dmaax/ladybird
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

LibRegex: Use Fibonacci hashing for regex matches

Browse source 
Compared to the old boost-style combine, this reduces collisions by 36%
after folding for ranges SP=0..300, IP=0..750 and reps=0..50.
This commit is contained in:
Jelle Raaijmakers 2026-02-24 10:56:25 +01:00 committed by Jelle Raaijmakers
parent d7a8db671b
commit 04719e6491
1 changed files with 8 additions and 9 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

17
Libraries/LibRegex/RegexMatch.h
View file

@ -528,20 +528,19 @@ struct MatchState {
return flat_capture_group_matches.mutable_span().slice(match_index * capture_group_count, capture_group_count);
}
// For size_t in {0..100}, ips in {0..500} and repetitions in {0..30}, there are zero collisions.
// For the full range, zero collisions were found in 8 million random samples.
// For size_t in {0..300}, ips in {0..750} and repetitions in {0..50}, there are zero collisions.
u64 u64_hash() const
{
u64 hash = 0xcbf29ce484222325;
auto combine = [&hash](auto value) {
hash ^= value + 0x9e3779b97f4a7c15 + (hash << 6) + (hash >> 2);
hash ^= static_cast<u64>(value);
hash *= 0x9e3779b97f4a7c15;
};
auto combine_vector = [&hash](auto const& vector, auto tag) {
hash ^= tag * (vector.size() + 1);
for (auto& value : vector) {
hash ^= value;
hash *= 0x100000001b3;
}
auto combine_vector = [&combine](auto const& vector, auto tag) {
combine(tag);
combine(vector.size());
for (auto& value : vector)
combine(value);
};
combine(string_position_before_match);