/* Copyright (c) 2002-2003 Timo Sirainen */

#include "lib.h"

#include "utc-offset.h"

#include <sys/time.h>

int utc_offset(struct tm *tm, time_t t __attr_unused__)

{

#ifdef HAVE_TM_GMTOFF

	return (int) (tm->tm_gmtoff/60);

#else

	struct tm ltm, gtm;

	int offset;

	/* gmtime() overwrites tm, so we need to copy it elsewhere */

	ltm = *tm;

	tm = gmtime(&t);

	gtm = *tm;

	/* max offset of 24 hours */

	if ((ltm.tm_yday < gtm.tm_yday && ltm.tm_year == gtm.tm_year) ||

	    ltm.tm_year < gtm.tm_year)

		offset = -24 * 60;

	else if ((ltm.tm_yday > gtm.tm_yday && ltm.tm_year == gtm.tm_year) ||

		 ltm.tm_year > gtm.tm_year)

		offset = 24 * 60;

	else

		offset = 0;

	offset += (ltm.tm_hour - gtm.tm_hour) * 60;

	offset += (ltm.tm_min - gtm.tm_min);

	/* restore overwritten tm */

	*tm = ltm;

	return offset;

#endif

}