contrib/tcpdump/gmt2local.c

   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 #ifdef HAVE_CONFIG_H
  23 #include "config.h"
  24 #endif
  25
  26 #include <netdissect-stdinc.h>
  27
  28 #include <stdio.h>
  29
  30 #ifdef HAVE_OS_PROTO_H
  31 #include "os-proto.h"
  32 #endif
  33
  34 #include "gmt2local.h"
  35
  36 /*
  37  * Returns the difference between gmt and local time in seconds.
  38  * Use gmtime() and localtime() to keep things simple.
  39  */
  40 int32_t
  41 gmt2local(time_t t)
  42 {
  43         register int dt, dir;
  44         register struct tm *gmt, *loc;
  45         struct tm sgmt;
  46
  47         if (t == 0)
  48                 t = time(NULL);
  49         gmt = &sgmt;
  50         *gmt = *gmtime(&t);
  51         loc = localtime(&t);
  52         dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
  53             (loc->tm_min - gmt->tm_min) * 60;
  54
  55         /*
  56          * If the year or julian day is different, we span 00:00 GMT
  57          * and must add or subtract a day. Check the year first to
  58          * avoid problems when the julian day wraps.
  59          */
  60         dir = loc->tm_year - gmt->tm_year;
  61         if (dir == 0)
  62                 dir = loc->tm_yday - gmt->tm_yday;
  63         dt += dir * 24 * 60 * 60;
  64
  65         return (dt);
  66 }