<regex>: Revise complexity limit
#6005
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muellerj2
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<regex>: Revise complexity limit<regex>: Revise complexity limit
StephanTLavavej
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Resolves #5944.
This limits the number of state transitions by a complexity limit that grows linearly in the length of the input string. Additionally, this also takes into account the length of string comparisons in
_N_strand_N_backnodes (though divided by 64, as comparing one character is much cheaper than a single state transition).I implemented a complexity limit of
300000 + 256 * input string length. I think that should be enough for reasonable uses (and it's likely this limit will become more generous in practice when #5971 is addressed): Matching the regexa*currently performs about 3 state transitions per matched character, so 85 such loops can be tried before a complexity exception is thrown.The limit might be larger than what can fit into
_Iter_diff_t<_It>(orptrdiff_t). For this reason, two counter variables are used to implement the limit.Drive-by change: I somehow missed that
_Matcher3::_Pop_frame()is no longer in use, so this PR removes this function as well.