path: root/time/mktime.c

/* Convert a 'struct tm' to a time_t value.
   Copyright (C) 1993-2016 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, see
   <http://www.gnu.org/licenses/>.  */

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

#ifndef _LIBC
# 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 <time.h>

#include <limits.h>

#include <string.h>		/* For the real memcpy prototype.  */

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

/* Some of the code in this file assumes that signed integer overflow
   silently wraps around.  This assumption can't easily be programmed
   around, nor can it be checked for portably at compile-time or
   easily eliminated at run-time.

   Define WRAPV to 1 if the assumption is valid and if
     #pragma GCC optimize ("wrapv")
   does not trigger GCC bug 51793
   <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51793>.
   Otherwise, define it to 0; this forces the use of slower code that,
   while not guaranteed by the C Standard, works on all production
   platforms that we know about.  */
#ifndef WRAPV
# if (((__GNUC__ == 4 && 4 <= __GNUC_MINOR__) || 4 < __GNUC__) \
      && defined __GLIBC__)
#  pragma GCC optimize ("wrapv")
#  define WRAPV 1
# else
#  define WRAPV 0
# endif
#endif

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

/* A signed type that is at least one bit wider than int.  */
#if INT_MAX <= LONG_MAX / 2
typedef long int long_int;
#else
typedef long long int long_int;
#endif
verify (long_int_is_wide_enough, INT_MAX == INT_MAX * (long_int) 2 / 2);

/* Shift A right by B bits portably, by dividing A by 2**B and
   truncating towards minus infinity.  A and B should be free of side
   effects, and B should be in the range 0 <= B <= INT_BITS - 2, where
   INT_BITS is the number of useful bits in an int.  GNU code can
   assume that INT_BITS is at least 32.

   ISO C99 says that A >> B is implementation-defined if A < 0.  Some
   implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift
   right in the usual way when A < 0, so SHR falls back on division if
   ordinary A >> B doesn't seem to be the usual signed shift.  */
#define SHR(a, b)                                               \
  ((-1 >> 1 == -1                                               \
    && (long_int) -1 >> 1 == -1                                 \
    && ((time_t) -1 >> 1 == -1 || ! TYPE_SIGNED (time_t)))      \
   ? (a) >> (b)                                                 \
   : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0))

/* The extra casts in the following macros work around compiler bugs,
   e.g., in Cray C 5.0.3.0.  */

/* True if the arithmetic type T is an integer type.  bool counts as
   an integer.  */
#define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)

/* True if negative values of the signed integer type T use two's
   complement, or if T is an unsigned integer type.  */
#define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)

/* True if the arithmetic type T is signed.  */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))

/* The maximum and minimum values for the integer type T.  These
   macros have undefined behavior if T is signed and has padding bits.
   If this is a problem for you, please let us know how to fix it for
   your host.  */
#define TYPE_MINIMUM(t) \
  ((t) (! TYPE_SIGNED (t) \
	? (t) 0 \
	: ~ TYPE_MAXIMUM (t)))
#define TYPE_MAXIMUM(t) \
  ((t) (! TYPE_SIGNED (t) \
	? (t) -1 \
	: ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))

#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
#define TIME_T_MIDPOINT (SHR (TIME_T_MIN + TIME_T_MAX, 1) + 1)

verify (time_t_is_integer, TYPE_IS_INTEGER (time_t));
verify (twos_complement_arithmetic,
	(TYPE_TWOS_COMPLEMENT (int)
	 && TYPE_TWOS_COMPLEMENT (long_int)
	 && TYPE_TWOS_COMPLEMENT (time_t)));

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

/* Return 1 if YEAR + TM_YEAR_BASE is a leap year.  */
static int
leapyear (long_int year)
{
  /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
     Also, work even if YEAR is negative.  */
  return
    ((year & 3) == 0
     && (year % 100 != 0
	 || ((year / 100) & 3) == (-