struct timeval {
    union {
        long          tv_sec;         /* seconds */
        long          tv_secs;
    };
    union {
        long     tv_usec;        /* and microseconds */
        long     tv_micro;
    };
};

void timersub(struct timeval *a, struct timeval *b, struct timeval *res) {
	res->tv_sec = a->tv_sec - b->tv_sec;
	res->tv_usec = a->tv_usec - b->tv_usec;
	if (res->tv_usec < 0) {
		res->tv_sec--;
		res->tv_usec += 1000000;
	}
}