diff options
Diffstat (limited to 'components/style/bloom.rs')
| -rw-r--r-- | components/style/bloom.rs | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/components/style/bloom.rs b/components/style/bloom.rs index 5033ff6ce83..34b6b608962 100644 --- a/components/style/bloom.rs +++ b/components/style/bloom.rs @@ -54,6 +54,16 @@ pub struct StyleBloom<E: TElement> { pushed_hashes: SmallVec<[u32; 64]>, } +/// The very rough benchmarks in the selectors crate show clear() +/// costing about 25 times more than remove_hash(). We use this to implement +/// clear() more efficiently when only a small number of hashes have been +/// pushed. +/// +/// One subtly to note is that remove_hash() will not touch the value +/// if the filter overflowed. However, overflow can only occur if we +/// get 255 collisions on the same hash value, and 25 < 255. +const MEMSET_CLEAR_THRESHOLD: usize = 25; + struct PushedElement<E: TElement> { /// The element that was pushed. element: SendElement<E>, @@ -166,8 +176,17 @@ impl<E: TElement> StyleBloom<E> { /// Clears the bloom filter. pub fn clear(&mut self) { - self.filter.clear(); self.elements.clear(); + + if self.pushed_hashes.len() > MEMSET_CLEAR_THRESHOLD { + self.filter.clear(); + self.pushed_hashes.clear(); + } else { + for hash in self.pushed_hashes.drain() { + self.filter.remove_hash(hash); + } + debug_assert!(self.filter.is_zeroed()); + } } /// Rebuilds the bloom filter up to the parent of the given element. |