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<regex>: Fix quadratic complexity in regex_search when regex starts with ? quantifier or several alternatives #5457

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Merged
merged 2 commits into from
May 10, 2025
Merged

<regex>: Fix quadratic complexity in regex_search when regex starts with ? quantifier or several alternatives #5457

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3639e62
`<regex>`: Fix quadratic complexity in `regex_search` when regex star…
muellerj2 May 1, 2025
776a8ee
remove nullptr
muellerj2 May 1, 2025
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15 changes: 7 additions & 8 deletions stl/inc/regex
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Original file line number Diff line number Diff line change
Expand Up @@ -3931,23 +3931,22 @@ _BidIt _Matcher<_BidIt, _Elem, _RxTraits, _It>::_Skip(_BidIt _First_arg, _BidIt
break;

case _N_if:
{ // check for soonest string match
{
// GH-5452: If this node has two or more branches,
// examining all these branches has quadratic worst-case complexity.
// Thus, we only continue if this node has a single branch only.
_Node_if* _Node = static_cast<_Node_if*>(_Nx);

for (; _First_arg != _Last && _Node; _Node = _Node->_Child) {
_Last = _Skip(_First_arg, _Last, _Node->_Next);
if (_Node->_Child != nullptr) {
return _First_arg;
}

return _Last;
break;
}

case _N_begin:
break;

case _N_end:
_Nx = nullptr;
break;

case _N_none:
case _N_wbound:
case _N_dot:
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