高效编程之指针跳转的影响

C语言的指针跳转访问是一个灵活高效的机制，但是再高效也是要花费额外时间的，下面这个程序如果在gcc -O0不优化的情况，就可以看出指针跳转比直接访问要多消耗10％左右的时间

#include <stdio.h>
#include <sys/time.h>
int main()
{
     int m = 0;
     int *p = &m;
     int i  =0;
     int n = 1;
     struct timeval time1, time2;


     m = 0;
     gettimeofday(&time1, 0);
     for(i = 0; i < 1000000000; i++)
     {
          *p = *p + n;
     }
     gettimeofday(&time2, 0);
     printf("time %f\n", (double)(time2.tv_sec-time1.tv_sec) + (double)(time2.tv_usec-time1.tv_usec) /1000000);


     m = 0;
     gettimeofday(&time1, 0);
     for(i = 0; i < 1000000000; i++)
     {
          m = m + n;
     }
     gettimeofday(&time2, 0);
     printf("time %f\n", (double)(time2.tv_sec-time1.tv_sec) + (double)(time2.tv_usec-time1.tv_usec) /1000000);


     printf("m %d\n", m);

     return 0;
}