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Auto merge of #30917 - arthurprs:bs_bounds_check, r=alexcrichton

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Avoid bounds checking for binary search. All calculated indexes are safe and the branch is useless.
This commit is contained in:
bors 2016-01-22 19:00:15 +00:00
commit cded89a3d1
2 changed files with 15 additions and 18 deletions
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27
src/libcore/slice.rs
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@ -294,22 +294,23 @@ impl<T> SliceExt for [T] {
fn binary_search_by<F>(&self, mut f: F) -> Result<usize, usize> where
F: FnMut(&T) -> Ordering
{
let mut base : usize = 0;
let mut lim : usize = self.len();
let mut base = 0usize;
let mut s = self;
while lim != 0 {
let ix = base + (lim >> 1);
match f(&self[ix]) {
Equal => return Ok(ix),
Less => {
base = ix + 1;
lim -= 1;
}
Greater => ()
loop {
let (head, tail) = s.split_at(s.len() >> 1);
if tail.is_empty() {
return Err(base)
}
match f(&tail[0]) {
Less => {
base += head.len() + 1;
s = &tail[1..];
}
Greater => s = head,
Equal => return Ok(base + head.len()),
}
lim >>= 1;
}
Err(base)
}
#[inline]

6
src/libcoretest/slice.rs
View File

@ -11,24 +11,20 @@
use core::result::Result::{Ok, Err};
#[test]
fn binary_search_not_found() {
fn test_binary_search() {
let b = [1, 2, 4, 6, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&6)) == Ok(3));
let b = [1, 2, 4, 6, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&5)) == Err(3));
let b = [1, 2, 4, 6, 7, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&6)) == Ok(3));
let b = [1, 2, 4, 6, 7, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&5)) == Err(3));
let b = [1, 2, 4, 6, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&8)) == Ok(4));
let b = [1, 2, 4, 6, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&7)) == Err(4));
let b = [1, 2, 4, 6, 7, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&8)) == Ok(5));
let b = [1, 2, 4, 5, 6, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&7)) == Err(5));
let b = [1, 2, 4, 5, 6, 8, 9];
assert!(b.binary_search_by(|v| v.cmp(&0)) == Err(0));
let b = [1, 2, 4, 5, 6, 8];
assert!(b.binary_search_by(|v| v.cmp(&9)) == Err(6));