Timer resolution and average behavior test

timetest.cpp

/*
 timetest.cpp
 
 A simple program to demonstrate the difference in timers on your platform.

 
 Tue Dec 21 15:11:06 CST 2010
 Chad Brewbaker
 crb002@gmail.com
 */


#include <stdio.h>
#include <time.h>
#include <sys/time.h>
#ifdef __APPLE__
#include <stdint.h>
#include <mach/mach_time.h>
#endif


int RUNS = 1000000;



double clock_res(unsigned* while_ticks){
	clock_t t1, t2;
	unsigned ticks =1;
	
	t1 = t2 = clock();
	
    // loop until t2 gets a different value
    while(t1 == t2)
	{t2 = clock(); ticks++;}
	
	*while_ticks = ticks;
    return (double)(t2 - t1) / CLOCKS_PER_SEC * 1000;
}



double gettimeofday_res(unsigned* while_ticks){
	timeval t1, t2;
    double elapsedTime;
	unsigned ticks = 1;
	
	gettimeofday(&t1, NULL);
	t2=t1;
	
	while( (t1.tv_usec == t2.tv_usec) &&  (t1.tv_sec == t2.tv_sec) ){
		gettimeofday(&t2, NULL);
		ticks++;
	}
	
    // compute and print the elapsed time in millisec
    elapsedTime = (t2.tv_sec - t1.tv_sec) * 1000.0;      // sec to ms
    elapsedTime += (t2.tv_usec - t1.tv_usec) / 1000.0;   // us to ms
    *while_ticks = ticks;
	return elapsedTime;	
}

#ifdef __APPLE__
double mach_res(unsigned* while_ticks){
	
	uint64_t t1, t2;
	unsigned ticks = 1;
	
	mach_timebase_info_data_t info;
	mach_timebase_info(&info);
	
	t1 = t2 = mach_absolute_time();
	
	/* Do some code */
	
	while( t1 == t2 )
	{t2 = mach_absolute_time(); ticks++;}
	
	
	uint64_t duration = t2 - t1;
	/* Convert to nanoseconds */
	duration *= info.numer;
	duration /= info.denom;
	
	*while_ticks = ticks;
	return (double) duration * 0.000001 ;
	
}
#endif

int main()
{
	int i;
	double total;
	double max;
	double res;
	unsigned ticks, min_ticks, max_ticks, tick_total;
	
	
	printf("Function_name \tave(ms) \tmax(ms) \tmin_ticks \tmax_ticks \tave_ticks\n");
	
	max_ticks = ticks = tick_total = 0;
	min_ticks = 1000000;
	total = max = 0.0;
	for(i=0; i<RUNS;i++){
		res = clock_res(&ticks);
		if(max < res)
			max = res;
		if(ticks > max_ticks)
			max_ticks = ticks;
		if(min_ticks > ticks)
			min_ticks = ticks;
		tick_total += ticks;
		total += res;
	} 
	printf("clock() \t%.10f \t%.10f \t%d \t%d \t%d\n", total/(double)RUNS, max, min_ticks, max_ticks, tick_total/RUNS);

	
	max_ticks = ticks = tick_total = 0;
	min_ticks = 1000000;
	total = max = 0.0;
	for(i=0; i<RUNS;i++){
		res = gettimeofday_res(&ticks);
		if(max < res)
			max = res;
		if(ticks > max_ticks)
			max_ticks = ticks;
		if(min_ticks > ticks)
			min_ticks = ticks;
		tick_total += ticks;
		total += res;
	} 
	printf("gettimeofday() \t%.10f \t%.10f  \t%d  \t%d  \t%d\n", total/(double)RUNS, max, min_ticks, max_ticks, tick_total/RUNS);
	
#ifdef __APPLE__
	max_ticks = ticks = tick_total = 0;
	min_ticks = 1000000;
	total = max = 0.0;
	for(i=0; i<RUNS;i++){
		res = mach_res(&ticks);
		if(max < res)
			max = res;
		if(ticks > max_ticks)
			max_ticks = ticks;
		if(min_ticks > ticks)
			min_ticks = ticks;
		tick_total += ticks;
		total += res;
	} 
	printf("mach_absolute_time() \t%.10f  \t%.10f  \t%d  \t%d \t%d\n", total/(double)RUNS, max, min_ticks, max_ticks, tick_total/RUNS);
#endif	
		
	
    return 0;
}

Output for a Core2Duo MacBook.

Function_name ave(ms) max(ms) min_ticks max_ticks ave_ticks
clock() 0.0013114960 0.0130000000 2 3 2
gettimeofday() 0.0010004230 0.1180000000 2 35 13
mach_absolute_time() 0.0000366985 0.0015940000 2 2 2