From 33ff7cb3386fb9477f145fa4ab74bdf70d0cb2f3 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Thu, 22 Sep 2022 18:36:04 +0100 Subject: [PATCH] libstdc++: Optimize std::bitset::to_string This makes to_string approximately twice as fast at any optimization level. Instead of iterating through every bit, jump straight to the next bit that is set, by using _Find_first and _Find_next. libstdc++-v3/ChangeLog: * include/std/bitset (bitset::_M_copy_to_string): Find set bits instead of iterating over individual bits. (cherry picked from commit ffb03fa12850df3a4f53435d5f20ff122c83732a) --- libstdc++-v3/include/std/bitset | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset index 438c2f7efe92..8ff9d7fdefdb 100644 --- a/libstdc++-v3/include/std/bitset +++ b/libstdc++-v3/include/std/bitset @@ -1415,9 +1415,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER _CharT __zero, _CharT __one) const { __s.assign(_Nb, __zero); - for (size_t __i = _Nb; __i > 0; --__i) - if (_Unchecked_test(__i - 1)) - _Traits::assign(__s[_Nb - __i], __one); + size_t __n = this->_Find_first(); + while (__n < _Nb) + { + __s[_Nb - __n - 1] = __one; + __n = _Find_next(__n); + } } // 23.3.5.3 bitset operations: -- 2.47.3