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/* Convert struct partime into time_t.  */

/* Copyright 1992, 1993, 1994, 1995, 1997 Paul Eggert

   Distributed under license by the Free Software Foundation, Inc.

   This file is part of RCS.

   RCS is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 2, or (at your option)

   any later version.

   RCS 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 General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with RCS; see the file COPYING.

   If not, write to the Free Software Foundation,

   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

   Report problems and direct all questions to:

	rcs-bugs@cs.purdue.edu

 */

#if has_conf_h

# include <conf.h>

#else

# if HAVE_CONFIG_H

#  include <config.h>

# else

#  ifndef __STDC__

#   define const

#  endif

# endif

  /* MIPS RISCOS4.52 defines time_t in <sys/types.h> not <time.h>.  */

# include <sys/types.h>

# if HAVE_LIMITS_H

#  include <limits.h>

# endif

# ifndef LONG_MIN

# define LONG_MIN (-1-2147483647L)

# endif

# if STDC_HEADERS

#  include <stdlib.h>

# endif

# include <time.h>

# ifdef __STDC__

#  define P(x) x

# else

#  define P(x) ()

# endif

#endif

#include <partime.h>

#include <maketime.h>

char const maketId[] =

  "$Id: maketime.c,v 5.15 1997/06/17 16:54:36 eggert Exp $";

static int isleap P ((int));

static int month_days P ((struct tm const *));

static time_t maketime P ((struct partime const *, time_t));

/* For maximum portability, use only localtime and gmtime.

   Make no assumptions about the time_t epoch or the range of time_t values.

   Avoid mktime because it's not universal and because there's no easy,

   portable way for mktime to yield the inverse of gmtime.  */

#define TM_YEAR_ORIGIN 1900

static int

isleap (y)

     int y;

{

  return (y & 3) == 0 && (y % 100 != 0 || y % 400 == 0);

}

/* days in year before start of months 0-12 */

static int const month_yday[] =

{

  0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365

};

/* Yield the number of days in TM's month.  */

static int

month_days (tm)

     struct tm const *tm;

{

  int m = tm->tm_mon;

  return (month_yday[m + 1] - month_yday[m]

	  + (m == 1 && isleap (tm->tm_year + TM_YEAR_ORIGIN)));

}

/* Convert UNIXTIME to struct tm form.

   Use gmtime if available and if !LOCALZONE, localtime otherwise.  */

struct tm *

time2tm (unixtime, localzone)

     time_t unixtime;

     int localzone;

{

  struct tm *tm;

#ifdef TZ_is_unset

  static char const *TZ;

  if (!TZ && !(TZ = getenv ("TZ")))

    TZ_is_unset ("The TZ environment variable is not set; please set it to your timezone");

#endif

  if (localzone || !(tm = gmtime (&unixtime)))

    tm = localtime (&unixtime);

  return tm;

}

/* Yield A - B, measured in seconds.  */

time_t

difftm (a, b)

     struct tm const *a;

     struct tm const *b;

{

  int ay = a->tm_year + (TM_YEAR_ORIGIN - 1);

  int by = b->tm_year + (TM_YEAR_ORIGIN - 1);

  int ac = ay / 100 - (ay % 100 < 0);

  int bc = by / 100 - (by % 100 < 0);

  int difference_in_day_of_year = a->tm_yday - b->tm_yday;

  int intervening_leap_days = (((ay >> 2) - (by >> 2))

			       - (ac - bc)

			       + ((ac >> 2) - (bc >> 2)));

  time_t difference_in_years = ay - by;

  time_t difference_in_days

    = (difference_in_years * 365

       + (intervening_leap_days + difference_in_day_of_year));

  return (((((difference_in_days * 24

	      + (a->tm_hour - b->tm_hour))

	     * 60)

	    + (a->tm_min - b->tm_min))

	   * 60)

	  + (a->tm_sec - b->tm_sec));

}

/*

   * Adjust time T by adding SECONDS.  SECONDS must be at most 24 hours' worth.

   * Adjust only T's year, mon, mday, hour, min and sec members;

   * plus adjust wday if it is defined.

 */

void

adjzone (t, seconds)

     register struct tm *t;

     long seconds;

{

  /*

     * This code can be off by a second if SECONDS is not a multiple of 60,

     * if T is local time, and if a leap second happens during this minute.

     * But this bug has never occurred, and most likely will not ever occur.

     * Liberia, the last country for which SECONDS % 60 was nonzero,

     * switched to UTC in May 1972; the first leap second was in June 1972.

   */

  int leap_second = t->tm_sec == 60;

  long sec = seconds + (t->tm_sec - leap_second);

  if (sec < 0)

    {

      if ((t->tm_min -= (59 - sec) / 60) < 0)

	{

	  if ((t->tm_hour -= (59 - t->tm_min) / 60) < 0)

	    {

	      t->tm_hour += 24;

	      if (TM_DEFINED (t->tm_wday) && --t->tm_wday < 0)

		t->tm_wday = 6;

	      if (--t->tm_mday <= 0)

		{

		  if (--t->tm_mon < 0)

		    {

		      --t->tm_year;

		      t->tm_mon = 11;

		    }

		  t->tm_mday = month_days (t);

		}

	    }

	  t->tm_min += 24 * 60;

	}

      sec += 24L * 60 * 60;

    }

  else if (60 <= (t->tm_min += sec / 60))

    if (24 <= (t->tm_hour += t->tm_min / 60))

      {

	t->tm_hour -= 24;

	if (TM_DEFINED (t->tm_wday) && ++t->tm_wday == 7)

	  t->tm_wday = 0;

	if (month_days (t) < ++t->tm_mday)

	  {

	    if (11 < ++t->tm_mon)

	      {

		++t->tm_year;

		t->tm_mon = 0;

	      }

	    t->tm_mday = 1;

	  }

      }

  t->tm_min %= 60;

  t->tm_sec = (int) (sec % 60) + leap_second;

}

/*

   * Convert TM to time_t, using localtime if LOCALZONE and gmtime otherwise.

   * Use only TM's year, mon, mday, hour, min, and sec members.

   * Ignore TM's old tm_yday and tm_wday, but fill in their correct values.

   * Yield -1 on failure (e.g. a member out of range).

   * Posix 1003.1-1990 doesn't allow leap seconds, but some implementations

   * have them anyway, so allow them if localtime/gmtime does.

 */

time_t

tm2time (tm, localzone)

     struct tm *tm;

     int localzone;

{

  /* Cache the most recent t,tm pairs; 1 for gmtime, 1 for localtime.  */

  static time_t t_cache[2];

  static struct tm tm_cache[2];

  time_t d, gt;

  struct tm const *gtm;

  /*

     * The maximum number of iterations should be enough to handle any

     * combinations of leap seconds, time zone rule changes, and solar time.

     * 4 is probably enough; we use a bigger number just to be safe.

   */

  int remaining_tries = 8;

  /* Avoid subscript errors.  */

  if (12 <= (unsigned) tm->tm_mon)

    return -1;

  tm->tm_yday = month_yday[tm->tm_mon] + tm->tm_mday

    - (tm->tm_mon < 2 || !isleap (tm->tm_year + TM_YEAR_ORIGIN));

  /* Make a first guess.  */

  gt = t_cache[localzone];

  gtm = gt ? &tm_cache[localzone] : time2tm (gt, localzone);

  /* Repeatedly use the error from the guess to improve the guess.  */

  while ((d = difftm (tm, gtm)) != 0)

    {

      if (--remaining_tries == 0)

	return -1;

      gt += d;

      gtm = time2tm (gt, localzone);

    }

  /*

     * Check that the guess actually matches;

     * overflow can cause difftm to yield 0 even on differing times,

     * or tm may have members out of range (e.g. bad leap seconds).

   */

#define TM_DIFFER(a,b) \

		( \

			((a)->tm_year ^ (b)->tm_year) | \

			((a)->tm_mon ^ (b)->tm_mon) | \

			((a)->tm_mday ^ (b)->tm_mday) | \

			((a)->tm_hour ^ (b)->tm_hour) | \

			((a)->tm_min ^ (b)->tm_min) | \

			((a)->tm_sec ^ (b)->tm_sec) \

		)

  if (TM_DIFFER (tm, gtm))

    {

      /*

         * If gt is a leap second, try gt+1; if it is one greater than

         * a leap second, try gt-1; otherwise, it doesn't matter.

         * Leap seconds always fall at month end.

       */

      int yd = tm->tm_year - gtm->tm_year;

      gt += yd + (yd ? 0 : tm->tm_mon - gtm->tm_mon);

      gtm = time2tm (gt, localzone);

      if (TM_DIFFER (tm, gtm))

	return -1;

    }

  t_cache[localzone] = gt;

  tm_cache[localzone] = *gtm;

  tm->tm_wday = gtm->tm_wday;

  return gt;

}

/*

   * Check *PT and convert it to time_t.

   * If it is incompletely specified, use DEFAULT_TIME to fill it out.

   * Use localtime if PT->zone is the special value TM_LOCAL_ZONE.

   * Yield -1 on failure.

   * ISO 8601 day-of-year and week numbers are not yet supported.

 */

static time_t

maketime (pt, default_time)

     struct partime const *pt;

     time_t default_time;

{

  int localzone, wday;

  struct tm tm;

  struct tm *tm0 = 0;

  time_t r;

  tm0 = 0;			/* Keep gcc -Wall happy.  */

  localzone = pt->zone == TM_LOCAL_ZONE;

  tm = pt->tm;

  if (TM_DEFINED (pt->ymodulus) || !TM_DEFINED (tm.tm_year))

    {

      /* Get tm corresponding to default time.  */

      tm0 = time2tm (default_time, localzone);

      if (!localzone)

	adjzone (tm0, pt->zone);

    }

  if (TM_DEFINED (pt->ymodulus))

    tm.tm_year +=

      (tm0->tm_year + TM_YEAR_ORIGIN) / pt->ymodulus * pt->ymodulus;

  else if (!TM_DEFINED (tm.tm_year))

    {

      /* Set default year, month, day from current time.  */

      tm.tm_year = tm0->tm_year + TM_YEAR_ORIGIN;

      if (!TM_DEFINED (tm.tm_mon))

	{

	  tm.tm_mon = tm0->tm_mon;

	  if (!TM_DEFINED (tm.tm_mday))

	    tm.tm_mday = tm0->tm_mday;

	}

    }

  /* Convert from partime year (Gregorian) to Posix year.  */

  tm.tm_year -= TM_YEAR_ORIGIN;

  /* Set remaining default fields to be their minimum values.  */

  if (!TM_DEFINED (tm.tm_mon))

    tm.tm_mon = 0;

  if (!TM_DEFINED (tm.tm_mday))

    tm.tm_mday = 1;

  if (!TM_DEFINED (tm.tm_hour))

    tm.tm_hour = 0;

  if (!TM_DEFINED (tm.tm_min))

    tm.tm_min = 0;

  if (!TM_DEFINED (tm.tm_sec))

    tm.tm_sec = 0;

  if (!localzone)

    adjzone (&tm, -pt->zone);

  wday = tm.tm_wday;

  /* Convert and fill in the rest of the tm.  */

  r = tm2time (&tm, localzone);

  /* Check weekday.  */

  if (r != -1 && TM_DEFINED (wday) && wday != tm.tm_wday)

    return -1;

  return r;

}

/* Parse a free-format date in SOURCE, yielding a Unix format time.  */

time_t

str2time (source, default_time, default_zone)

     char const *source;

     time_t default_time;

     long default_zone;

{

  struct partime pt;

  if (*partime (source, &pt))

    return -1;

  if (pt.zone == TM_UNDEFINED_ZONE)

    pt.zone = default_zone;

  return maketime (&pt, default_time);

}

#if TEST

#include <stdio.h>

int

main (argc, argv)

     int argc;

     char **argv;

{

  time_t default_time = time ((time_t *) 0);

  long default_zone = argv[1] ? atol (argv[1]) : 0;

  char buf[1000];

  while (fgets (buf, sizeof (buf), stdin))

    {

      time_t t = str2time (buf, default_time, default_zone);

      printf ("%s", asctime (gmtime (&t)));

    }

  return 0;

}

#endif