add libcore from 2016-04-11 nightly

1 files changed, 94 insertions, 0 deletions

diff --git a/libcore/num/dec2flt/num.rs b/libcore/num/dec2flt/num.rs
new file mode 100644
index 0000000..81e7856
--- /dev/null
+++ b/libcore/num/dec2flt/num.rs
@@ -0,0 +1,94 @@
+// Copyright 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.
+
+//! Utility functions for bignums that don't make too much sense to turn into methods.
+
+// FIXME This module's name is a bit unfortunate, since other modules also import `core::num`.
+
+use prelude::v1::*;
+use cmp::Ordering::{self, Less, Equal, Greater};
+
+pub use num::bignum::Big32x40 as Big;
+
+/// Test whether truncating all bits less significant than `ones_place` introduces
+/// a relative error less, equal, or greater than 0.5 ULP.
+pub fn compare_with_half_ulp(f: &Big, ones_place: usize) -> Ordering {
+    if ones_place == 0 {
+        return Less;
+    }
+    let half_bit = ones_place - 1;
+    if f.get_bit(half_bit) == 0 {
+        // < 0.5 ULP
+        return Less;
+    }
+    // If all remaining bits are zero, it's = 0.5 ULP, otherwise > 0.5
+    // If there are no more bits (half_bit == 0), the below also correctly returns Equal.
+    for i in 0..half_bit {
+        if f.get_bit(i) == 1 {
+            return Greater;
+        }
+    }
+    Equal
+}
+
+/// Convert an ASCII string containing only decimal digits to a `u64`.
+///
+/// Does not perform checks for overflow or invalid characters, so if the caller is not careful,
+/// the result is bogus and can panic (though it won't be `unsafe`). Additionally, empty strings
+/// are treated as zero. This function exists because
+///
+/// 1. using `FromStr` on `&[u8]` requires `from_utf8_unchecked`, which is bad, and
+/// 2. piecing together the results of `integral.parse()` and `fractional.parse()` is
+///    more complicated than this entire function.
+pub fn from_str_unchecked<'a, T>(bytes: T) -> u64 where T : IntoIterator<Item=&'a u8> {
+    let mut result = 0;
+    for &c in bytes {
+        result = result * 10 + (c - b'0') as u64;
+    }
+    result
+}
+
+/// Convert a string of ASCII digits into a bignum.
+///
+/// Like `from_str_unchecked`, this function relies on the parser to weed out non-digits.
+pub fn digits_to_big(integral: &[u8], fractional: &[u8]) -> Big {
+    let mut f = Big::from_small(0);
+    for &c in integral.iter().chain(fractional) {
+        let n = (c - b'0') as u32;
+        f.mul_small(10);
+        f.add_small(n);
+    }
+    f
+}
+
+/// Unwraps a bignum into a 64 bit integer. Panics if the number is too large.
+pub fn to_u64(x: &Big) -> u64 {
+    assert!(x.bit_length() < 64);
+    let d = x.digits();
+    if d.len() < 2 {
+        d[0] as u64
+    } else {
+        (d[1] as u64) << 32 | d[0] as u64
+    }
+}
+
+
+/// Extract a range of bits.
+
+/// Index 0 is the least significant bit and the range is half-open as usual.
+/// Panics if asked to extract more bits than fit into the return type.
+pub fn get_bits(x: &Big, start: usize, end: usize) -> u64 {
+    assert!(end - start <= 64);
+    let mut result: u64 = 0;
+    for i in (start..end).rev() {
+        result = result << 1 | x.get_bit(i) as u64;
+    }
+    result
+}