#include <time.h>

static int
leapyear(int year)
{
	return ((year % 4) == 0 && ((year % 100) != 0 || (year % 400) == 0));
}

/*
 * This is a simple implementation of timegm() which does what is needed
 * by parse-time-string.c -- just turns the "struct tm" into a GMT time_t.
 * It does not normalize any of the fields of the "struct tm", nor does
 * it set tm_wday or tm_yday.
 */
static time_t
timegm(struct tm *tm)
{
	int	monthlen[2][12] = {
		{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
		{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
	};
	int	year, month, days;

	days = 365 * (tm->tm_year - 70);
	for (year = 70; year < tm->tm_year; year++) {
		if (leapyear(1900 + year)) {
			days++;
		}
	}
	for (month = 0; month < tm->tm_mon; month++) {
		days += monthlen[leapyear(1900 + year)][month];
	}
	days += tm->tm_mday - 1;

	return ((((days * 24) + tm->tm_hour) * 60 + tm->tm_min) * 60 +
	    tm->tm_sec);
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void
tm_test(int niter)
{
	const int	monthlen[2][12] = {
		{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
		{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
	};
	int		i;
	struct tm	tm, *tmp;
	time_t		t;

	for (i = 0; i < niter; i++) {
		tm.tm_year = (lrand48() % 67) + 70;
		tm.tm_mon = lrand48() % 12;
		do {
			t = (lrand48() % 31) + 1;
		} while (t > monthlen[leapyear(1900 + tm.tm_year)][tm.tm_mon]);
		tm.tm_mday = t;
		tm.tm_hour = lrand48() % 24;
		tm.tm_min = lrand48() % 60;
		tm.tm_sec = lrand48() % 60;

		t = timegm(&tm);
		tmp = gmtime(&t);

		if (tmp->tm_sec != tm.tm_sec ||
		    tmp->tm_min != tm.tm_min ||
		    tmp->tm_hour != tm.tm_hour ||
		    tmp->tm_mday != tm.tm_mday ||
		    tmp->tm_mon != tm.tm_mon ||
		    tmp->tm_year != tm.tm_year) {
			printf("%4d-%02d-%02d %02d:%02d:%02d -> "
			    "%4d-%02d-%02d %02d:%02d:%02d\n",
			    tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
			    tm.tm_hour, tm.tm_min, tm.tm_sec,
			    tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday,
			    tmp->tm_hour, tmp->tm_min, tmp->tm_sec);

		}
	}
}

void
time_test(int niter)
{
	int		i;
	time_t		st, et;
	struct tm	*tmp;

	for (i = 0; i < niter; i++) {
		st = (time_t)lrand48();

		tmp = gmtime(&st);
		et = timegm(tmp);

		if (st != et) {
			printf("%d -> %d (%4d-%02d-%02d %02d:%02d:%02d)\n",
			    st, et,
			    tmp->tm_year + 1900, tmp->tm_mon + 1, tmp->tm_mday,
			    tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
		}
	}
}

int
main(void)
{
	const int	niter = 10000000;

	srand48(getpid());

	tm_test(niter);
	time_test(niter);

	return (0);
}