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Change rebuild heuristic in BinaryHeap::append

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See #77433 for why the new heuristic was chosen.

Fixes #77433
This commit is contained in:
Han Mertens 2021-01-15 21:50:05 +01:00
parent e48eb37b94
commit 32a20f4433
1 changed files with 8 additions and 2 deletions
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10
library/alloc/src/collections/binary_heap.rs
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@ -630,10 +630,16 @@ impl<T: Ord> BinaryHeap<T> {
// and about 2 * (len1 + len2) comparisons in the worst case // and about 2 * (len1 + len2) comparisons in the worst case
// while `extend` takes O(len2 * log(len1)) operations // while `extend` takes O(len2 * log(len1)) operations
// and about 1 * len2 * log_2(len1) comparisons in the worst case, // and about 1 * len2 * log_2(len1) comparisons in the worst case,
// assuming len1 >= len2. // assuming len1 >= len2. For larger heaps, the crossover point
// no longer follows this reasoning and was determined empirically.
#[inline] #[inline]
fn better_to_rebuild(len1: usize, len2: usize) -> bool { fn better_to_rebuild(len1: usize, len2: usize) -> bool {
2 * (len1 + len2) < len2 * log2_fast(len1) let tot_len = len1 + len2;
if tot_len <= 2048 {
2 * tot_len < len2 * log2_fast(len1)
} else {
2 * tot_len < len2 * 11
}
} }
if better_to_rebuild(self.len(), other.len()) { if better_to_rebuild(self.len(), other.len()) {