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   1 /*
   2  * Copyright (c) 1997
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that: (1) source code distributions
   7  * retain the above copyright notice and this paragraph in its entirety, (2)
   8  * distributions including binary code include the above copyright notice and
   9  * this paragraph in its entirety in the documentation or other materials
  10  * provided with the distribution, and (3) all advertising materials mentioning
  11  * features or use of this software display the following acknowledgement:
  12  * ``This product includes software developed by the University of California,
  13  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
  14  * the University nor the names of its contributors may be used to endorse
  15  * or promote products derived from this software without specific prior
  16  * written permission.
  17  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
  18  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  19  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  20  */
  21
  22 #ifndef lint
  23 static const char rcsid[] =
  24     "@(#) $Header: /tcpdump/master/tcpdump/gmt2local.c,v 1.5 2002-06-01 23:43:34 guy Exp $ (LBL)";
  25 #endif
  26
  27 #ifdef HAVE_CONFIG_H
  28 #include "config.h"
  29 #endif
  30
  31 #include <sys/types.h>
  32
  33 #include <stdio.h>
  34 #include <time.h>
  35
  36 #ifdef HAVE_OS_PROTO_H
  37 #include "os-proto.h"
  38 #endif
  39
  40 #include "gmt2local.h"
  41
  42 /*
  43  * Returns the difference between gmt and local time in seconds.
  44  * Use gmtime() and localtime() to keep things simple.
  45  */
  46 int32_t
  47 gmt2local(time_t t)
  48 {
  49         register int dt, dir;
  50         register struct tm *gmt, *loc;
  51         struct tm sgmt;
  52
  53         if (t == 0)
  54                 t = time(NULL);
  55         gmt = &sgmt;
  56         *gmt = *gmtime(&t);
  57         loc = localtime(&t);
  58         dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
  59             (loc->tm_min - gmt->tm_min) * 60;
  60
  61         /*
  62          * If the year or julian day is different, we span 00:00 GMT
  63          * and must add or subtract a day. Check the year first to
  64          * avoid problems when the julian day wraps.
  65          */
  66         dir = loc->tm_year - gmt->tm_year;
  67         if (dir == 0)
  68                 dir = loc->tm_yday - gmt->tm_yday;
  69         dt += dir * 24 * 60 * 60;
  70
  71         return (dt);
  72 }