#include <unistd.h>		// symbolic constants
#include <stdlib.h>		// general utilities
#include <stdio.h>		// printf
#include <sys/time.h>		// gettimeofday
#include <sys/types.h>		// wait
#include <sys/wait.h>		// wait

//
// Purpose:	Measure the average execution times of:
//			o the stub function call
//			o the system call gettimeofday(2)
//			o the fork(2) system call
//		using gettimeofday.  Run each case 3 times.
//
// Usage:	timeit > timeit.out			# produce raw data
//
// Output:	The output lines are marked with a letter to indicate the
//		call being timed:
//			'S' for the stub function call
//			'G' for the gettimeofday call
//			'F' for the fork call
//	For example:
//	S  10000	0.004400	(1170266760, 781009)	(1170266760, 781053)
//	means that the output is for the stub function call where N = 1000,
//	tavg = 0.004400 usec.  The parenthesized values are the tbegin and tend
//	values
//
// Build:	g++ -o timeit timeit.c
//

const int LIMIT = 10000;			// limit on N
const int M = 1000000;

void stub (void) {	/* null function */ 	}

static inline pid_t
Fork(void) {
  pid_t		pid;
  if ((pid=fork()) < 0) { perror(""); exit(1); }
  return pid;
}

static inline pid_t
Waitpid(pid_t pid, int *status, int options) {
  if (wait(status) != pid) { perror(""); exit(1); }
  return pid;
}

int
main (int argc, char *argv[]) {
  enum { STUB=0, GETTOD, FORK };
  const char which[3] = { 'S', 'G', 'F' };

  setlinebuf(stdout);		// VERY important to avoid output confusion
  system("uptime");

  for (int i=0; i<3; i++) {		// each call type
    for (int N=10; N<=LIMIT; N*=10) {		// N = 10, 100, ... , LIMIT
      double	tavg;

      for (int j=0; j<3; j++) {		// do 3 times
	if (i == STUB) {
	  for (int k=0; k<N; k++) { stub(); }
	} else if (i == GETTOD) {
	  for (int k=0; k<N; k++) {
	    struct timeval	x;
	    gettimeofday(&x,0);
	  }
	} else {
	  for (int k=0; k<N; k++) {
	    pid_t	cpid;
	    int		stat;
	    int		rc;
	    if ( (cpid=Fork()) == 0 )	exit(0);
	    Waitpid(cpid, &stat, 0);
	  }
	}
	tavg = ...	// in usec
	printf ("%c\t%7d\t%f\t(%ld, %ld)\t(%ld, %ld)\n",
			which[i], N, tavg,
			tbegin.tv_sec, tbegin.tv_usec, tend.tv_sec, tend.tv_usec);
      }
    }
  }
  system("uptime");

  return 0;
}