Programming

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <byteswap.h>
#include <sys/time.h>
 union   _U {
          unsigned int          in;
          struct _CH {
                  unsigned char c[4];
          } CH;
};
 int main(int argc, char *argv[])
{
  struct timeval t1, t2;
   union _U u;
  int   n;
  unsigned char tmp;
  
         u.in = (argc == 2) ? atoi(argv[1]) : 0xff;
         gettimeofday(&t1, NULL);
        for(n = 0; n < 100 * 1000000; n++)
        {
                u.in = n;

                 // Version 1
                u.in = bswap_32(u.in);

                 // Version 2 (homegrown)
                //tmp = u.CH.c[0];
                //u.CH.c[0] = u.CH.c[3];
                //u.CH.c[1] = u.CH.c[2];
                //u.CH.c[2] = u.CH.c[1];
                //u.CH.c[3] = tmp;
        }
        gettimeofday(&t2, NULL);
        printf("%lu mls\n", 
                (t2.tv_sec - t1.tv_sec) * 1000000 + (t2.tv_usec - t1.tv_usec));
        return(0);
}

cc -g

                 // Version 2 (homegrown)
                tmp = u.CH.c[0];
                u.CH.c[0] = u.CH.c[3];
                u.CH.c[3] = tmp;
                tmp = u.CH.c[1];
                u.CH.c[1] = u.CH.c[2];
                u.CH.c[2] = tmp;