ftimer.c

/*
 * ftimer.c - Estimate the time (in seconds) used by a function f
 *
 * Copyright (c) 2002, R. Bryant and D. O'Hallaron, All rights reserved.
 * May not be used, modified, or copied without permission.
 *
 * Function timers that estimate the running time (in seconds) of a function f.
 *    ftimer_itimer: version that uses the interval timer
 *    ftimer_gettod: version that uses gettimeofday
 */
#include <stdio.h>
#include <sys/time.h>
#include "ftimer.h"

/* function prototypes */
static void init_etime(void);
static double get_etime(void);

/*
 * ftimer_itimer - Use the interval timer to estimate the running time
 * of f(argp). Return the average of n runs.
 */
double ftimer_itimer(ftimer_test_funct f, void *argp, int n)
{
  double start, tmeas;
  int i;

  init_etime();
  start = get_etime();
  for (i = 0; i < n; i++)
    f(argp);
  tmeas = get_etime() - start;
  return tmeas / n;
}

/*
 * ftimer_gettod - Use gettimeofday to estimate the running time of
 * f(argp). Return the average of n runs.
 */
double ftimer_gettod(ftimer_test_funct f, void *argp, int n)
{
  int i;
  struct timeval stv, etv;
  double diff;

  gettimeofday(&stv, NULL);
  for (i = 0; i < n; i++)
    f(argp);
  gettimeofday(&etv,NULL);
  diff = 1E3*(etv.tv_sec - stv.tv_sec) + 1E-3*(etv.tv_usec-stv.tv_usec);
  diff /= n;
  return (1E-3*diff);
}


/*
 * Routines for manipulating the Unix interval timer
 */

/* The initial value of the interval timer */
#define MAX_ETIME 86400

/* static variables that hold the initial value of the interval timer */
static struct itimerval first_u; /* user time */
static struct itimerval first_r; /* real time */
static struct itimerval first_p; /* prof time*/

/* init the timer */
static void init_etime(void)
{
  first_u.it_interval.tv_sec = 0;
  first_u.it_interval.tv_usec = 0;
  first_u.it_value.tv_sec = MAX_ETIME;
  first_u.it_value.tv_usec = 0;
  setitimer(ITIMER_VIRTUAL, &first_u, NULL);

  first_r.it_interval.tv_sec = 0;
  first_r.it_interval.tv_usec = 0;
  first_r.it_value.tv_sec = MAX_ETIME;
  first_r.it_value.tv_usec = 0;
  setitimer(ITIMER_REAL, &first_r, NULL);

  first_p.it_interval.tv_sec = 0;
  first_p.it_interval.tv_usec = 0;
  first_p.it_value.tv_sec = MAX_ETIME;
  first_p.it_value.tv_usec = 0;
  setitimer(ITIMER_PROF, &first_p, NULL);
}

/* return elapsed real seconds since call to init_etime */
static double get_etime(void)
{
  struct itimerval v_curr;
  struct itimerval r_curr;
  struct itimerval p_curr;

  getitimer(ITIMER_VIRTUAL, &v_curr);
  getitimer(ITIMER_REAL,&r_curr);
  getitimer(ITIMER_PROF,&p_curr);

  return (double) ((first_p.it_value.tv_sec - r_curr.it_value.tv_sec) +
                   (first_p.it_value.tv_usec - r_curr.it_value.tv_usec)*1e-6);
}