add libcore from 2016-04-11 nightly

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+// Copyright 2012-2014 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.
+
+//! Basic functions for dealing with memory.
+//!
+//! This module contains functions for querying the size and alignment of
+//! types, initializing and manipulating memory.
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use marker::Sized;
+use intrinsics;
+use ptr;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use intrinsics::transmute;
+
+/// Leaks a value into the void, consuming ownership and never running its
+/// destructor.
+///
+/// This function will take ownership of its argument, but is distinct from the
+/// `mem::drop` function in that it **does not run the destructor**, leaking the
+/// value and any resources that it owns.
+///
+/// There's only a few reasons to use this function. They mainly come
+/// up in unsafe code or FFI code.
+///
+/// * You have an uninitialized value, perhaps for performance reasons, and
+///   need to prevent the destructor from running on it.
+/// * You have two copies of a value (like when writing something like
+///   [`mem::swap`][swap]), but need the destructor to only run once to
+///   prevent a double `free`.
+/// * Transferring resources across [FFI][ffi] boundaries.
+///
+/// [swap]: fn.swap.html
+/// [ffi]: ../../book/ffi.html
+///
+/// # Safety
+///
+/// This function is not marked as `unsafe` as Rust does not guarantee that the
+/// `Drop` implementation for a value will always run. Note, however, that
+/// leaking resources such as memory or I/O objects is likely not desired, so
+/// this function is only recommended for specialized use cases.
+///
+/// The safety of this function implies that when writing `unsafe` code
+/// yourself care must be taken when leveraging a destructor that is required to
+/// run to preserve memory safety. There are known situations where the
+/// destructor may not run (such as if ownership of the object with the
+/// destructor is returned) which must be taken into account.
+///
+/// # Other forms of Leakage
+///
+/// It's important to point out that this function is not the only method by
+/// which a value can be leaked in safe Rust code. Other known sources of
+/// leakage are:
+///
+/// * `Rc` and `Arc` cycles
+/// * `mpsc::{Sender, Receiver}` cycles (they use `Arc` internally)
+/// * Panicking destructors are likely to leak local resources
+///
+/// # Example
+///
+/// Leak some heap memory by never deallocating it:
+///
+/// ```rust
+/// use std::mem;
+///
+/// let heap_memory = Box::new(3);
+/// mem::forget(heap_memory);
+/// ```
+///
+/// Leak an I/O object, never closing the file:
+///
+/// ```rust,no_run
+/// use std::mem;
+/// use std::fs::File;
+///
+/// let file = File::open("foo.txt").unwrap();
+/// mem::forget(file);
+/// ```
+///
+/// The `mem::swap` function uses `mem::forget` to good effect:
+///
+/// ```rust
+/// use std::mem;
+/// use std::ptr;
+///
+/// # #[allow(dead_code)]
+/// fn swap<T>(x: &mut T, y: &mut T) {
+///     unsafe {
+///         // Give ourselves some scratch space to work with
+///         let mut t: T = mem::uninitialized();
+///
+///         // Perform the swap, `&mut` pointers never alias
+///         ptr::copy_nonoverlapping(&*x, &mut t, 1);
+///         ptr::copy_nonoverlapping(&*y, x, 1);
+///         ptr::copy_nonoverlapping(&t, y, 1);
+///
+///         // y and t now point to the same thing, but we need to completely
+///         // forget `t` because we do not want to run the destructor for `T`
+///         // on its value, which is still owned somewhere outside this function.
+///         mem::forget(t);
+///     }
+/// }
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn forget<T>(t: T) {
+    unsafe { intrinsics::forget(t) }
+}
+
+/// Returns the size of a type in bytes.
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// assert_eq!(4, mem::size_of::<i32>());
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn size_of<T>() -> usize {
+    unsafe { intrinsics::size_of::<T>() }
+}
+
+/// Returns the size of the given value in bytes.
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// assert_eq!(4, mem::size_of_val(&5i32));
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
+    unsafe { intrinsics::size_of_val(val) }
+}
+
+/// Returns the ABI-required minimum alignment of a type
+///
+/// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
+///
+/// # Examples
+///
+/// ```
+/// # #![allow(deprecated)]
+/// use std::mem;
+///
+/// assert_eq!(4, mem::min_align_of::<i32>());
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_deprecated(reason = "use `align_of` instead", since = "1.2.0")]
+pub fn min_align_of<T>() -> usize {
+    unsafe { intrinsics::min_align_of::<T>() }
+}
+
+/// Returns the ABI-required minimum alignment of the type of the value that `val` points to
+///
+/// # Examples
+///
+/// ```
+/// # #![allow(deprecated)]
+/// use std::mem;
+///
+/// assert_eq!(4, mem::min_align_of_val(&5i32));
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_deprecated(reason = "use `align_of_val` instead", since = "1.2.0")]
+pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
+    unsafe { intrinsics::min_align_of_val(val) }
+}
+
+/// Returns the alignment in memory for a type.
+///
+/// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// assert_eq!(4, mem::align_of::<i32>());
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn align_of<T>() -> usize {
+    unsafe { intrinsics::min_align_of::<T>() }
+}
+
+/// Returns the ABI-required minimum alignment of the type of the value that `val` points to
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// assert_eq!(4, mem::align_of_val(&5i32));
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
+    unsafe { intrinsics::min_align_of_val(val) }
+}
+
+/// Creates a value initialized to zero.
+///
+/// This function is similar to allocating space for a local variable and zeroing it out (an unsafe
+/// operation).
+///
+/// Care must be taken when using this function, if the type `T` has a destructor and the value
+/// falls out of scope (due to unwinding or returning) before being initialized, then the
+/// destructor will run on zeroed data, likely leading to crashes.
+///
+/// This is useful for FFI functions sometimes, but should generally be avoided.
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// let x: i32 = unsafe { mem::zeroed() };
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub unsafe fn zeroed<T>() -> T {
+    intrinsics::init()
+}
+
+/// Creates a value initialized to an unspecified series of bytes.
+///
+/// The byte sequence usually indicates that the value at the memory
+/// in question has been dropped. Thus, *if* T carries a drop flag,
+/// any associated destructor will not be run when the value falls out
+/// of scope.
+///
+/// Some code at one time used the `zeroed` function above to
+/// accomplish this goal.
+///
+/// This function is expected to be deprecated with the transition
+/// to non-zeroing drop.
+#[inline]
+#[unstable(feature = "filling_drop", issue = "5016")]
+pub unsafe fn dropped<T>() -> T {
+    #[inline(always)]
+    unsafe fn dropped_impl<T>() -> T { intrinsics::init_dropped() }
+
+    dropped_impl()
+}
+
+/// Bypasses Rust's normal memory-initialization checks by pretending to
+/// produce a value of type T, while doing nothing at all.
+///
+/// **This is incredibly dangerous, and should not be done lightly. Deeply
+/// consider initializing your memory with a default value instead.**
+///
+/// This is useful for FFI functions and initializing arrays sometimes,
+/// but should generally be avoided.
+///
+/// # Undefined Behavior
+///
+/// It is Undefined Behavior to read uninitialized memory. Even just an
+/// uninitialized boolean. For instance, if you branch on the value of such
+/// a boolean your program may take one, both, or neither of the branches.
+///
+/// Note that this often also includes *writing* to the uninitialized value.
+/// Rust believes the value is initialized, and will therefore try to Drop
+/// the uninitialized value and its fields if you try to overwrite the memory
+/// in a normal manner. The only way to safely initialize an arbitrary
+/// uninitialized value is with one of the `ptr` functions: `write`, `copy`, or
+/// `copy_nonoverlapping`. This isn't necessary if `T` is a primitive
+/// or otherwise only contains types that don't implement Drop.
+///
+/// If this value *does* need some kind of Drop, it must be initialized before
+/// it goes out of scope (and therefore would be dropped). Note that this
+/// includes a `panic` occurring and unwinding the stack suddenly.
+///
+/// # Examples
+///
+/// Here's how to safely initialize an array of `Vec`s.
+///
+/// ```
+/// use std::mem;
+/// use std::ptr;
+///
+/// // Only declare the array. This safely leaves it
+/// // uninitialized in a way that Rust will track for us.
+/// // However we can't initialize it element-by-element
+/// // safely, and we can't use the `[value; 1000]`
+/// // constructor because it only works with `Copy` data.
+/// let mut data: [Vec<u32>; 1000];
+///
+/// unsafe {
+///     // So we need to do this to initialize it.
+///     data = mem::uninitialized();
+///
+///     // DANGER ZONE: if anything panics or otherwise
+///     // incorrectly reads the array here, we will have
+///     // Undefined Behavior.
+///
+///     // It's ok to mutably iterate the data, since this
+///     // doesn't involve reading it at all.
+///     // (ptr and len are statically known for arrays)
+///     for elem in &mut data[..] {
+///         // *elem = Vec::new() would try to drop the
+///         // uninitialized memory at `elem` -- bad!
+///         //
+///         // Vec::new doesn't allocate or do really
+///         // anything. It's only safe to call here
+///         // because we know it won't panic.
+///         ptr::write(elem, Vec::new());
+///     }
+///
+///     // SAFE ZONE: everything is initialized.
+/// }
+///
+/// println!("{:?}", &data[0]);
+/// ```
+///
+/// This example emphasizes exactly how delicate and dangerous doing this is.
+/// Note that the `vec!` macro *does* let you initialize every element with a
+/// value that is only `Clone`, so the following is semantically equivalent and
+/// vastly less dangerous, as long as you can live with an extra heap
+/// allocation:
+///
+/// ```
+/// let data: Vec<Vec<u32>> = vec![Vec::new(); 1000];
+/// println!("{:?}", &data[0]);
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub unsafe fn uninitialized<T>() -> T {
+    intrinsics::uninit()
+}
+
+/// Swap the values at two mutable locations of the same type, without deinitializing or copying
+/// either one.
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// let x = &mut 5;
+/// let y = &mut 42;
+///
+/// mem::swap(x, y);
+///
+/// assert_eq!(42, *x);
+/// assert_eq!(5, *y);
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn swap<T>(x: &mut T, y: &mut T) {
+    unsafe {
+        // Give ourselves some scratch space to work with
+        let mut t: T = uninitialized();
+
+        // Perform the swap, `&mut` pointers never alias
+        ptr::copy_nonoverlapping(&*x, &mut t, 1);
+        ptr::copy_nonoverlapping(&*y, x, 1);
+        ptr::copy_nonoverlapping(&t, y, 1);
+
+        // y and t now point to the same thing, but we need to completely
+        // forget `t` because we do not want to run the destructor for `T`
+        // on its value, which is still owned somewhere outside this function.
+        forget(t);
+    }
+}
+
+/// Replaces the value at a mutable location with a new one, returning the old value, without
+/// deinitializing or copying either one.
+///
+/// This is primarily used for transferring and swapping ownership of a value in a mutable
+/// location.
+///
+/// # Examples
+///
+/// A simple example:
+///
+/// ```
+/// use std::mem;
+///
+/// let mut v: Vec<i32> = Vec::new();
+///
+/// mem::replace(&mut v, Vec::new());
+/// ```
+///
+/// This function allows consumption of one field of a struct by replacing it with another value.
+/// The normal approach doesn't always work:
+///
+/// ```rust,ignore
+/// struct Buffer<T> { buf: Vec<T> }
+///
+/// impl<T> Buffer<T> {
+///     fn get_and_reset(&mut self) -> Vec<T> {
+///         // error: cannot move out of dereference of `&mut`-pointer
+///         let buf = self.buf;
+///         self.buf = Vec::new();
+///         buf
+///     }
+/// }
+/// ```
+///
+/// Note that `T` does not necessarily implement `Clone`, so it can't even clone and reset
+/// `self.buf`. But `replace` can be used to disassociate the original value of `self.buf` from
+/// `self`, allowing it to be returned:
+///
+/// ```
+/// # #![allow(dead_code)]
+/// use std::mem;
+/// # struct Buffer<T> { buf: Vec<T> }
+/// impl<T> Buffer<T> {
+///     fn get_and_reset(&mut self) -> Vec<T> {
+///         mem::replace(&mut self.buf, Vec::new())
+///     }
+/// }
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn replace<T>(dest: &mut T, mut src: T) -> T {
+    swap(dest, &mut src);
+    src
+}
+
+/// Disposes of a value.
+///
+/// While this does call the argument's implementation of `Drop`, it will not
+/// release any borrows, as borrows are based on lexical scope.
+///
+/// This effectively does nothing for
+/// [types which implement `Copy`](../../book/ownership.html#copy-types),
+/// e.g. integers. Such values are copied and _then_ moved into the function,
+/// so the value persists after this function call.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// let v = vec![1, 2, 3];
+///
+/// drop(v); // explicitly drop the vector
+/// ```
+///
+/// Borrows are based on lexical scope, so this produces an error:
+///
+/// ```ignore
+/// let mut v = vec![1, 2, 3];
+/// let x = &v[0];
+///
+/// drop(x); // explicitly drop the reference, but the borrow still exists
+///
+/// v.push(4); // error: cannot borrow `v` as mutable because it is also
+///            // borrowed as immutable
+/// ```
+///
+/// An inner scope is needed to fix this:
+///
+/// ```
+/// let mut v = vec![1, 2, 3];
+///
+/// {
+///     let x = &v[0];
+///
+///     drop(x); // this is now redundant, as `x` is going out of scope anyway
+/// }
+///
+/// v.push(4); // no problems
+/// ```
+///
+/// Since `RefCell` enforces the borrow rules at runtime, `drop()` can
+/// seemingly release a borrow of one:
+///
+/// ```
+/// use std::cell::RefCell;
+///
+/// let x = RefCell::new(1);
+///
+/// let mut mutable_borrow = x.borrow_mut();
+/// *mutable_borrow = 1;
+///
+/// drop(mutable_borrow); // relinquish the mutable borrow on this slot
+///
+/// let borrow = x.borrow();
+/// println!("{}", *borrow);
+/// ```
+///
+/// Integers and other types implementing `Copy` are unaffected by `drop()`
+///
+/// ```
+/// #[derive(Copy, Clone)]
+/// struct Foo(u8);
+///
+/// let x = 1;
+/// let y = Foo(2);
+/// drop(x); // a copy of `x` is moved and dropped
+/// drop(y); // a copy of `y` is moved and dropped
+///
+/// println!("x: {}, y: {}", x, y.0); // still available
+/// ```
+///
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn drop<T>(_x: T) { }
+
+macro_rules! repeat_u8_as_u32 {
+    ($name:expr) => { (($name as u32) << 24 |
+                       ($name as u32) << 16 |
+                       ($name as u32) <<  8 |
+                       ($name as u32)) }
+}
+macro_rules! repeat_u8_as_u64 {
+    ($name:expr) => { ((repeat_u8_as_u32!($name) as u64) << 32 |
+                       (repeat_u8_as_u32!($name) as u64)) }
+}
+
+// NOTE: Keep synchronized with values used in librustc_trans::trans::adt.
+//
+// In particular, the POST_DROP_U8 marker must never equal the
+// DTOR_NEEDED_U8 marker.
+//
+// For a while pnkfelix was using 0xc1 here.
+// But having the sign bit set is a pain, so 0x1d is probably better.
+//
+// And of course, 0x00 brings back the old world of zero'ing on drop.
+#[unstable(feature = "filling_drop", issue = "5016")]
+#[allow(missing_docs)]
+pub const POST_DROP_U8: u8 = 0x1d;
+#[unstable(feature = "filling_drop", issue = "5016")]
+#[allow(missing_docs)]
+pub const POST_DROP_U32: u32 = repeat_u8_as_u32!(POST_DROP_U8);
+#[unstable(feature = "filling_drop", issue = "5016")]
+#[allow(missing_docs)]
+pub const POST_DROP_U64: u64 = repeat_u8_as_u64!(POST_DROP_U8);
+
+#[cfg(target_pointer_width = "32")]
+#[unstable(feature = "filling_drop", issue = "5016")]
+#[allow(missing_docs)]
+pub const POST_DROP_USIZE: usize = POST_DROP_U32 as usize;
+#[cfg(target_pointer_width = "64")]
+#[unstable(feature = "filling_drop", issue = "5016")]
+#[allow(missing_docs)]
+pub const POST_DROP_USIZE: usize = POST_DROP_U64 as usize;
+
+/// Interprets `src` as `&U`, and then reads `src` without moving the contained
+/// value.
+///
+/// This function will unsafely assume the pointer `src` is valid for
+/// `sizeof(U)` bytes by transmuting `&T` to `&U` and then reading the `&U`. It
+/// will also unsafely create a copy of the contained value instead of moving
+/// out of `src`.
+///
+/// It is not a compile-time error if `T` and `U` have different sizes, but it
+/// is highly encouraged to only invoke this function where `T` and `U` have the
+/// same size. This function triggers undefined behavior if `U` is larger than
+/// `T`.
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// #[repr(packed)]
+/// struct Foo {
+///     bar: u8,
+/// }
+///
+/// let foo_slice = [10u8];
+///
+/// unsafe {
+///     // Copy the data from 'foo_slice' and treat it as a 'Foo'
+///     let mut foo_struct: Foo = mem::transmute_copy(&foo_slice);
+///     assert_eq!(foo_struct.bar, 10);
+///
+///     // Modify the copied data
+///     foo_struct.bar = 20;
+///     assert_eq!(foo_struct.bar, 20);
+/// }
+///
+/// // The contents of 'foo_slice' should not have changed
+/// assert_eq!(foo_slice, [10]);
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub unsafe fn transmute_copy<T, U>(src: &T) -> U {
+    ptr::read(src as *const T as *const U)
+}