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Port rust-lang/rust#78857 - Improve BinaryHeap performance #28

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Merged
merged 3 commits into from
Jan 6, 2021
Merged

Port rust-lang/rust#78857 - Improve BinaryHeap performance #28

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4dc3de1
Remove useless branches from sift_down_range loop
SkiFire13 Dec 29, 2020
e0e850f
Remove branches from sift_down_to_bottom loop
SkiFire13 Dec 29, 2020
513ce1a
Remove useless bound checks from into_sorted_vec
SkiFire13 Dec 29, 2020
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42 changes: 25 additions & 17 deletions src/binary_heap.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -938,7 +938,14 @@ impl<T, C: Compare<T>> BinaryHeap<T, C> {
let mut end = self.len();
while end > 1 {
end -= 1;
self.data.swap(0, end);
// SAFETY: `end` goes from `self.len() - 1` to 1 (both included),
// so it's always a valid index to access.
// It is safe to access index 0 (i.e. `ptr`), because
// 1 <= end < self.len(), which means self.len() >= 2.
unsafe {
let ptr = self.data.as_mut_ptr();
ptr::swap(ptr, ptr.add(end));
}
self.sift_down_range(0, end);
}
self.into_vec()
Expand Down Expand Up @@ -975,23 +982,24 @@ impl<T, C: Compare<T>> BinaryHeap<T, C> {
unsafe {
let mut hole = Hole::new(&mut self.data, pos);
let mut child = 2 * pos + 1;
while child < end {
let right = child + 1;
while child < end - 1 {
// compare with the greater of the two children
// if right < end && !(hole.get(child) > hole.get(right)) {
if right < end
&& self.cmp.compare(hole.get(child), hole.get(right)) != Ordering::Greater
{
child = right;
}
// if !(hole.get(child) > hole.get(child + 1)) { child += 1 }
child += (self.cmp.compare(hole.get(child), hole.get(child + 1))
!= Ordering::Greater) as usize;
// if we are already in order, stop.
// if hole.element() >= hole.get(child) {
if self.cmp.compare(hole.element(), hole.get(child)) != Ordering::Less {
break;
return;
}
hole.move_to(child);
child = 2 * hole.pos() + 1;
}
if child == end - 1
&& self.cmp.compare(hole.element(), hole.get(child)) == Ordering::Less
{
hole.move_to(child);
}
}
}

Expand All @@ -1011,18 +1019,18 @@ impl<T, C: Compare<T>> BinaryHeap<T, C> {
unsafe {
let mut hole = Hole::new(&mut self.data, pos);
let mut child = 2 * pos + 1;
while child < end {
while child < end - 1 {
let right = child + 1;
// compare with the greater of the two children
// if right < end && !(hole.get(child) > hole.get(right)) {
if right < end
&& self.cmp.compare(hole.get(child), hole.get(right)) != Ordering::Greater
{
child = right;
}
// if !(hole.get(child) > hole.get(right)) { child += 1 }
child += (self.cmp.compare(hole.get(child), hole.get(right)) != Ordering::Greater)
as usize;
hole.move_to(child);
child = 2 * hole.pos() + 1;
}
if child == end - 1 {
hole.move_to(child);
}
pos = hole.pos;
}
self.sift_up(start, pos);
Expand Down