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Speedup heapsort by 1.8x by making it branchless #107894

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merged 2 commits into from
Feb 12, 2023
Merged

Speedup heapsort by 1.8x by making it branchless #107894

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7e07219
Speedup heapsort by 1.5x by making it branchless
Voultapher Feb 10, 2023
ee0376c
Split branches in heapsort child selection
Voultapher Feb 11, 2023
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7 changes: 5 additions & 2 deletions library/core/src/slice/sort.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -198,8 +198,11 @@ where
}

// Choose the greater child.
if child + 1 < v.len() && is_less(&v[child], &v[child + 1]) {
child += 1;
if child + 1 < v.len() {
// We need a branch to be sure not to out-of-bounds index,
// but it's highly predictable. The comparison, however,
// is better done branchless, especially for primitives.
child += is_less(&v[child], &v[child + 1]) as usize;
}

// Stop if the invariant holds at `node`.
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