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

  /* Invert CONVERT by probing.  First assume the same offset as last
     time.  */

  t0 = ydhms_diff (year, yday, hour, min, sec,
		   EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, - guessed_offset);

  if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
    {
      /* time_t isn't large enough to rule out overflows, so check
	 for major overflows.  A gross check suffices, since if t0
	 has overflowed, it is off by a multiple of TIME_T_MAX -
	 TIME_T_MIN + 1.  So ignore any component of the difference
	 that is bounded by a small value.  */

      /* Approximate log base 2 of the number of time units per
	 biennium.  A biennium is 2 years; use this unit instead of
	 years to avoid integer overflow.  For example, 2 average
	 Gregorian years are 2 * 365.2425 * 24 * 60 * 60 seconds,
	 which is 63113904 seconds, and rint (log2 (63113904)) is
	 26.  */
      int ALOG2_SECONDS_PER_BIENNIUM = 26;
      int ALOG2_MINUTES_PER_BIENNIUM = 20;
      int ALOG2_HOURS_PER_BIENNIUM = 14;
      int ALOG2_DAYS_PER_BIENNIUM = 10;
      int LOG2_YEARS_PER_BIENNIUM = 1;

      int approx_requested_biennia =
	(SHR (year_requested, LOG2_YEARS_PER_BIENNIUM)
	 - SHR (EPOCH_YEAR - TM_YEAR_BASE, LOG2_YEARS_PER_BIENNIUM)
	 + SHR (mday, ALOG2_DAYS_PER_BIENNIUM)
	 + SHR (hour, ALOG2_HOURS_PER_BIENNIUM)
	 + SHR (min, ALOG2_MINUTES_PER_BIENNIUM)
	 + (LEAP_SECONDS_POSSIBLE
	    ? 0
	    : SHR (sec, ALOG2_SECONDS_PER_BIENNIUM)));

      int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM);
      int diff = approx_biennia - approx_requested_biennia;
      int abs_diff = diff < 0 ? - diff : diff;

      /* IRIX 4.0.5 cc miscaculates TIME_T_MIN / 3: it erroneously
	 gives a positive value of 715827882.  Setting a variable
	 first then doing math on it seems to work.
	 ([e-mail]) */
      time_t time_t_max = TIME_T_MAX;
      time_t time_t_min = TIME_T_MIN;
      time_t overflow_threshold =
	(time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM;

      if (overflow_threshold < abs_diff)
	{
	  /* Overflow occurred.  Try repairing it; this might work if
	     the time zone offset is enough to undo the overflow.  */
	  time_t repaired_t0 = -1 - t0;
	  approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM);
	  diff = approx_biennia - approx_requested_biennia;
	  abs_diff = diff < 0 ? - diff : diff;
	  if (overflow_threshold < abs_diff)
	    return -1;
	  guessed_offset += repaired_t0 - t0;
	  t0 = repaired_t0;
	}
    }

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

  for (t = t1 = t2 = t0, dst2 = 0;
       (gt = guess_time_tm (year, yday, hour, min, sec, &t,
			    ranged_convert (convert, &t, &tm)),
	t != gt);
       t1 = t2, t2 = t, t = gt, dst2 = tm.tm_isdst != 0)
    if (t == t1 && t != t2
	&& (tm.tm_isdst < 0
	    || (isdst < 0
		? dst2 <= (tm.tm_isdst != 0)
		: (isdst != 0) != (tm.tm_isdst != 0))))
      /* We can't possibly find a match, as we are oscillating
	 between two values.  The requested time probably falls
	 within a spring-forward gap of size GT - T.  Follow the common
	 practice in this case, which is to return a time that is GT - T
	 away from the requested time, preferring a time whose
	 tm_isdst differs from the requested value.  (If no tm_isdst
	 was requested and only one of the two values has a nonzero
	 tm_isdst, prefer that value.)  In practice, this is more
	 useful than returning -1.  */
      goto offset_found;
    else if (--remaining_probes == 0)
      return -1;

  /* We have a match.  Check whether tm.tm_isdst has the requested
     value, if any.  */
  if (isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
    {
      /* tm.tm_isdst has the wrong value.  Look for a neighboring
	 time with the right value, and use its UTC offset.

	 Heuristic: probe the adjacent timestamps in both directions,
	 looking for the desired isdst.  This should work for all real
	 time zone histories in the tz database.  */

      /* Distance between probes when looking for a DST boundary.  In
	 tzdata2003a, the shortest period of DST is 601200 seconds
	 (e.g., America/Recife starting 2000-10-08 01:00), and the
	 shortest period of non-DST surrounded by DST is 694800
	 seconds (Africa/Tunis starting 1943-04-17 01:00).  Use the
	 minimum of these two values, so we don't miss these short
	 periods when probing.  */
      int stride = 601200;

      /* The longest period of DST in tzdata2003a is 536454000 seconds
	 (e.g., America/Jujuy starting 1946-10-01 01:00).  The longest
	 period of non-DST is much longer, but it makes no real sense
	 to search for more than a year of non-DST, so use the DST
	 max.  */
      int duration_max = 536454000;

      /* Search in both directions, so the maximum distance is half
	 the duration; add the stride to avoid off-by-1 problems.  */
      int delta_bound = duration_max / 2 + stride;

      int delta, direction;

      for (delta = stride; delta < delta_bound; delta += stride)
	for (direction = -1; direction <= 1; direction += 2)
	  {
	    time_t ot = t + delta * direction;
	    if ((ot < t) == (direction < 0))
	      {
		struct tm otm;
		ranged_convert (convert, &ot, &otm);
		if (otm.tm_isdst == isdst)
		  {
		    /* We found the desired tm_isdst.
		       Extrapolate back to the desired time.  */
		    t = guess_time_tm (year, yday, hour, min, sec, &ot, &otm);
		    ranged_convert (convert, &t, &tm);
		    goto offset_found;
		  }
	      }
	  }
    }

 offset_found:
  *offset = guessed_offset + t - t0;

  if (LEAP_SECONDS_POSSIBLE && sec_requested != tm.tm_sec)
    {
      /* Adjust time to reflect the tm_sec requested, not the normalized value.
	 Also, repair any damage from a false match due to a leap second.  */
      int sec_adjustment = (sec == 0 && tm.tm_sec == 60) - sec;
      t1 = t + sec_requested;
      t2 = t1 + sec_adjustment;
      if (((t1 < t) != (sec_requested < 0))
	  | ((t2 < t1) != (sec_adjustment < 0))
	  | ! convert (&t2, &tm))
	return -1;
      t = t2;
    }

  *tp = tm;
  return t;
}


/* FIXME: This should use a signed type wide enough to hold any UTC
   offset in seconds.  'int' should be good enough for GNU code.  We
   can't fix this unilaterally though, as other modules invoke
   __mktime_internal.  */
static time_t localtime_offset;

/* Convert *TP to a time_t value.  */
time_t
mktime (struct tm *tp)
{
#ifdef _LIBC
  /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
     time zone names contained in the external variable `tzname' shall
     be set as if the tzset() function had been called.  */
  __tzset ();
#endif

  return __mktime_internal (tp, __localtime_r, &localtime_offset);
}

#ifdef weak_alias
weak_alias (mktime, timelocal)
#endif

#ifdef _LIBC
libc_hidden_def (mktime)
libc_hidden_weak (timelocal)
#endif

#if DEBUG

static int
not_equal_tm (const struct tm *a, const struct tm *b)
{
  return ((a->tm_sec ^ b->tm_sec)
	  | (a->tm_min ^ b->tm_min)
	  | (a->tm_hour ^ b->tm_hour)
	  | (a->tm_mday ^ b->tm_mday)
	  | (a->tm_mon ^ b->tm_mon)
	  | (a->tm_year ^ b->tm_year)
	  | (a->tm_yday ^ b->tm_yday)
	  | (a->tm_isdst ^ b->tm_isdst));
}

static void
print_tm (const struct tm *tp)
{
  if (tp)
    printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
	    tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
	    tp->tm_hour, tp->tm_min, tp->tm_sec,
	    tp->tm_yday, tp->tm_wday, tp->tm_isdst);
  else
    printf ("0");
}

static int
check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt)
{
  if (tk != tl || !lt || not_equal_tm (&tmk, lt))
    {
      printf ("mktime (");
      print_tm (lt);
      printf (")\nyields (");
      print_tm (&tmk);
      printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl);
      return 1;
    }

  return 0;
}

int
main (int argc, char **argv)
{
  int status = 0;
  struct tm tm, tmk, tml;
  struct tm *lt;
  time_t tk, tl, tl1;
  char trailer;

  if ((argc == 3 || argc == 4)
      && (sscanf (argv[1], "%d-%d-%d%c",
		  &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
	  == 3)
      && (sscanf (argv[2], "%d:%d:%d%c",
		  &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
	  == 3))
    {
      tm.tm_year -= TM_YEAR_BASE;
      tm.tm_mon--;
      tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
      tmk = tm;
      tl = mktime (&tmk);
      lt = localtime (&tl);
      if (lt)
	{
	  tml = *lt;
	  lt = &tml;
	}
      printf ("mktime returns %ld == ", (long int) tl);
      print_tm (&tmk);
      printf ("\n");
      status = check_result (tl, tmk, tl, lt);
    }
  else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
    {
      time_t from = atol (argv[1]);
      time_t by = atol (argv[2]);
      time_t to = atol (argv[3]);

      if (argc == 4)
	for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
	  {
	    lt = localtime (&tl);
	    if (lt)
	      {
		tmk = tml = *lt;
		tk = mktime (&tmk);
		status |= check_result (tk, tmk, tl, &tml);
	      }
	    else
	      {
		printf ("localtime (%ld) yields 0\n", (long int) tl);
		status = 1;
	      }
	    tl1 = tl + by;
	    if ((tl1 < tl) != (by < 0))
	      break;
	  }
      else
	for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
	  {
	    /* Null benchmark.  */
	    lt = localtime (&tl);
	    if (lt)
	      {
		tmk = tml = *lt;
		tk = tl;
		status |= check_result (tk, tmk, tl, &tml);
	      }
	    else
	      {
		printf ("localtime (%ld) yields 0\n", (long int) tl);
		status = 1;
	      }
	    tl1 = tl + by;
	    if ((tl1 < tl) != (by < 0))
	      break;
	  }
    }
  else
    printf ("Usage:\
\t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
\t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
\t%s FROM BY TO - # Do not test those values (for benchmark).\n",
	    argv[0], argv[0], argv[0]);

  return status;
}

#endif /* DEBUG */

/*
Local Variables:
compile-command: "gcc -DDEBUG -Wall -W -O -g mktime.c -o mktime"
End:
*/