time/timegm.c

   1 /* Convert UTC calendar time to simple time.  Like mktime but assumes UTC.
   2
   3    Copyright (C) 1994-2017 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #ifdef HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #ifdef _LIBC
  25 # include <time.h>
  26 #else
  27 # include "timegm.h"
  28
  29 /* Portable standalone applications should supply a "time_r.h" that
  30    declares a POSIX-compliant gmtime_r, for the benefit of older
  31    implementations that lack gmtime_r or have a nonstandard one.
  32    See the gnulib time_r module for one way to implement this.  */
  33 # include <time_r.h>
  34 # undef __gmtime_r
  35 # define __gmtime_r gmtime_r
  36 time_t __mktime_internal (struct tm *,
  37                           struct tm * (*) (time_t const *, struct tm *),
  38                           time_t *);
  39 #endif
  40
  41 time_t
  42 timegm (struct tm *tmp)
  43 {
  44   static time_t gmtime_offset;
  45   tmp->tm_isdst = 0;
  46   return __mktime_internal (tmp, __gmtime_r, &gmtime_offset);
  47 }