tv.c

/* vim: ft=c ff=unix fenc=utf-8
 * file: tv.c
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>
#include <inttypes.h>

#include <sys/time.h>


/* substract tv2 from tv1, result in tv1
 * if tv2 > tv1 result is tv1.tv_sec = 0, tv1.tv_usec = 0
 */
void
timeval_substract_tv(struct timeval *tv1, struct timeval *tv2)
{
	if (tv2->tv_usec > tv1->tv_usec) {
		if (tv1->tv_sec >= 1) {
			tv1->tv_sec--;
			tv1->tv_usec += 1000000;
		}
	}
	if (tv2->tv_sec > tv1->tv_sec || tv2->tv_usec > tv1->tv_usec) {
		tv1->tv_sec = 0u;
		tv1->tv_usec = 0u;
	} else {
		tv1->tv_sec -= tv2->tv_sec;
		tv1->tv_usec -= tv2->tv_usec;
	}
}

/* substract msec (milliseconds) from tv
 * if msec > tv result is tv.tv_sec = 0, tv.tv_usec = 0
 */
void
timeval_substract_msec(struct timeval *tv, unsigned msec)
{
	struct timeval tv2 = {};
	tv2.tv_sec = msec / 1000u;
	tv2.tv_usec = (msec % 1000u) * 1000u;
	timeval_substract_tv(tv, &tv2);
}

int
main(int argc, char *argv[])
{
	struct timeval tv1 = {};

	tv1.tv_sec = 2;
	tv1.tv_usec = 0;
	timeval_substract_msec(&tv1, 1000);
	printf("tv = %"PRIdPTR".%.06"PRIdPTR"\n", tv1.tv_sec, tv1.tv_usec);
	assert(tv1.tv_sec == 1 && tv1.tv_usec == 0);

	tv1.tv_sec = 1;
	tv1.tv_usec = 5000;
	timeval_substract_msec(&tv1, 1004);
	printf("tv = %"PRIdPTR".%.06"PRIdPTR"\n", tv1.tv_sec, tv1.tv_usec);
	assert(tv1.tv_sec == 0 && tv1.tv_usec == 1000);

	tv1.tv_sec = 4;
	tv1.tv_usec = 1000;
	timeval_substract_msec(&tv1, 4);
	printf("tv = %"PRIdPTR".%.06"PRIdPTR"\n", tv1.tv_sec, tv1.tv_usec);
	assert(tv1.tv_sec == 3 && tv1.tv_usec == 997000);

	tv1.tv_sec = 5;
	tv1.tv_usec = 2000;
	timeval_substract_msec(&tv1, 5400);
	printf("tv = %"PRIdPTR".%.06"PRIdPTR"\n", tv1.tv_sec, tv1.tv_usec);
	assert(tv1.tv_sec == 0 && tv1.tv_usec == 0);

	tv1.tv_sec = 0;
	tv1.tv_usec = 1000;
	timeval_substract_msec(&tv1, 2);
	printf("tv = %"PRIdPTR".%.06"PRIdPTR"\n", tv1.tv_sec, tv1.tv_usec);
	assert(tv1.tv_sec == 0 && tv1.tv_usec == 0);

	return EXIT_SUCCESS;
}