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LibRegex: Don't repeat the same fork again

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If some state has already been tried, skip over it as it would never
lead to a match regardless.
This fixes performance/memory issues in cases like
/(a+)+b/.exec("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
or
/(a|a?)+b/...

Fixes #2622.
This commit is contained in:
Ali Mohammad Pur 2025-01-15 15:22:01 +01:00 • committed by Andreas Kling
commit cce000d57c
Notes: github-actions[bot] 2025-01-17 09:35:15 +00:00
3 changed files with 66 additions and 9 deletions
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27
Libraries/LibRegex/RegexMatch.h
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@ -561,6 +561,33 @@ struct MatchState {
COWVector<Vector<Match>> capture_group_matches;
COWVector<u64> repetition_marks;
Vector<u64, 64> checkpoints;
// 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.
u64 u64_hash() const
{
u64 hash = 0xcbf29ce484222325;
auto combine = [&hash](auto value) {
hash ^= value + 0x9e3779b97f4a7c15 + (hash << 6) + (hash >> 2);
};
auto combine_vector = [&hash](auto const& vector) {
for (auto& value : vector) {
hash ^= value;
hash *= 0x100000001b3;
}
};
combine(string_position_before_match);
combine(string_position);
combine(string_position_in_code_units);
combine(instruction_position);
combine(fork_at_position);
combine(initiating_fork.value_or(0) + initiating_fork.has_value());
combine_vector(repetition_marks);
combine_vector(checkpoints);
return hash;
}
};
}