返回一段程序经过的CPU周期数

1,实例代码:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static unsigned cyc_high=0;
static unsigned cyc_low=0;

//rstsc指令访问计数器,高32为保存在%edx,低32位保存在%ax
void access_counter( unsigned* hi, unsigned* lo )
{
    asm("rdtsc; movl %%edx,%0; movl %%eax,%1"
        :"=r" (*hi),"=r" (*lo)
        :
        : "%edx", "%eax");
}

void start_counter()
{
    access_counter( &cyc_high, &cyc_low );
}

double get_counter()
{
    unsigned ncyc_high,ncyc_low;
    unsigned high_num,low_num,borrow;
    double result;

    access_counter( &ncyc_high, &ncyc_low );
    low_num=ncyc_low-cyc_low;
    borrow=( low_num<0 );
    high_num=ncyc_high-cyc_high;
    result=(double)high_num*(1<<30)*4+low_num;
    if(result<0)
        fprintf(stderr,"Error: counter returns neg value: %.0f\n",result);
    return result;
}


double get_mhz(int sleeptime)
{
    double rate;
    start_counter();
    sleep(sleeptime);
    rate=get_counter()/(1e6*sleeptime);
    return rate;
}




int main()
{
    double mhz;
    mhz=get_mhz(3);
    printf("CPU Time Frequency: %.0f MHZ\n",mhz);

    start_counter();
    //测量代码段
    printf("%.0f",get_counter());
    return 0;
}