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sort: Fast path for already sorted data #29675

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Merged
merged 2 commits into from
Nov 13, 2015
Merged

sort: Fast path for already sorted data #29675

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35fd1ba
sort: Fast path for already sorted data
bluss Nov 7, 2015
0f5e30d
sort: Guard the fast path by length check
bluss Nov 7, 2015
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12 changes: 12 additions & 0 deletions src/libcollections/slice.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1066,6 +1066,18 @@ 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:
// fast-forward the left side (the right side is handled
// in the loop).
// 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);
left = right_start;
}

while out < out_end {
// Either the left or the right run are exhausted,
// so just copy the remainder from the other run
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