nativelibc/time/mktime.c

/*	A part of the Native C Library for Windows NT
	Copyright 2007-2015 PC GO Ld.

	This program 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 of the License, or (at your option) any later version.

	This program 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.
*/

// Based on the GNU C Library

#include <time.h>
#include <string.h>
#include <limits.h>

/* 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))


/* 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]; }

#define EPOCH_YEAR 1970
#define TM_YEAR_BASE 1900

// Accept argument: 0~12
static int month_to_days(unsigned int month) {
	if(month > 12) return -1;
	int r = 0;
	switch(month) {
		case 12:
			r += 31;
		case 11:
			r += 30;
		case 10:
			r += 31;
		case 9:
			r += 30;
		case 8:
			r += 31;
		case 7:
			r += 31;
		case 6:
			r += 30;
		case 5:
			r += 31;
		case 4:
			r += 30;
		case 3:
			r += 31;
		case 2:
			r += 28;
		case 1:
			r += 31;
	}
	return r;
}

/* 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.  */
static 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;
  /* Normalize the value.  */
  int isdst = ((tp->tm_isdst >> (8 * sizeof (tp->tm_isdst) - 1))
	       | (tp->tm_isdst != 0));

  /* 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);
  int mon_yday = (month_to_days(mon_remainder + 12 * negative_mon_remainder) - __isleap(year + TM_YEAR_BASE) ? 0 : 1);
  long int lmday = mday;
  long int yday = mon_yday + lmday;

  time_t guessed_offset = *offset;

  int sec_requested = sec;

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

  /* 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));

      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 miscalculates TIME_T_MIN / 3: it erroneously
	 gives a positive value of 715827882.  Setting a variable
	 first then doing math on it seems to work.
	 (ghazi@caip.rutgers.edu) */
      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 (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) {
  /* 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();

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