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 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

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;i1)
    {
        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