Function time_change

common/bolt12.c:449–473

}

static u64 time_change(u64 prevstart, u32 number,
		       void (*add_time)(struct tm *tm, u32 number),
		       bool day_const)
{
	struct tm tm;
	time_t prev = prevstart, ret;

	tm = *gmtime(&prev);

	for (;;) {
		struct tm new_tm = tm;
		add_time(&new_tm, number);
		ret = mktime(&new_tm);

		if (ret == (time_t)-1)
			return 0;

		/* If we overflowed that month, try one less. */
		if (!day_const || new_tm.tm_mday == tm.tm_mday)
			break;
		tm.tm_mday--;
	}

	return ret;
}

u64 offer_period_start(u64 basetime, size_t n,
		       const struct recurrence *recur)