mktime.c

简单的时间处理类 希望有帮助 谢谢 简单的时间处理类 希望有帮助 谢谢

/* Convert a `struct tm' to a time_t value.
   Copyright (C) 1993-1999, 2002-2005, 2006 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Paul Eggert <[e-mail]>.

   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>

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

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

/* 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	\
   ? (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, ones' complement, or signed magnitude representation,
   respectively.  Much GNU code assumes two's complement, but some
   people like to be portable to all possible C hosts.  */
#define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
#define TYPE_ONES_COMPLEMENT(t) ((t) ~ (t) 0 == 0)
#define TYPE_SIGNED_MAGNITUDE(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_SIGNED_MAGNITUDE (t) \
	? ~ (t) 0 \
	: ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
#define TYPE_MAXIMUM(t) \
  ((t) (! TYPE_SIGNED (t) \
	? (t) -1 \
	: ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 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 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, TYPE_IS_INTEGER (time_t));
verify (twos_complement_arithmetic, TYPE_TWOS_COMPLEMENT (int));
/* 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);

/* Return 1 if YEAR + TM_YEAR_BASE is a leap year.  */
static inline 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) == (- (TM_YEAR_BASE / 100) & 3)));
}

/* 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
# define __mktime_internal mktime_internal
#endif

/* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
   (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
   were not adjusted between the time stamps.

   The YEAR values uses the same numbering as TP->tm_year.  Values
   need not be in the usual range.  However, YEAR1 must not be less
   than 2 * INT_MIN or greater than 2 * INT_MAX.

   The result may overflow.  It is the caller's responsibility to
   detect overflow.  */

static inline time_t
ydhms_diff (long int year1, long int yday1, int hour1, int min1, int sec1,
	    int year0, int yday0, int hour0, int min0, int sec0)
{
  verify (C99_integer_division, -1 / 2 == 0);
  verify (long_int_year_and_yday_are_wide_enough,
	  INT_MAX <= LONG_MAX / 2 || TIME_T_MAX <= UINT_MAX);

  /* Compute intervening leap days correctly even if year is negative.
     Take care to avoid integer overflow here.  */
  int a4 = SHR (year1, 2) + SHR (TM_YEAR_BASE, 2) - ! (year1 & 3);
  int b4 = SHR (year0, 2) + SHR (TM_YEAR_BASE, 2) - ! (year0 & 3);
  int a100 = a4 / 25 - (a4 % 25 < 0);
  int b100 = b4 / 25 - (b4 % 25 < 0);
  int a400 = SHR (a100, 2);
  int b400 = SHR (b100, 2);
  int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);

  /* Compute the desired time in time_t precision.  Overflow might
     occur here.  */
  time_t tyear1 = year1;
  time_t years = tyear1 - year0;
  time_t days = 365 * years + yday1 - yday0 + intervening_leap_days;
  time_t hours = 24 * days + hour1 - hour0;
  time_t minutes = 60 * hours + min1 - min0;
  time_t seconds = 60 * minutes + sec1 - sec0;
  return seconds;
}


/* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC),
   assuming that *T corresponds to *TP and that no clock adjustments
   occurred between *TP and the desired time.
   If TP is null, return a value not equal to *T; this avoids false matches.
   If overflow occurs, yield the minimal or maximal value, except do not
   yield a value equal to *T.  */
static time_t
guess_time_tm (long int year, long int yday, int hour, int min, int sec,
	       const time_t *t, const struct tm *tp)
{
  if (tp)
    {
      time_t d = ydhms_diff (year, yday, hour, min, sec,
			     tp->tm_year, tp->tm_yday,
			     tp->tm_hour, tp->tm_min, tp->tm_sec);
      time_t t1 = *t + d;
      if ((t1 < *t) == (TYPE_SIGNED (time_t) ? d < 0 : TIME_T_MAX / 2 < d))
	return t1;
    }

  /* Overflow occurred one way or another.  Return the nearest result
     that is actually in range, except don't report a zero difference
     if the actual difference is nonzero, as that would cause a false
     match; and don't oscillate between two values, as that would
     confuse the spring-forward gap detector.  */
  return (*t < TIME_T_MIDPOINT
	  ? (*t <= TIME_T_MIN + 1 ? *t + 1 : TIME_T_MIN)
	  : (TIME_T_MAX - 1 <= *t ? *t - 1 : TIME_T_MAX));
}

/* Use CONVERT to convert *T to a broken down time in *TP.
   If *T is out of range for conversion, adjust it so that
   it is the nearest in-range value and then convert that.  */
static struct tm *
ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
		time_t *t, struct tm *tp)
{
  struct tm *r = convert (t, tp);

  if (!r && *t)
    {
      time_t bad = *t;
      time_t ok = 0;

      /* BAD is a known unconvertible time_t, and OK is a known good one.
	 Use binary search to narrow the range between BAD and OK until
	 they differ by 1.  */
      while (bad != ok + (bad < 0 ? -1 : 1))
	{
	  time_t mid = *t = (bad < 0
			     ? bad + ((ok - bad) >> 1)
			     : ok + ((bad - ok) >> 1));
	  r = convert (t, tp);
	  if (r)
	    ok = mid;
	  else
	    bad = mid;
	}

      if (!r && ok)
	{
	  /* The last conversion attempt failed;
	     revert to the most recent successful attempt.  */
	  *t = ok;
	  r = convert (t, tp);
	}
    }

  return r;
}


/* Convert *TP to a time_t value, inverting
   the monotonic and mostly-unit-linear conversion function CONVERT.
   Use *OFFSET to keep track of a guess at the offset of the result,
   compared to what the result would be for UTC without leap seconds.
   If *OFFSET's guess is correct, only one CONVERT call is needed.
   This function is external because it is used also by timegm.c.  */
time_t
__mktime_internal (struct tm *tp,
		   struct tm *(*convert) (const time_t *, struct tm *),
		   time_t *offset)
{
  time_t t, gt, t0, t1, t2;
  struct tm tm;

  /* The maximum number of probes (calls to CONVERT) should be enough
     to handle any combinations of time zone rule changes, solar time,
     leap seconds, and oscillations around a spring-forward gap.
     POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
  int remaining_probes = 6;

  /* Time requested.  Copy it in case CONVERT modifies *TP; this can
     occur if TP is localtime's returned value and CONVERT is localtime.  */
  int sec = tp->tm_sec;
  int min = tp->tm_min;
  int hour = tp->tm_hour;
  int mday = tp->tm_mday;
  int mon = tp->tm_mon;
  int year_requested = tp->tm_year;
  int isdst = tp->tm_isdst;

  /* 1 if the previous probe was DST.  */
  int dst2;

  /* Ensure that mon is in range, and set year accordingly.  */
  int mon_remainder = mon % 12;
  int negative_mon_remainder = mon_remainder < 0;
  int mon_years = mon / 12 - negative_mon_remainder;
  long int lyear_requested = year_requested;
  long int year = lyear_requested + mon_years;

  /* The other values need not be in range:
     the remaining code handles minor overflows correctly,
     assuming int and time_t arithmetic wraps around.
     Major overflows are caught at the end.  */

  /* Calculate day of year from year, month, and day of month.
     The result need not be in range.  */
  int mon_yday = ((__mon_yday[leapyear (year)]
		   [mon_remainder + 12 * negative_mon_remainder])
		  - 1);
  long int lmday = mday;
  long int yday = mon_yday + lmday;

  time_t guessed_offset = *offset;

  int sec_requested = sec;

  if (LEAP_SECONDS_POSSIBLE)
    {
      /* Handle out-of-range seconds specially,
	 since ydhms_tm_diff assumes every minute has 60 seconds.  */
      if (sec < 0)
	sec = 0;
      if (59 < sec)
	sec = 59;
    }