linux timing

double getUnixTime(void)
{
    struct timespec tv;

    if(clock_gettime(CLOCK_REALTIME, &tv) != 0) return 0;

    return (((double) tv.tv_sec) + (double) (tv.tv_nsec / 1000000000.0));
}

double start_time = getUnixTime();
double stop_time, difference;

algorithm();

stop_time = getUnixTime();
difference = stop_time - start_time;