From 2c816f7fb6772fe0b77af04da9355aab6c2d3fb2 Mon Sep 17 00:00:00 2001 From: Stjepan Glavina Date: Sat, 25 Mar 2017 00:27:47 +0100 Subject: [PATCH] Optimize insertion sort This change slightly changes the main iteration loop so that LLVM can optimize it more efficiently. Benchmark: name before ns/iter after ns/iter diff ns/iter diff % slice::sort_unstable_small_ascending 39 (2051 MB/s) 38 (2105 MB/s) -1 -2.56% slice::sort_unstable_small_big_random 579 (2210 MB/s) 575 (2226 MB/s) -4 -0.69% slice::sort_unstable_small_descending 80 (1000 MB/s) 70 (1142 MB/s) -10 -12.50% slice::sort_unstable_small_random 396 (202 MB/s) 386 -10 -2.53% --- src/libcore/slice/sort.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/libcore/slice/sort.rs b/src/libcore/slice/sort.rs index d13d537d99301..307e4974d9769 100644 --- a/src/libcore/slice/sort.rs +++ b/src/libcore/slice/sort.rs @@ -152,8 +152,8 @@ fn partial_insertion_sort(v: &mut [T], is_less: &mut F) -> bool fn insertion_sort(v: &mut [T], is_less: &mut F) where F: FnMut(&T, &T) -> bool { - for i in 2..v.len()+1 { - shift_tail(&mut v[..i], is_less); + for i in 1..v.len() { + shift_tail(&mut v[..i+1], is_less); } }