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Make backstep calculation non-recursive.

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Refs https://github.com/boostorg/regex/pull/236.
This commit is contained in:
jzmaddock
2024-12-16 16:58:25 +00:00
parent 0cbaa4ef17
commit 57ca08240e
3 changed files with 62 additions and 6 deletions
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38
include/boost/regex/v5/basic_regex_creator.hpp
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@ -974,7 +974,12 @@ template <class charT, class traits>
int basic_regex_creator<charT, traits>::calculate_backstep(re_syntax_base* state)
{
typedef typename traits::char_class_type m_type;
int result = 0;
int last_alternative_result = -1;
std::vector<std::tuple<int, re_syntax_base*>> stack;
while(state)
{
switch(state->type)
@ -993,9 +998,28 @@ int basic_regex_creator<charT, traits>::calculate_backstep(re_syntax_base* state
}
break;
case syntax_element_endmark:
if((static_cast<re_brace*>(state)->index == -1)
if ((static_cast<re_brace*>(state)->index == -1)
|| (static_cast<re_brace*>(state)->index == -2))
return result;
{
// We've finished the calculation, check against any previous alternatives:
if (last_alternative_result >= 0)
{
if (last_alternative_result != result)
return -1;
}
else
last_alternative_result = result;
if (stack.size())
{
// Skip to next alternative and calculate that as well:
std::tie(result, state) = stack.back();
stack.pop_back();
continue;
}
else
return result;
}
break;
case syntax_element_literal:
result += static_cast<re_literal*>(state)->length;
@ -1051,11 +1075,13 @@ int basic_regex_creator<charT, traits>::calculate_backstep(re_syntax_base* state
continue;
case syntax_element_alt:
{
int r1 = calculate_backstep(state->next.p);
int r2 = calculate_backstep(static_cast<re_alt*>(state)->alt.p);
if((r1 < 0) || (r1 != r2))
// Push the alternative if we haven't pushed too many already:
if(stack.size() > BOOST_REGEX_MAX_BLOCKS)
return -1;
return result + r1;
stack.push_back(std::make_tuple(result, static_cast<re_alt*>(state)->alt.p));
// and take the first one:
state = state->next.p;
continue;
}
default:
break;