C++实现高性能转换大小写算法示例

#include <string> 
#include <cctype> 
#include <algorithm>
// 字符串中的大写字符转小写
std::string strtolower(std::string s)
{
 transform(s.begin(), s.end(), s.begin(), ::tolower);
 return s;
}
// 字符串中的小写字符转大写
std::string strtoupper(std::string s)
{
 transform(s.begin(), s.end(), s.begin(), ::toupper);
 return s;
}

#include <iostream>
#include <string>
#include <stdint.h>
// 更优化
std::string strtoupper(std::string s)
{
 if(s.empty()){return s;}
 size_t len = s.size() + 1;
 size_t alignlen = len + 8 - (len % 8);
 s.resize(alignlen);
 size_t ec = alignlen / 8;
 uint64_t* p8 = (uint64_t*)s.data();
 for(size_t i=0;i<ec;++i){
 p8[i] &= 0xDFDFDFDFDFDFDFDF;
 }
 s.resize(len-1);
 return s;
}
// 未做进一步优化
std::string strtolower(std::string s)
{
 size_t len = s.size();
 size_t ec = len /8;
 uint64_t* p8 = (uint64_t*)s.data();
 for(size_t i=0;i<ec;++i){
 p8[i] |= 0x2020202020202020;
 }
 uint8_t* p1 = (uint8_t*)(p8 + ec);
 len %= 8;
 for(size_t i=0;i<len;++i){
 p1[i] |= 0x20;
 }
 return s;
}

int main()
{
 //std::cout << "Hello, world!\n";
 for(size_t i=0;i<1000000;++i){
 std::string s = strtoupper("qwertyuiopasdfghjklzxcvbnm````````QWERTYUIOPASDFGHJKLZXCVBNM");
 //std::cout<<s<<std::endl;
 s = strtolower("qwertyuiopasdfghjklzxcvbnm\t\t\t\t\t\t\t\tQWERTYUIOPASDFGHJKLZXCVBNM");
 //std::cout<<s<<std::endl;
 }
 return 0;
}

time ./teststl
./teststl 7.88s user 0.03s system 100% cpu 7.904 total

time ./test
./test 0.93s user 0.00s system 99% cpu 0.928 total