string.h的strcmp的性能比较

string.h基于汇编实现strcmp ,和普通strcmp，针对循环调用次数和字符串查找长度2个纬度做了一次性能对比效测试。

#include <sys/socket.h>#include <sys/epoll.h>#include <netinet/in.h>#include <arpa/inet.h>#include <fcntl.h>#include <unistd.h>#include <stdio.h>#include <errno.h>#include <iostream>#include <strings.h>#include <string.h>#include <stdlib.h>#include <sys/time.h>using namespace std;static inline int strcmp_asm(const char * cs,const char * ct){    int d0, d1;    register int __res;    __asm__ __volatile__(            "1:\tlodsb\n\t"            "scasb\n\t"            "jne 2f\n\t"            "testb %%al,%%al\n\t"            "jne 1b\n\t"            "xorl %%eax,%%eax\n\t"            "jmp 3f\n"            "2:\tsbbl %%eax,%%eax\n\t"            "orb $1,%%al\n"            "3:"            :"=a" (__res), "=&S" (d0), "=&D" (d1)            :"1" (cs),"2" (ct));    return __res;}static inline int strcmp_normal(const char * cs,const char * ct){    while(*cs!='\0' && *ct!='\0')    {        if(*cs != *ct)            return *cs<*ct?-1:1;        cs++;        ct++;    }    if(*cs != *ct)        return *cs<*ct?-1:1;    return 0;}static inline int generator_data(string &s,int iSamelen=1,const char *sepc=NULL){    s.clear();    for(int i=0;i<iSamelen;++i)        s+="1";    s+=sepc;    return 0;}static inline void strcmp_perfom(int loop=1,int iSamelen=1){    //loop asm    string s1,s2;    generator_data(s1,iSamelen,"s1");    generator_data(s2,iSamelen,"s2");    struct timeval start_tv,loop1_tv;    gettimeofday(&start_tv, NULL);    for(int i=0;i<loop;++i)    {        strcmp_asm(s1.c_str(),s2.c_str());    }    gettimeofday(&loop1_tv, NULL);    int iMs = (loop1_tv.tv_sec - start_tv.tv_sec)*1000 + (loop1_tv.tv_usec - start_tv.tv_usec)/1000;    //loop normal    string ss1,ss2;    generator_data(ss1,iSamelen,"s1");    generator_data(ss2,iSamelen,"s2");    gettimeofday(&start_tv, NULL);    for(int i=0;i<loop;++i)    {        strcmp_normal(ss1.c_str(),ss2.c_str());    }    gettimeofday(&loop1_tv, NULL);    int iMs2 = (loop1_tv.tv_sec - start_tv.tv_sec)*1000 + (loop1_tv.tv_usec - start_tv.tv_usec)/1000;    printf("loop:%d,strcmp_asm,time:%d ms,strcmp_normal,time:%d ms\n",loop,iMs,iMs2);}int main(int argc,char** argv){    int loop=10000;    int iSamelen=1000;    if(argc>1)    {        loop = atoll(argv[1]);    }    if(argc>2)    {        iSamelen = atoll(argv[2]);    }    printf("input loop:%d,iSamelen:%d\n",loop,iSamelen);    strcmp_perfom(loop,iSamelen);    return 0;}

测试结果如下，在匹配串长度足够的情况下，性能差了3~4倍。
input loop:5000,iSamelen:100000
loop:5000,strcmp_asm,time:468 ms,strcmp_normal,time:1747 ms


input loop:50000,iSamelen:10000
loop:50000,strcmp_asm,time:501 ms,strcmp_normal,time:1749 ms


input loop:500000,iSamelen:1000
loop:500000,strcmp_asm,time:494 ms,strcmp_normal,time:1787 ms


input loop:5000000,iSamelen:100
loop:5000000,strcmp_asm,time:693 ms,strcmp_normal,time:1922 ms


input loop:50000000,iSamelen:10
loop:50000000,strcmp_asm,time:1337 ms,strcmp_normal,time:2424 ms


在匹配串极短的场景，1，2，4字节的情况，性能也有1.5~2倍左右的差距
input loop:50000000,iSamelen:4
loop:50000000,strcmp_asm,time:849 ms,strcmp_normal,time:1425 ms


input loop:50000000,iSamelen:2
loop:50000000,strcmp_asm,time:753 ms,strcmp_normal,time:1130 ms


input loop:50000000,iSamelen:1
loop:50000000,strcmp_asm,time:670 ms,strcmp_normal,time:1040 ms