#include <stdio.h>
#include <time.h>
#include <sys/time.h>
#include <sys/times.h>
#include <errno.h>
#include <string.h>

#define MAXVAL 1000
#define NCLOCKREADS 100

/* consider adding check on precision of gettimeofday,
   then check on precision of timers, then check
   on precision of thread scheduling */

int main () 
{ time_t t0, t1, t2;
  int count[MAXVAL];
  long d, d_sec, d_usec;
  int i;
  struct timeval tv1, tv2;
  struct tms buffer;

  memset (val, 0, sizeof (val));
  if (gettimeofday (&tv1, NULL)) {
    perror ("gettimeofday");
  }
  t0 = t1 = times(&buffer);
  do {
    for (i = 0; i<NCLOCKREADS; i++) {
      t2 = times(&buffer);
      d = (long) (t2 - t1);
      if (d > MAXVAL) d = MAXVAL-1;
      count[(int) d]++;
      t1 = t2;
    }
    if (gettimeofday (&tv2, NULL)) {
      perror ("gettimeofday");
    }
    d_sec = tv2.tv_sec - tv1.tv_sec;
    d_usec = tv2.tv_usec - tv1.tv_usec + 1000000*d_sec;
  } while (d_usec < 1000000);

  printf ("elapsed time = %ld usec\n", d_usec);
  printf ("elapsed ticks = %ld\n", (long)(t2-t0));
  printf ("ticks per second = %10ld\n", (long)(t2-t0));

  printf("ticks frequency\n----- --------\n");
  for (i = 0; i < MAXVAL; i++) {
    if (count[i]) printf ("%5d %5d\n", i, count[i]);
  }
  return 0;
}