time/localtime.c

   1 /* Copyright (C) 1991, 1992, 1993 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <stddef.h>
  20 #include <ctype.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <time.h>
  25
  26
  27 /* Return the `struct tm' representation of *TIMER in the local timezone.  */
  28 struct tm *
  29 localtime (timer)
  30      const time_t *timer;
  31 {
  32   extern int __use_tzfile;
  33   extern int __tz_compute __P ((time_t timer, struct tm *tp));
  34   extern int __tzfile_compute __P ((time_t timer,
  35                                     long int *leap_correct, int *leap_hit));
  36   register struct tm *tp;
  37   long int leap_correction;
  38   int leap_extra_secs;
  39
  40   if (timer == NULL)
  41     {
  42       errno = EINVAL;
  43       return NULL;
  44     }
  45
  46   {
  47     /* Make sure the database is initialized.  */
  48     extern int __tzset_run;
  49     if (! __tzset_run)
  50       __tzset ();
  51   }
  52
  53   if (__use_tzfile)
  54     {
  55       if (! __tzfile_compute (*timer, &leap_correction, &leap_extra_secs))
  56         return NULL;
  57     }
  58   else
  59     {
  60       tp = gmtime (timer);
  61       if (tp == NULL)
  62         return NULL;
  63
  64       if (! __tz_compute (*timer, tp))
  65         return NULL;
  66
  67       leap_correction = 0L;
  68       leap_extra_secs = 0;
  69     }
  70
  71   tp = __offtime (timer, __timezone - leap_correction);
  72   tp->tm_sec += leap_extra_secs;
  73   tp->tm_isdst = __daylight;
  74   tp->tm_gmtoff = __timezone;
  75   tp->tm_zone = __tzname[__daylight];
  76   return tp;
  77 }