path: root/time/mktime.c

/* Convert a `struct tm' to a time_t value.
   Copyright (C) 1993-1999, 2002, 2003 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Paul Eggert (eggert@twinsun.com).

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

/* Define this to have a standalone program to test this implementation of
   mktime.  */
/* #define DEBUG 1 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

/* Assume that leap seconds are possible, unless told otherwise.
   If the host has a `zic' command with a `-L leapsecondfilename' option,
   then it supports leap seconds; otherwise it probably doesn't.  */
#ifndef LEAP_SECONDS_POSSIBLE
# define LEAP_SECONDS_POSSIBLE 1
#endif

#include <sys/types.h>		/* Some systems define `time_t' here.  */
#include <time.h>

#include <limits.h>

#if DEBUG
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
/* Make it work even if the system's libc has its own mktime routine.  */
# define mktime my_mktime
#endif /* DEBUG */

/* The extra casts work around common compiler bugs.  */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
   It is necessary at least when t == time_t.  */
#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
			      ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))

#ifndef TIME_T_MIN
# define TIME_T_MIN TYPE_MINIMUM (time_t)
#endif
#ifndef TIME_T_MAX
# define TIME_T_MAX TYPE_MAXIMUM (time_t)
#endif

/* Verify a requirement at compile-time (unlike assert, which is runtime).  */
#define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }

verify (time_t_is_integer, (time_t) 0.5 == 0);
verify (twos_complement_arithmetic, -1 == ~1 + 1);
verify (right_shift_propagates_sign, -1 >> 1 == -1);
/* The code also assumes that signed integer overflow silently wraps
   around, but this assumption can't be stated without causing a
   diagnostic on some hosts.  */

#define EPOCH_YEAR 1970
#define TM_YEAR_BASE 1900
verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);

#ifndef __isleap
/* Nonzero if YEAR is a leap year (every 4 years,
   except every 100th isn't, and every 400th is).  */
# define __isleap(year)	\
  ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
#endif

/* How many days come before each month (0-12).  */
#ifndef _LIBC
static
#endif
const unsigned short int __mon_yday[2][13] =
  {
    /* Normal years.  */
    { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
    /* Leap years.  */
    { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
  };


#ifndef _LIBC
/* Portable standalone applications should supply a "time_r.h" that
   declares a POSIX-compliant localtime_r, for the benefit of older
   implementations that lack localtime_r or have a nonstandard one.
   See the gnulib time_r module for one way to implement this.  */
# include "time_r.h"
# undef __localtime_r
# define __localtime_r localtime_r
#endif


/* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
   measured in seconds, ignoring leap seconds.
   YEAR uses the same numbering as TM->tm_year.
   All values are in range, except possibly YEAR.
   If TP is null, return a nonzero value.
   If overflow occurs, yield the low order bits of the correct answer.  */
static time_t
ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
	       const struct tm *tp)
{
  if (!tp)
    return 1;
  else
    {
      verify (C99_integer_division, -1 / 2 == 0);

      /* Compute intervening leap days correctly even if year is negative.
	 Take care to avoid int overflow.  time_t overflow is OK, since
	 only the low order bits of the correct time_t answer are needed.
	 Don't convert to time_t until after all divisions are done, since
	 time_t might be unsigned.  */
      int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
      int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
      int a100 = a4 / 25 - (a4 % 25 < 0);
      int b100 = b4 / 25 - (b4 % 25 < 0);
      int a400 = a100 >> 2;
      int b400 = b100 >> 2;
      int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
      time_t years = year - (time_t) tp->tm_year;
      time_t days = (365 * years + intervening_leap_days
		     + (yday - tp->tm_yday));
      return (60 * (60 * (24