dist/tcpdump/gmt2local.c

   1 /*      $NetBSD$        */
   2
   3 /*
   4  * Copyright (c) 1997
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that: (1) source code distributions
   9  * retain the above copyright notice and this paragraph in its entirety, (2)
  10  * distributions including binary code include the above copyright notice and
  11  * this paragraph in its entirety in the documentation or other materials
  12  * provided with the distribution, and (3) all advertising materials mentioning
  13  * features or use of this software display the following acknowledgement:
  14  * ``This product includes software developed by the University of California,
  15  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
  16  * the University nor the names of its contributors may be used to endorse
  17  * or promote products derived from this software without specific prior
  18  * written permission.
  19  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
  20  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  21  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  22  */
  23
  24 #include <sys/cdefs.h>
  25 #ifndef lint
  26 #if 0
  27 static const char rcsid[] _U_ =
  28     "@(#) Header: /tcpdump/master/tcpdump/gmt2local.c,v 1.9 2003/11/16 09:36:09 guy Exp (LBL)";
  29 #else
  30 __RCSID("$NetBSD: tcpdump2rcsid.ex,v 1.1 2001/06/25 20:09:58 itojun Exp $");
  31 #endif
  32 #endif
  33
  34 #ifdef HAVE_CONFIG_H
  35 #include "config.h"
  36 #endif
  37
  38 #include <tcpdump-stdinc.h>
  39
  40 #include <stdio.h>
  41
  42 #ifdef HAVE_OS_PROTO_H
  43 #include "os-proto.h"
  44 #endif
  45
  46 #include "gmt2local.h"
  47
  48 /*
  49  * Returns the difference between gmt and local time in seconds.
  50  * Use gmtime() and localtime() to keep things simple.
  51  */
  52 int32_t
  53 gmt2local(time_t t)
  54 {
  55         register int dt, dir;
  56         register struct tm *gmt, *loc;
  57         struct tm sgmt;
  58
  59         if (t == 0)
  60                 t = time(NULL);
  61         gmt = &sgmt;
  62         *gmt = *gmtime(&t);
  63         loc = localtime(&t);
  64         dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
  65             (loc->tm_min - gmt->tm_min) * 60;
  66
  67         /*
  68          * If the year or julian day is different, we span 00:00 GMT
  69          * and must add or subtract a day. Check the year first to
  70          * avoid problems when the julian day wraps.
  71          */
  72         dir = loc->tm_year - gmt->tm_year;
  73         if (dir == 0)
  74                 dir = loc->tm_yday - gmt->tm_yday;
  75         dt += dir * 24 * 60 * 60;
  76
  77         return (dt);
  78 }