time/localtime.c

   1 /* localtime -- convert `time_t' to `struct tm' in local time zone
   2 Copyright (C) 1991, 92, 93, 95, 96 Free Software Foundation, Inc.
   3 This file is part of the GNU C Library.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 License, or (at your option) any later version.
   9
  10 The GNU C Library is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #include <errno.h>
  21 #include <time.h>
  22 #include <libc-lock.h>
  23
  24 /* The C Standard says that localtime and gmtime return the same pointer.  */
  25 struct tm _tmbuf;
  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   return __localtime_r (timer, &_tmbuf);
  33 }
  34
  35 struct tm *
  36 __localtime_r (timer, tp)
  37      const time_t *timer;
  38      struct tm *tp;
  39 {
  40   /* This lock is defined in tzset.c and locks all the data defined there
  41      and in tzfile.c; the internal functions do no locking themselves.
  42      This lock is only taken here and in `tzset'.  */
  43   __libc_lock_define (extern, __tzset_lock)
  44   extern int __tzset_run, __use_tzfile;
  45   extern int __tz_compute __P ((time_t timer, struct tm *tp));
  46   extern int __tzfile_compute __P ((time_t timer,
  47                                     long int *leap_correct, int *leap_hit));
  48   long int leap_correction;
  49   int leap_extra_secs;
  50
  51   if (timer == NULL)
  52     {
  53       errno = EINVAL;
  54       return NULL;
  55     }
  56
  57   __libc_lock_lock (__tzset_lock);
  58
  59   /* Make sure the database is initialized.  */
  60   if (! __tzset_run)
  61     __tzset ();
  62
  63   if (__use_tzfile)
  64     {
  65       if (! __tzfile_compute (*timer, &leap_correction, &leap_extra_secs))
  66         tp = NULL;
  67     }
  68   else
  69     {
  70       tp = __gmtime_r (timer, tp);
  71       if (tp && ! __tz_compute (*timer, tp))
  72         tp = NULL;
  73       leap_correction = 0L;
  74       leap_extra_secs = 0;
  75     }
  76
  77   if (tp)
  78     {
  79       __offtime (timer, __timezone - leap_correction, tp);
  80       tp->tm_sec += leap_extra_secs;
  81       tp->tm_isdst = __daylight;
  82       tp->tm_gmtoff = __timezone;
  83       tp->tm_zone = __tzname[__daylight];
  84     }
  85
  86   __libc_lock_unlock (__tzset_lock);
  87
  88   return tp;
  89 }
  90 weak_alias (__localtime_r, localtime_r)