usr.sbin/ndp/gmt2local.c

   1 /*      $OpenBSD: gmt2local.c,v 1.3 2008/10/02 23:55:18 deraadt Exp $   */
   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/types.h>
  25 #include <sys/time.h>
  26
  27 #include <stdio.h>
  28 #ifdef TIME_WITH_SYS_TIME
  29 #include <time.h>
  30 #endif
  31
  32 #include "gnuc.h"
  33 #ifdef HAVE_OS_PROTO_H
  34 #include "os-proto.h"
  35 #endif
  36
  37 #include "gmt2local.h"
  38
  39 /*
  40  * Returns the difference between gmt and local time in seconds.
  41  * Use gmtime() and localtime() to keep things simple.
  42  */
  43 int32_t
  44 gmt2local(time_t t)
  45 {
  46         register int dt, dir;
  47         register struct tm *gmt, *loc;
  48         struct tm sgmt;
  49
  50         if (t == 0)
  51                 t = time(NULL);
  52         gmt = &sgmt;
  53         *gmt = *gmtime(&t);
  54         loc = localtime(&t);
  55         dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 +
  56             (loc->tm_min - gmt->tm_min) * 60;
  57
  58         /*
  59          * If the year or julian day is different, we span 00:00 GMT
  60          * and must add or subtract a day. Check the year first to
  61          * avoid problems when the julian day wraps.
  62          */
  63         dir = loc->tm_year - gmt->tm_year;
  64         if (dir == 0)
  65                 dir = loc->tm_yday - gmt->tm_yday;
  66         dt += dir * 24 * 60 * 60;
  67
  68         return (dt);
  69 }