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gmt2local.c

/*
 * Copyright (c) 1997
 *    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.
 */

#ifndef lint
static const char rcsid[] =
    "@(#) $Header: gmt2local.c,v 1.2 97/01/23 22:31:25 leres Exp $ (LBL)";
#endif

#include <sys/types.h>
#include <sys/time.h>

#include <stdio.h>
#ifdef TIME_WITH_SYS_TIME
#include <time.h>
#endif

#include "gnuc.h"
#ifdef HAVE_OS_PROTO_H
#include "os-proto.h"
#endif

#include "gmt2local.h"

/*
 * Returns the difference between gmt and local time in seconds.
 * Use gmtime() and localtime() to keep things simple.
 */
int32_t
gmt2local(time_t t)
{
      register int dt, dir;
      register struct tm *gmt, *loc;
      struct tm sgmt;

      if (t == 0)
            t = time(NULL);
      gmt = &sgmt;
      *gmt = *gmtime(&t);
      loc = localtime(&t);
      dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
          (loc->tm_min - gmt->tm_min) * 60;

      /*
       * If the year or julian day is different, we span 00:00 GMT
       * and must add or subtract a day. Check the year first to
       * avoid problems when the julian day wraps.
       */
      dir = loc->tm_year - gmt->tm_year;
      if (dir == 0)
            dir = loc->tm_yday - gmt->tm_yday;
      dt += dir * 24 * 60 * 60;

      return (dt);
}

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