two. Returns the closest multiple
+/// of `target_alignment` that is higher or equal to `unrounded`.
+///
+/// # Panics
+///
+/// Panics if `target_alignment` is not a power of two.
+#[inline]
+fn round_up_to_next(unrounded: usize, target_alignment: usize) -> usize {
+    assert!(target_alignment.is_power_of_two());
+    (unrounded + target_alignment - 1) & !(target_alignment - 1)
+}
+
+#[test]
+fn test_rounding() {
+    assert_eq!(round_up_to_next(0, 4), 0);
+    assert_eq!(round_up_to_next(1, 4), 4);
+    assert_eq!(round_up_to_next(2, 4), 4);
+    assert_eq!(round_up_to_next(3, 4), 4);
+    assert_eq!(round_up_to_next(4, 4), 4);
+    assert_eq!(round_up_to_next(5, 4), 8);
+}
+
+// Returns a tuple of (pairs_offset, end_of_pairs_offset),
+// from the start of a mallocated array.
+#[inline]
+fn calculate_offsets(hashes_size: usize,
+                     pairs_size: usize,
+                     pairs_align: usize)
+                     -> (usize, usize, bool) {
+    let pairs_offset = round_up_to_next(hashes_size, pairs_align);
+    let (end_of_pairs, oflo) = pairs_offset.overflowing_add(pairs_size);
+
+    (pairs_offset, end_of_pairs, oflo)
+}
+
+// Returns a tuple of (minimum required malloc alignment, hash_offset,
+// array_size), from the start of a mallocated array.
+fn calculate_allocation(hash_size: usize,
+                        hash_align: usize,
+                        pairs_size: usize,
+                        pairs_align: usize)
+                        -> (usize, usize, usize, bool) {
+    let hash_offset = 0;
+    let (_, end_of_pairs, oflo) = calculate_offsets(hash_size, pairs_size, pairs_align);
+
+    let align = cmp::max(hash_align, pairs_align);
+
+    (align, hash_offset, end_of_pairs, oflo)
+}
+
+#[test]
+fn test_offset_calculation() {
+    assert_eq!(calculate_allocation(128, 8, 16, 8), (8, 0, 144, false));
+    assert_eq!(calculate_allocation(3, 1, 2, 1), (1, 0, 5, false));
+    assert_eq!(calculate_allocation(6, 2, 12, 4), (4, 0, 20, false));
+    assert_eq!(calculate_offsets(128, 15, 4), (128, 143, false));
+    assert_eq!(calculate_offsets(3, 2, 4), (4, 6, false));
+    assert_eq!(calculate_offsets(6, 12, 4), (8, 20, false));
+}
+
+impl<K, V> RawTable<K, V> {
+    /// Does not initialize the buckets. The caller should ensure they,
+    /// at the very least, set every hash to EMPTY_BUCKET.
+    unsafe fn new_uninitialized(capacity: usize) -> RawTable<K, V> {
+        if capacity == 0 {
+            return RawTable {
+                size: 0,
+                capacity: 0,
+                hashes: Unique::new(EMPTY as *mut HashUint),
+                marker: marker::PhantomData,
+            };
+        }
+
+        // No need for `checked_mul` before a more restrictive check performed
+        // later in this method.
+        let hashes_size = capacity.wrapping_mul(size_of::<HashUint>());
+        let pairs_size = capacity.wrapping_mul(size_of::<(K, V)>());
+
+        // Allocating hashmaps is a little tricky. We need to allocate two
+        // arrays, but since we know their sizes and alignments up front,
+        // we just allocate a single array, and then have the subarrays
+        // point into it.
+        //
+        // This is great in theory, but in practice getting the alignment
+        // right is a little subtle. Therefore, calculating offsets has been
+        // factored out into a different function.
+        let (alignment, hash_offset, size, oflo) = calculate_allocation(hashes_size,
+                                                                        align_of::<HashUint>(),
+                                                                        pairs_size,
+                                                                        align_of::<(K, V)>());
+        assert!(!oflo, "capacity overflow");
+
+        // One check for overflow that covers calculation and rounding of size.
+        let size_of_bucket = size_of::<HashUint>().checked_add(size_of::<(K, V)>()).unwrap();
+        assert!(size >=
+                capacity.checked_mul(size_of_bucket)
+                    .expect("capacity overflow"),
+                "capacity overflow");
+
+        let buffer = allocate(size, alignment);
+        if buffer.is_null() {
+            ::alloc::oom()
+        }
+
+        let hashes = buffer.offset(hash_offset as isize) as *mut HashUint;
+
+        RawTable {
+            capacity: capacity,
+            size: 0,
+            hashes: Unique::new(hashes),
+            marker: marker::PhantomData,
+        }
+    }
+
+    fn first_bucket_raw(&self) -> RawBucket<K, V> {
+        let hashes_size = self.capacity * size_of::<HashUint>();
+        let pairs_size = self.capacity * size_of::<(K, V)>();
+
+        let buffer = *self.hashes as *mut u8;
+        let (pairs_offset, _, oflo) =
+            calculate_offsets(hashes_size, pairs_size, align_of::<(K, V)>());
+        debug_assert!(!oflo, "capacity overflow");
+        unsafe {
+            RawBucket {
+                hash: *self.hashes,
+                pair: buffer.offset(pairs_offset as isize) as *const _,
+                _marker: marker::PhantomData,
+            }
+        }
+    }
+
+    /// Creates a new raw table from a given capacity. All buckets are
+    /// initially empty.
+    pub fn new(capacity: usize) -> RawTable<K, V> {
+        unsafe {
+            let ret = RawTable::new_uninitialized(capacity);
+            ptr::write_bytes(*ret.hashes, 0, capacity);
+            ret
+        }
+    }
+
+    /// The hashtable's capacity, similar to a vector's.
+    pub fn capacity(&self) -> usize {
+        self.capacity
+    }
+
+    /// The number of elements ever `put` in the hashtable, minus the number
+    /// of elements ever `take`n.
+    pub fn size(&self) -> usize {
+        self.size
+    }
+
+    fn raw_buckets(&self) -> RawBuckets<K, V> {
+        RawBuckets {
+            raw: self.first_bucket_raw(),
+            hashes_end: unsafe { self.hashes.offset(self.capacity as isize) },
+            marker: marker::PhantomData,
+        }
+    }
+
+    pub fn iter(&self) -> Iter<K, V> {
+        Iter {
+            iter: self.raw_buckets(),
+            elems_left: self.size(),
+        }
+    }
+
+    pub fn iter_mut(&mut self) -> IterMut<K, V> {
+        IterMut {
+            iter: self.raw_buckets(),
+            elems_left: self.size(),
+            _marker: marker::PhantomData,
+        }
+    }
+
+    pub fn into_iter(self) -> IntoIter<K, V> {
+        let RawBuckets { raw, hashes_end, .. } = self.raw_buckets();
+        // Replace the marker regardless of lifetime bounds on parameters.
+        IntoIter {
+            iter: RawBuckets {
+                raw: raw,
+                hashes_end: hashes_end,
+                marker: marker::PhantomData,
+            },
+            table: self,
+        }
+    }
+
+    pub fn drain(&mut self) -> Drain<K, V> {
+        let RawBuckets { raw, hashes_end, .. } = self.raw_buckets();
+        // Replace the marker regardless of lifetime bounds on parameters.
+        Drain {
+            iter: RawBuckets {
+                raw: raw,
+                hashes_end: hashes_end,
+                marker: marker::PhantomData,
+            },
+            table: unsafe { Shared::new(self) },
+            marker: marker::PhantomData,
+        }
+    }
+
+    /// Returns an iterator that copies out each entry. Used while the table
+    /// is being dropped.
+    unsafe fn rev_move_buckets(&mut self) -> RevMoveBuckets<K, V> {
+        let raw_bucket = self.first_bucket_raw();
+        RevMoveBuckets {
+            raw: raw_bucket.offset(self.capacity as isize),
+            hashes_end: raw_bucket.hash,
+            elems_left: self.size,
+            marker: marker::PhantomData,
+        }
+    }
+}
+
+/// A raw iterator. The basis for some other iterators in this module. Although
+/// this interface is safe, it's not used outside this module.
+struct RawBuckets<'a, K, V> {
+    raw: RawBucket<K, V>,
+    hashes_end: *mut HashUint,
+
+    // Strictly speaking, this should be &'a (K,V), but that would
+    // require that K:'a, and we often use RawBuckets<'static...> for
+    // move iterations, so that messes up a lot of other things. So
+    // just use `&'a (K,V)` as this is not a publicly exposed type
+    // anyway.
+    marker: marker::PhantomData<&'a ()>,
+}
+
+// FIXME(#19839) Remove in favor of `#[derive(Clone)]`
+impl<'a, K, V> Clone for RawBuckets<'a, K, V> {
+    fn clone(&self) -> RawBuckets<'a, K, V> {
+        RawBuckets {
+            raw: self.raw,
+            hashes_end: self.hashes_end,
+            marker: marker::PhantomData,
+        }
+    }
+}
+
+
+impl<'a, K, V> Iterator for RawBuckets<'a, K, V> {
+    type Item = RawBucket<K, V>;
+
+    fn next(&mut self) -> Option<RawBucket<K, V>> {
+        while self.raw.hash != self.hashes_end {
+            unsafe {
+                // We are swapping out the pointer to a bucket and replacing
+                // it with the pointer to the next one.
+                let prev = ptr::replace(&mut self.raw, self.raw.offset(1));
+                if *prev.hash != EMPTY_BUCKET {
+                    return Some(prev);
+                }
+            }
+        }
+
+        None
+    }
+}
+
+/// An iterator that moves out buckets in reverse order. It leaves the table
+/// in an inconsistent state and should only be used for dropping
+/// the table's remaining entries. It's used in the implementation of Drop.
+struct RevMoveBuckets<'a, K, V> {
+    raw: RawBucket<K, V>,
+    hashes_end: *mut HashUint,
+    elems_left: usize,
+
+    // As above, `&'a (K,V)` would seem better, but we often use
+    // 'static for the lifetime, and this is not a publicly exposed
+    // type.
+    marker: marker::PhantomData<&'a ()>,
+}
+
+impl<'a, K, V> Iterator for RevMoveBuckets<'a, K, V> {
+    type Item = (K, V);
+
+    fn next(&mut self) -> Option<(K, V)> {
+        if self.elems_left == 0 {
+            return None;
+        }
+
+        loop {
+            debug_assert!(self.raw.hash != self.hashes_end);
+
+            unsafe {
+                self.raw = self.raw.offset(-1);
+
+                if *self.raw.hash != EMPTY_BUCKET {
+                    self.elems_left -= 1;
+                    return Some(ptr::read(self.raw.pair));
+                }
+            }
+        }
+    }
+}
+
+/// Iterator over shared references to entries in a table.
+pub struct Iter<'a, K: 'a, V: 'a> {
+    iter: RawBuckets<'a, K, V>,
+    elems_left: usize,
+}
+
+unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {}
+unsafe impl<'a, K: Sync, V: Sync> Send for Iter<'a, K, V> {}
+
+// FIXME(#19839) Remove in favor of `#[derive(Clone)]`
+impl<'a, K, V> Clone for Iter<'a, K, V> {
+    fn clone(&self) -> Iter<'a, K, V> {
+        Iter {
+            iter: self.iter.clone(),
+            elems_left: self.elems_left,
+        }
+    }
+}
+
+
+/// Iterator over mutable references to entries in a table.
+pub struct IterMut<'a, K: 'a, V: 'a> {
+    iter: RawBuckets<'a, K, V>,
+    elems_left: usize,
+    // To ensure invariance with respect to V
+    _marker: marker::PhantomData<&'a mut V>,
+}
+
+unsafe impl<'a, K: Sync, V: Sync> Sync for IterMut<'a, K, V> {}
+// Both K: Sync and K: Send are correct for IterMut's Send impl,
+// but Send is the more useful bound
+unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
+
+/// Iterator over the entries in a table, consuming the table.
+pub struct IntoIter<K, V> {
+    table: RawTable<K, V>,
+    iter: RawBuckets<'static, K, V>,
+}
+
+unsafe impl<K: Sync, V: Sync> Sync for IntoIter<K, V> {}
+unsafe impl<K: Send, V: Send> Send for IntoIter<K, V> {}
+
+/// Iterator over the entries in a table, clearing the table.
+pub struct Drain<'a, K: 'a, V: 'a> {
+    table: Shared<RawTable<K, V>>,
+    iter: RawBuckets<'static, K, V>,
+    marker: marker::PhantomData<&'a RawTable<K, V>>,
+}
+
+unsafe impl<'a, K: Sync, V: Sync> Sync for Drain<'a, K, V> {}
+unsafe impl<'a, K: Send, V: Send> Send for Drain<'a, K, V> {}
+
+impl<'a, K, V> Iterator for Iter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    fn next(&mut self) -> Option<(&'a K, &'a V)> {
+        self.iter.next().map(|bucket| {
+            self.elems_left -= 1;
+            unsafe { (&(*bucket.pair).0, &(*bucket.pair).1) }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.elems_left, Some(self.elems_left))
+    }
+}
+impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
+    fn len(&self) -> usize {
+        self.elems_left
+    }
+}
+
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
+        self.iter.next().map(|bucket| {
+            self.elems_left -= 1;
+            let pair_mut = bucket.pair as *mut (K, V);
+            unsafe { (&(*pair_mut).0, &mut (*pair_mut).1) }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.elems_left, Some(self.elems_left))
+    }
+}
+impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
+    fn len(&self) -> usize {
+        self.elems_left
+    }
+}
+
+impl<K, V> Iterator for IntoIter<K, V> {
+    type Item = (SafeHash, K, V);
+
+    fn next(&mut self) -> Option<(SafeHash, K, V)> {
+        self.iter.next().map(|bucket| {
+            self.table.size -= 1;
+            unsafe {
+                let (k, v) = ptr::read(bucket.pair);
+                (SafeHash { hash: *bucket.hash }, k, v)
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let size = self.table.size();
+        (size, Some(size))
+    }
+}
+impl<K, V> ExactSizeIterator for IntoIter<K, V> {
+    fn len(&self) -> usize {
+        self.table.size()
+    }
+}
+
+impl<'a, K, V> Iterator for Drain<'a, K, V> {
+    type Item = (SafeHash, K, V);
+
+    #[inline]
+    fn next(&mut self) -> Option<(SafeHash, K, V)> {
+        self.iter.next().map(|bucket| {
+            unsafe {
+                (**self.table).size -= 1;
+                let (k, v) = ptr::read(bucket.pair);
+                (SafeHash { hash: ptr::replace(bucket.hash, EMPTY_BUCKET) }, k, v)
+            }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let size = unsafe { (**self.table).size() };
+        (size, Some(size))
+    }
+}
+impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V> {
+    fn len(&self) -> usize {
+        unsafe { (**self.table).size() }
+    }
+}
+
+impl<'a, K: 'a, V: 'a> Drop for Drain<'a, K, V> {
+    fn drop(&mut self) {
+        for _ in self {}
+    }
+}
+
+impl<K: Clone, V: Clone> Clone for RawTable<K, V> {
+    fn clone(&self) -> RawTable<K, V> {
+        unsafe {
+            let mut new_ht = RawTable::new_uninitialized(self.capacity());
+
+            {
+                let cap = self.capacity();
+                let mut new_buckets = Bucket::first(&mut new_ht);
+                let mut buckets = Bucket::first(self);
+                while buckets.index() != cap {
+                    match buckets.peek() {
+                        Full(full) => {
+                            let (h, k, v) = {
+                                let (k, v) = full.read();
+                                (full.hash(), k.clone(), v.clone())
+                            };
+                            *new_buckets.raw.hash = h.inspect();
+                            ptr::write(new_buckets.raw.pair as *mut (K, V), (k, v));
+                        }
+                        Empty(..) => {
+                            *new_buckets.raw.hash = EMPTY_BUCKET;
+                        }
+                    }
+                    new_buckets.next();
+                    buckets.next();
+                }
+            };
+
+            new_ht.size = self.size();
+
+            new_ht
+        }
+    }
+}
+
+impl<K, V> Drop for RawTable<K, V> {
+    #[unsafe_destructor_blind_to_params]
+    fn drop(&mut self) {
+        if self.capacity == 0 {
+            return;
+        }
+
+        // This is done in reverse because we've likely partially taken
+        // some elements out with `.into_iter()` from the front.
+        // Check if the size is 0, so we don't do a useless scan when
+        // dropping empty tables such as on resize.
+        // Also avoid double drop of elements that have been already moved out.
+        unsafe {
+            if needs_drop::<(K, V)>() {
+                // avoid linear runtime for types that don't need drop
+                for _ in self.rev_move_buckets() {}
+            }
+        }
+
+        let hashes_size = self.capacity * size_of::<HashUint>();
+        let pairs_size = self.capacity * size_of::<(K, V)>();
+        let (align, _, size, oflo) = calculate_allocation(hashes_size,
+                                                          align_of::<HashUint>(),
+                                                          pairs_size,
+                                                          align_of::<(K, V)>());
+
+        debug_assert!(!oflo, "should be impossible");
+
+        unsafe {
+            deallocate(*self.hashes as *mut u8, size, align);
+            // Remember how everything was allocated out of one buffer
+            // during initialization? We only need one call to free here.
+        }
+    }
+}
diff --git a/ctr-std/src/collections/mod.rs b/ctr-std/src/collections/mod.rs
index 464ab25..b9e92a0 100644
--- a/ctr-std/src/collections/mod.rs
+++ b/ctr-std/src/collections/mod.rs
@@ -430,18 +430,17 @@ pub use core_collections::{binary_heap, btree_map, btree_set};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core_collections::{linked_list, vec_deque};
 
-#[cfg(feature = "not_yet_implemented")]
+#[stable(feature = "rust1", since = "1.0.0")]
 pub use self::hash_map::HashMap;
-#[cfg(feature = "not_yet_implemented")]
+#[stable(feature = "rust1", since = "1.0.0")]
 pub use self::hash_set::HashSet;
 
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core_collections::range;
 
-#[cfg(feature = "not_yet_implemented")]
 mod hash;
 
-#[cfg(feature = "not_yet_implemented")]
+#[stable(feature = "rust1", since = "1.0.0")]
 pub mod hash_map {
     //! A hash map implementation which uses linear probing with Robin
     //! Hood bucket stealing.
@@ -449,7 +448,7 @@ pub mod hash_map {
     pub use super::hash::map::*;
 }
 
-#[cfg(feature = "not_yet_implemented")]
+#[stable(feature = "rust1", since = "1.0.0")]
 pub mod hash_set {
     //! An implementation of a hash set using the underlying representation of a
     //! HashMap where the value is ().
diff --git a/ctr-std/src/lib.rs b/ctr-std/src/lib.rs
index 5b9341a..3724cc4 100644
--- a/ctr-std/src/lib.rs
+++ b/ctr-std/src/lib.rs
@@ -11,11 +11,13 @@
 #![feature(core_intrinsics)]
 #![feature(char_escape_debug)]
 #![feature(dropck_eyepatch)]
+#![feature(dropck_parametricity)]
 #![feature(float_extras)]
 #![feature(fn_traits)]
 #![feature(fnbox)]
 #![feature(fused)]
 #![feature(generic_param_attrs)]
+#![feature(heap_api)]
 #![feature(int_error_internals)]
 #![feature(integer_atomics)]
 #![feature(lang_items)]
@@ -25,7 +27,9 @@
 #![feature(optin_builtin_traits)]
 #![feature(prelude_import)]
 #![feature(raw)]
+#![feature(rand)]
 #![feature(shared)]
+#![feature(sip_hash_13)]
 #![feature(slice_concat_ext)]
 #![feature(slice_patterns)]
 #![feature(staged_api)]
@@ -54,6 +58,7 @@ extern crate core as __core;
 #[macro_reexport(vec, format)]
 extern crate collections as core_collections;
 
+#[allow(deprecated)] extern crate rand as core_rand;
 extern crate alloc;
 extern crate std_unicode;
 extern crate alloc_system;
@@ -169,12 +174,24 @@ mod sys;
 
 // Private support modules
 mod panicking;
+mod rand;
 mod memchr;
 
 // The runtime entry point and a few unstable public functions used by the
 // compiler
 pub mod rt;
 
+// Some external utilities of the standard library rely on randomness (aka
+// rustc_back::TempDir and tests) and need a way to get at the OS rng we've got
+// here. This module is not at all intended for stabilization as-is, however,
+// but it may be stabilized long-term. As a result we're exposing a hidden,
+// unstable module so we can get our build working.
+#[doc(hidden)]
+#[unstable(feature = "rand", issue = "0")]
+pub mod __rand {
+    pub use rand::{thread_rng, ThreadRng, Rng};
+}
+
 // NOTE: These two are "undefined" symbols that LLVM emits but that
 // we never actually use
 #[doc(hidden)]
diff --git a/ctr-std/src/rand/mod.rs b/ctr-std/src/rand/mod.rs
new file mode 100644
index 0000000..b853e83
--- /dev/null
+++ b/ctr-std/src/rand/mod.rs
@@ -0,0 +1,286 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Utilities for random number generation
+//!
+//! The key functions are `random()` and `Rng::gen()`. These are polymorphic
+//! and so can be used to generate any type that implements `Rand`. Type inference
+//! means that often a simple call to `rand::random()` or `rng.gen()` will
+//! suffice, but sometimes an annotation is required, e.g. `rand::random::<f64>()`.
+//!
+//! See the `distributions` submodule for sampling random numbers from
+//! distributions like normal and exponential.
+//!
+//! # Thread-local RNG
+//!
+//! There is built-in support for a RNG associated with each thread stored
+//! in thread-local storage. This RNG can be accessed via `thread_rng`, or
+//! used implicitly via `random`. This RNG is normally randomly seeded
+//! from an operating-system source of randomness, e.g. `/dev/urandom` on
+//! Unix systems, and will automatically reseed itself from this source
+//! after generating 32 KiB of random data.
+//!
+//! # Cryptographic security
+//!
+//! An application that requires an entropy source for cryptographic purposes
+//! must use `OsRng`, which reads randomness from the source that the operating
+//! system provides (e.g. `/dev/urandom` on Unixes or `CryptGenRandom()` on Windows).
+//! The other random number generators provided by this module are not suitable
+//! for such purposes.
+//!
+//! *Note*: many Unix systems provide `/dev/random` as well as `/dev/urandom`.
+//! This module uses `/dev/urandom` for the following reasons:
+//!
+//! -   On Linux, `/dev/random` may block if entropy pool is empty; `/dev/urandom` will not block.
+//!     This does not mean that `/dev/random` provides better output than
+//!     `/dev/urandom`; the kernel internally runs a cryptographically secure pseudorandom
+//!     number generator (CSPRNG) based on entropy pool for random number generation,
+//!     so the "quality" of `/dev/random` is not better than `/dev/urandom` in most cases.
+//!     However, this means that `/dev/urandom` can yield somewhat predictable randomness
+//!     if the entropy pool is very small, such as immediately after first booting.
+//!     Linux 3.17 added the `getrandom(2)` system call which solves the issue: it blocks if entropy
+//!     pool is not initialized yet, but it does not block once initialized.
+//!     `getrandom(2)` was based on `getentropy(2)`, an existing system call in OpenBSD.
+//!     `OsRng` tries to use `getrandom(2)` if available, and use `/dev/urandom` fallback if not.
+//!     If an application does not have `getrandom` and likely to be run soon after first booting,
+//!     or on a system with very few entropy sources, one should consider using `/dev/random` via
+//!     `ReaderRng`.
+//! -   On some systems (e.g. FreeBSD, OpenBSD and Mac OS X) there is no difference
+//!     between the two sources. (Also note that, on some systems e.g. FreeBSD, both `/dev/random`
+//!     and `/dev/urandom` may block once if the CSPRNG has not seeded yet.)
+
+#![unstable(feature = "rand", issue = "0")]
+
+use cell::RefCell;
+use fmt;
+use io;
+use mem;
+use rc::Rc;
+use sys;
+
+#[cfg(target_pointer_width = "32")]
+use core_rand::IsaacRng as IsaacWordRng;
+#[cfg(target_pointer_width = "64")]
+use core_rand::Isaac64Rng as IsaacWordRng;
+
+pub use core_rand::{Rand, Rng, SeedableRng};
+pub use core_rand::{XorShiftRng, IsaacRng, Isaac64Rng};
+pub use core_rand::reseeding;
+
+pub mod reader;
+
+/// The standard RNG. This is designed to be efficient on the current
+/// platform.
+#[derive(Copy, Clone)]
+pub struct StdRng {
+    rng: IsaacWordRng,
+}
+
+impl StdRng {
+    /// Create a randomly seeded instance of `StdRng`.
+    ///
+    /// This is a very expensive operation as it has to read
+    /// randomness from the operating system and use this in an
+    /// expensive seeding operation. If one is only generating a small
+    /// number of random numbers, or doesn't need the utmost speed for
+    /// generating each number, `thread_rng` and/or `random` may be more
+    /// appropriate.
+    ///
+    /// Reading the randomness from the OS may fail, and any error is
+    /// propagated via the `io::Result` return value.
+    pub fn new() -> io::Result<StdRng> {
+        OsRng::new().map(|mut r| StdRng { rng: r.gen() })
+    }
+}
+
+impl Rng for StdRng {
+    #[inline]
+    fn next_u32(&mut self) -> u32 {
+        self.rng.next_u32()
+    }
+
+    #[inline]
+    fn next_u64(&mut self) -> u64 {
+        self.rng.next_u64()
+    }
+}
+
+impl<'a> SeedableRng<&'a [usize]> for StdRng {
+    fn reseed(&mut self, seed: &'a [usize]) {
+        // the internal RNG can just be seeded from the above
+        // randomness.
+        self.rng.reseed(unsafe {mem::transmute(seed)})
+    }
+
+    fn from_seed(seed: &'a [usize]) -> StdRng {
+        StdRng { rng: SeedableRng::from_seed(unsafe {mem::transmute(seed)}) }
+    }
+}
+
+/// Controls how the thread-local RNG is reseeded.
+struct ThreadRngReseeder;
+
+impl reseeding::Reseeder<StdRng> for ThreadRngReseeder {
+    fn reseed(&mut self, rng: &mut StdRng) {
+        *rng = match StdRng::new() {
+            Ok(r) => r,
+            Err(e) => panic!("could not reseed thread_rng: {}", e)
+        }
+    }
+}
+const THREAD_RNG_RESEED_THRESHOLD: usize = 32_768;
+type ThreadRngInner = reseeding::ReseedingRng<StdRng, ThreadRngReseeder>;
+
+/// The thread-local RNG.
+#[derive(Clone)]
+pub struct ThreadRng {
+    rng: Rc<RefCell<ThreadRngInner>>,
+}
+
+impl fmt::Debug for ThreadRng {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("ThreadRng { .. }")
+    }
+}
+
+/// Retrieve the lazily-initialized thread-local random number
+/// generator, seeded by the system. Intended to be used in method
+/// chaining style, e.g. `thread_rng().gen::<isize>()`.
+///
+/// The RNG provided will reseed itself from the operating system
+/// after generating a certain amount of randomness.
+///
+/// The internal RNG used is platform and architecture dependent, even
+/// if the operating system random number generator is rigged to give
+/// the same sequence always. If absolute consistency is required,
+/// explicitly select an RNG, e.g. `IsaacRng` or `Isaac64Rng`.
+pub fn thread_rng() -> ThreadRng {
+    // used to make space in TLS for a random number generator
+    thread_local!(static THREAD_RNG_KEY: Rc<RefCell<ThreadRngInner>> = {
+        let r = match StdRng::new() {
+            Ok(r) => r,
+            Err(e) => panic!("could not initialize thread_rng: {}", e)
+        };
+        let rng = reseeding::ReseedingRng::new(r,
+                                               THREAD_RNG_RESEED_THRESHOLD,
+                                               ThreadRngReseeder);
+        Rc::new(RefCell::new(rng))
+    });
+
+    ThreadRng { rng: THREAD_RNG_KEY.with(|t| t.clone()) }
+}
+
+impl Rng for ThreadRng {
+    fn next_u32(&mut self) -> u32 {
+        self.rng.borrow_mut().next_u32()
+    }
+
+    fn next_u64(&mut self) -> u64 {
+        self.rng.borrow_mut().next_u64()
+    }
+
+    #[inline]
+    fn fill_bytes(&mut self, bytes: &mut [u8]) {
+        self.rng.borrow_mut().fill_bytes(bytes)
+    }
+}
+
+/// A random number generator that retrieves randomness straight from
+/// the operating system. Platform sources:
+///
+/// - Unix-like systems (Linux, Android, Mac OSX): read directly from
+///   `/dev/urandom`, or from `getrandom(2)` system call if available.
+/// - Windows: calls `CryptGenRandom`, using the default cryptographic
+///   service provider with the `PROV_RSA_FULL` type.
+/// - iOS: calls SecRandomCopyBytes as /dev/(u)random is sandboxed.
+/// - OpenBSD: uses the `getentropy(2)` system call.
+///
+/// This does not block.
+pub struct OsRng(sys::rand::OsRng);
+
+impl OsRng {
+    /// Create a new `OsRng`.
+    pub fn new() -> io::Result<OsRng> {
+        sys::rand::OsRng::new().map(OsRng)
+    }
+}
+
+impl Rng for OsRng {
+    #[inline]
+    fn next_u32(&mut self) -> u32 {
+        self.0.next_u32()
+    }
+
+    #[inline]
+    fn next_u64(&mut self) -> u64 {
+        self.0.next_u64()
+    }
+
+    #[inline]
+    fn fill_bytes(&mut self, bytes: &mut [u8]) {
+        self.0.fill_bytes(bytes)
+    }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use sync::mpsc::channel;
+    use rand::Rng;
+    use super::OsRng;
+    use thread;
+
+    #[test]
+    fn test_os_rng() {
+        let mut r = OsRng::new().unwrap();
+
+        r.next_u32();
+        r.next_u64();
+
+        let mut v = [0; 1000];
+        r.fill_bytes(&mut v);
+    }
+
+    #[test]
+    #[cfg_attr(target_os = "emscripten", ignore)]
+    fn test_os_rng_tasks() {
+
+        let mut txs = vec![];
+        for _ in 0..20 {
+            let (tx, rx) = channel();
+            txs.push(tx);
+
+            thread::spawn(move|| {
+                // wait until all the threads are ready to go.
+                rx.recv().unwrap();
+
+                // deschedule to attempt to interleave things as much
+                // as possible (XXX: is this a good test?)
+                let mut r = OsRng::new().unwrap();
+                thread::yield_now();
+                let mut v = [0; 1000];
+
+                for _ in 0..100 {
+                    r.next_u32();
+                    thread::yield_now();
+                    r.next_u64();
+                    thread::yield_now();
+                    r.fill_bytes(&mut v);
+                    thread::yield_now();
+                }
+            });
+        }
+
+        // start all the threads
+        for tx in &txs {
+            tx.send(()).unwrap();
+        }
+    }
+}
diff --git a/ctr-std/src/rand/reader.rs b/ctr-std/src/rand/reader.rs
new file mode 100644
index 0000000..08bc809
--- /dev/null
+++ b/ctr-std/src/rand/reader.rs
@@ -0,0 +1,108 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A wrapper around any Read to treat it as an RNG.
+
+#![allow(dead_code)]
+
+use io::prelude::*;
+use rand::Rng;
+
+/// An RNG that reads random bytes straight from a `Read`. This will
+/// work best with an infinite reader, but this is not required.
+///
+/// # Panics
+///
+/// It will panic if it there is insufficient data to fulfill a request.
+pub struct ReaderRng<R> {
+    reader: R
+}
+
+impl<R: Read> ReaderRng<R> {
+    /// Create a new `ReaderRng` from a `Read`.
+    pub fn new(r: R) -> ReaderRng<R> {
+        ReaderRng {
+            reader: r
+        }
+    }
+}
+
+impl<R: Read> Rng for ReaderRng<R> {
+    fn next_u32(&mut self) -> u32 {
+        // This is designed for speed: reading a LE integer on a LE
+        // platform just involves blitting the bytes into the memory
+        // of the u32, similarly for BE on BE; avoiding byteswapping.
+        let mut bytes = [0; 4];
+        self.fill_bytes(&mut bytes);
+        unsafe { *(bytes.as_ptr() as *const u32) }
+    }
+    fn next_u64(&mut self) -> u64 {
+        // see above for explanation.
+        let mut bytes = [0; 8];
+        self.fill_bytes(&mut bytes);
+        unsafe { *(bytes.as_ptr() as *const u64) }
+    }
+    fn fill_bytes(&mut self, mut v: &mut [u8]) {
+        while !v.is_empty() {
+            let t = v;
+            match self.reader.read(t) {
+                Ok(0) => panic!("ReaderRng.fill_bytes: EOF reached"),
+                Ok(n) => v = t.split_at_mut(n).1,
+                Err(e) => panic!("ReaderRng.fill_bytes: {}", e),
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::ReaderRng;
+    use rand::Rng;
+
+    #[test]
+    fn test_reader_rng_u64() {
+        // transmute from the target to avoid endianness concerns.
+        let v = &[0, 0, 0, 0, 0, 0, 0, 1,
+                  0, 0, 0, 0, 0, 0, 0, 2,
+                  0, 0, 0, 0, 0, 0, 0, 3][..];
+        let mut rng = ReaderRng::new(v);
+
+        assert_eq!(rng.next_u64(), 1u64.to_be());
+        assert_eq!(rng.next_u64(), 2u64.to_be());
+        assert_eq!(rng.next_u64(), 3u64.to_be());
+    }
+    #[test]
+    fn test_reader_rng_u32() {
+        let v = &[0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 3][..];
+        let mut rng = ReaderRng::new(v);
+
+        assert_eq!(rng.next_u32(), 1u32.to_be());
+        assert_eq!(rng.next_u32(), 2u32.to_be());
+        assert_eq!(rng.next_u32(), 3u32.to_be());
+    }
+    #[test]
+    fn test_reader_rng_fill_bytes() {
+        let v = [1, 2, 3, 4, 5, 6, 7, 8];
+        let mut w = [0; 8];
+
+        let mut rng = ReaderRng::new(&v[..]);
+        rng.fill_bytes(&mut w);
+
+        assert!(v == w);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_reader_rng_insufficient_bytes() {
+        let mut rng = ReaderRng::new(&[][..]);
+        let mut v = [0; 3];
+        rng.fill_bytes(&mut v);
+    }
+}
diff --git a/ctr-std/src/sys/unix/mod.rs b/ctr-std/src/sys/unix/mod.rs
index 5e44d34..4ac7a22 100644
--- a/ctr-std/src/sys/unix/mod.rs
+++ b/ctr-std/src/sys/unix/mod.rs
@@ -26,6 +26,7 @@ pub mod os_str;
 pub mod path;
 pub mod rwlock;
 pub mod thread;
+pub mod rand;
 pub mod thread_local;
 pub mod time;
 
diff --git a/ctr-std/src/sys/unix/rand.rs b/ctr-std/src/sys/unix/rand.rs
new file mode 100644
index 0000000..7fdc166
--- /dev/null
+++ b/ctr-std/src/sys/unix/rand.rs
@@ -0,0 +1,54 @@
+// Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use io::{self, Error, ErrorKind};
+use mem;
+use rand::Rng;
+
+use libctru::services::sslc::{sslcInit, sslcExit, sslcGenerateRandomData};
+
+pub struct OsRng(());
+
+impl OsRng {
+    pub fn new() -> io::Result<OsRng> {
+        unsafe { 
+            let r = sslcInit(0); 
+            if r < 0 {
+                Err(Error::new(ErrorKind::Other, "Unable to initialize the RNG"))
+            } else {
+                Ok(OsRng(()))
+            }
+        }
+    }
+}
+
+impl Rng for OsRng {
+    fn next_u32(&mut self) -> u32 {
+        let mut v = [0; 4];
+        self.fill_bytes(&mut v);
+        unsafe { mem::transmute(v) }
+    }
+
+    fn next_u64(&mut self) -> u64 {
+        let mut v = [0; 8];
+        self.fill_bytes(&mut v);
+        unsafe { mem::transmute(v) }
+    }
+
+    fn fill_bytes(&mut self, v: &mut [u8]) {
+        unsafe { sslcGenerateRandomData(v.as_ptr() as _, v.len() as u32); }
+    }
+}
+
+impl Drop for OsRng {
+    fn drop(&mut self) {
+        unsafe { sslcExit() }
+    }
+}