/*
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * $FreeBSD: src/usr.sbin/tcpdump/tcpslice/gwtm2secs.c,v 1.4 1999/08/28 05:11:32 peter Exp $
 * $DragonFly: src/usr.sbin/tcpdump/tcpslice/gwtm2secs.c,v 1.4 2005/12/05 02:40:28 swildner Exp $
 */

/*
 * gwtm2secs.c - convert "tm" structs for Greenwich time to Unix timestamp
 */

#include "tcpslice.h"

static int days_in_month[] =
	/* Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec */
	{  31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

#define IS_LEAP_YEAR(year)	\
	(year % 4 == 0 && (year % 100 != 0 || year % 400 == 0))

time_t
gwtm2secs(struct tm *tm)
{
	int i, days, year;

	year = tm->tm_year;

	/*
	 * Allow for year being specified with either 2 digits or 4 digits.
	 * 2-digit years are either 19xx or 20xx - a simple heuristic
	 * distinguishes them, since we can't represent any time < 1970.
	 */
	if (year < 100) {
		if (year >= 70)
			year += 1900;
		else
			year += 2000;
	}

	days = 0;
	for (i = 1970; i < year; ++i) {
		days += 365;
		if (IS_LEAP_YEAR(i))
			++days;
	}

	for (i = 0; i < tm->tm_mon; ++i)
		days += days_in_month[i];

	if (IS_LEAP_YEAR(year) && tm->tm_mon > 1)	/* 1 is February */
		++days;

	days += tm->tm_mday - 1; /* -1 since days are numbered starting at 1 */

	return(days * 86400 + tm->tm_hour * 3600 + tm->tm_min * 60 + tm->tm_sec);
}