maketime.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

/* 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:

	[e-mail]

 */

#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