From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2181) id 97C423858C52; Fri, 23 Sep 2022 11:58:18 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 97C423858C52 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1663934298; bh=87Tv4j1TBzOt+wzkJYAiBeQGRcITbyhMLiepvA0TOAc=; h=From:To:Subject:Date:From; b=bX2lJAN+c/3Tow4NO2Tw4TLjoL5sS7CXq3ptRCrI+WcKvN5qk8SliiKHcN+x0WuC1 hq+C5eN1ZRqYPTMMU6HqOEjonpmxdOu3BcA+2GOuWL2uKHko/m9nULyoGyL+PMw9I6 IrZFw/zbm6ADmAG1jUmL7EMt5bKHufX2lOxENMt8= MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jonathan Wakely To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r13-2814] libstdc++: Optimize std::bitset::to_string X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/master X-Git-Oldrev: 14d4b4fb12041dde1511262b926662929196c3fe X-Git-Newrev: ffb03fa12850df3a4f53435d5f20ff122c83732a Message-Id: <20220923115818.97C423858C52@sourceware.org> Date: Fri, 23 Sep 2022 11:58:18 +0000 (GMT) List-Id: https://gcc.gnu.org/g:ffb03fa12850df3a4f53435d5f20ff122c83732a commit r13-2814-gffb03fa12850df3a4f53435d5f20ff122c83732a Author: Jonathan Wakely Date: Thu Sep 22 18:36:04 2022 +0100 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. Diff: --- 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 0c84f15fda0..83c6416b770 100644 --- a/libstdc++-v3/include/std/bitset +++ b/libstdc++-v3/include/std/bitset @@ -1495,9 +1495,12 @@ _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); + } } #endif // HOSTED