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libstdc++: Optimize std::string_view::find [PR 66414] 

This reuses the code from std::string::find, which was improved by
r244225, but string_view was not changed to match.

libstdc++-v3/ChangeLog:

	PR libstdc++/66414
	* include/bits/string_view.tcc
	(basic_string_view::find(const CharT*, size_type, size_type)):
	Optimize.
This commit is contained in:
Jonathan Wakely 2021-01-27 13:21:52 +00:00
parent 9d66505a5d
commit a199da782f
1 changed files with 19 additions and 7 deletions
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26
libstdc++-v3/include/bits/string_view.tcc
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@ -50,15 +50,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__glibcxx_requires_string_len(__str, __n);
if (__n == 0)
return __pos <= this->_M_len ? __pos : npos;
return __pos <= _M_len ? __pos : npos;
if (__pos >= _M_len)
return npos;
if (__n <= this->_M_len)
const _CharT __elem0 = __str[0];
const _CharT* __first = _M_str + __pos;
const _CharT* const __last = _M_str + _M_len;
size_type __len = _M_len - __pos;
while (__len >= __n)
{
for (; __pos <= this->_M_len - __n; ++__pos)
if (traits_type::eq(this->_M_str[__pos], __str[0])
&& traits_type::compare(this->_M_str + __pos + 1,
__str + 1, __n - 1) == 0)
return __pos;
// Find the first occurrence of __elem0:
__first = traits_type::find(__first, __len - __n + 1, __elem0);
if (!__first)
return npos;
// Compare the full strings from the first occurrence of __elem0.
// We already know that __first[0] == __s[0] but compare them again
// anyway because __s is probably aligned, which helps memcmp.
if (traits_type::compare(__first, __str, __n) == 0)
return __first - _M_str;
__len = __last - ++__first;
}
return npos;
}