/*
** $Id: timing.c 819 2008-03-09 17:41:59Z phf $
**
** Example for using time(3) and gettimeofday(2) to measure
** performance of pieces of code. You should probably use
** gprof instead, but hey... :-)
**
** Note that (on my machine) the timeval microseconds stuff
** sometimes returns crazy values; apparently you sometimes
** need to "round" those into the seconds field, but I won't
** bother here. For example, I found this piece of code on
** the net that explains better what I mean:
**
** // resolve seconds carry
** static inline void update_tv(struct timeval *t1)
** {
**   if (t1->tv_usec >= MILLION_I) {
**     t1->tv_sec++;
**     t1->tv_usec -= MILLION_I;
**   }
**   if (t1->tv_usec < 0) {
**     t1->tv_sec--;
**     t1->tv_usec += MILLION_I;
**   }
** }
**
** However, I could not find "proper" documentation on this
** anywhere... :-/ If you find something, let me know! :-)
*/

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <sys/time.h>

// just some code that runs a little while, if your machine
// is faster, adjust the numbers... :-)
void bla(void)
{
  for (long i = 0; i < 0x07ffffff; i++) {
    // bla
  }
}

// not very exact: using time(3) function, seconds accuracy
int timet(void)
{
  time_t before, after;
  before = time(NULL);
  bla();
  after = time(NULL);
  return after-before;
}

// much more exact: using gettimeofday(2) function, closer
// to microseconds accuracy (but never really quite that)
struct timeval timeg(void)
{
  struct timeval before, after, difference;

  (void) gettimeofday(&before, NULL);
  bla();
  (void) gettimeofday(&after, NULL);

  difference.tv_sec = after.tv_sec - before.tv_sec;
  difference.tv_usec = after.tv_usec - before.tv_usec;
  return difference;
}

int main(void)
{
  printf("time(3) says: %d seconds\n", timet());

  struct timeval time = timeg();

  printf("gettimeofday(2) says: %ld seconds %ld microseconds\n",
         time.tv_sec, time.tv_usec);

  return EXIT_SUCCESS;
}