glibc/time/localtime.c

/* localtime -- convert `time_t' to `struct tm' in local time zone
Copyright (C) 1991, 92, 93, 95, 96 Free Software Foundation, Inc.
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <errno.h>
#include <time.h>
#include <libc-lock.h>

/* The C Standard says that localtime and gmtime return the same pointer.  */
struct tm _tmbuf;

/* Return the `struct tm' representation of *TIMER in the local timezone.  */
struct tm *
localtime (timer)
     const time_t *timer;
{
  return __localtime_r (timer, &_tmbuf);
}

struct tm *
__localtime_r (timer, tp)
     const time_t *timer;
     struct tm *tp;
{
  /* This lock is defined in tzset.c and locks all the data defined there
     and in tzfile.c; the internal functions do no locking themselves.
     This lock is only taken here and in `tzset'.  */
  __libc_lock_define (extern, __tzset_lock)
  extern int __use_tzfile;
  extern int __tz_compute __P ((time_t timer, struct tm *tp));
  extern int __tzfile_compute __P ((time_t timer,
				    long int *leap_correct, int *leap_hit));
  long int leap_correction;
  int leap_extra_secs;

  if (timer == NULL)
    {
      __set_errno (EINVAL);
      return NULL;
    }

  __libc_lock_lock (__tzset_lock);

  /* Make sure the database is initialized.  */
  __tzset ();

  if (__use_tzfile)
    {
      if (! __tzfile_compute (*timer, &leap_correction, &leap_extra_secs))
	tp = NULL;
    }
  else
    {
      tp = __gmtime_r (timer, tp);
      if (tp && ! __tz_compute (*timer, tp))
	tp = NULL;
      leap_correction = 0L;
      leap_extra_secs = 0;
    }

  if (tp)
    {
      __offtime (timer, __timezone - leap_correction, tp);
      tp->tm_sec += leap_extra_secs;
      tp->tm_isdst = __daylight;
      tp->tm_gmtoff = __timezone;
      tp->tm_zone = __tzname[__daylight];
    }

  __libc_lock_unlock (__tzset_lock);

  return tp;
}
weak_alias (__localtime_r, localtime_r)