timing.c

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

#ifdef __MACH__
#include <mach/clock.h>
#include <mach/mach.h>
#define CLOCK_REALTIME 0
#define CLOCK_MONOTONIC 0
static int 
clock_gettime(int clk_id, struct timespec *ts) {
	clock_serv_t cclock;
	mach_timespec_t mts;
	host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &cclock);
	clock_get_time(cclock, &mts);
	mach_port_deallocate(mach_task_self(), cclock);
	ts->tv_sec = mts.tv_sec;
	ts->tv_nsec = mts.tv_nsec;
	return 0;
}
#endif

void timespec_diff(struct timespec *start, struct timespec *stop,
	struct timespec *result)
{
	if ((stop->tv_nsec - start->tv_nsec) < 0) {
		result->tv_sec = stop->tv_sec - start->tv_sec - 1;
		result->tv_nsec = stop->tv_nsec - start->tv_nsec + 1000000000;
	} else {
		result->tv_sec = stop->tv_sec - start->tv_sec;
		result->tv_nsec = stop->tv_nsec - start->tv_nsec;
	}
}

timespec ts1, ts2;
clock_gettime(CLOCK_REALTIME, &ts1);
// do something
clock_gettime(CLOCK_REALTIME, &ts2);
timespec diff;
timespec_diff(&ts1, &ts2, &diff);
printf("%lld.%.9ld\n", diff.tv_nsec - diff.tv_nsec);