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sort: Guard the fast path by length check 

The right part must not be empty.
This commit is contained in:
Ulrik Sverdrup 2015-11-07 18:09:20 +01:00
parent 35fd1bab5e
commit 0f5e30d160
1 changed files with 4 additions and 2 deletions
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6
src/libcollections/slice.rs
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@ -1066,10 +1066,12 @@ fn merge_sort<T, F>(v: &mut [T], mut compare: F) where F: FnMut(&T, &T) -> Order
let mut out = buf_tmp.offset(start as isize);
let out_end = buf_tmp.offset(right_end_idx as isize);
// if left[last] <= right[0], they are already in order:
// If left[last] <= right[0], they are already in order:
// fast-forward the left side (the right side is handled
// in the loop).
if compare(&*right.offset(-1), &*right) != Greater {
// If `right` is not empty then left is not empty, and
// the offsets are in bounds.
if right != right_end && compare(&*right.offset(-1), &*right) != Greater {
let elems = (right_start as usize - left as usize) / mem::size_of::<T>();
ptr::copy_nonoverlapping(&*left, out, elems);
out = out.offset(elems as isize);