Fix some boundary cases and remove need for floating point.

[gnulib.git] / lib / mktime.c

/* Convert a `struct tm' to a time_t value.
   Copyright (C) 1993-1999, 2002, 2003 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Paul Eggert (eggert@twinsun.com).

   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, 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.

   You should have received a copy of the GNU General Public License along
   with this program; 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

#ifdef _LIBC
# define STDC_HEADERS 1
#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>

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

/* The extra casts work around common compiler bugs.  */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
   It is necessary at least when t == time_t.  */
#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
                              ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))

#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 (((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, (time_t) 0.5 == 0);
verify (twos_complement_arithmetic, -1 == ~1 + 1);
verify (right_shift_propagates_sign, -1 >> 1 == -1);
/* 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 (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 }
  };


#ifdef _LIBC
# define my_mktime_localtime_r __localtime_r
#else
/* If we're a mktime substitute in a GNU program, then prefer
   localtime to localtime_r, since many localtime_r implementations
   are buggy.  */
static struct tm *
my_mktime_localtime_r (const time_t *t, struct tm *tp)
{
  struct tm *l = localtime (t);
  if (! l)
    return 0;
  *tp = *l;
  return tp;
}
#endif /* ! _LIBC */

/* 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 = (year1 >> 2) + (TM_YEAR_BASE >> 2) - ! (year1 & 3);
  int b4 = (year0 >> 2) + (TM_YEAR_BASE >> 2) - ! (year0 & 3);
  int a100 = a4 / 25 - (a4 % 25 < 0);
  int b100 = b4 / 25 - (b4 % 25 < 0);
  int a400 = a100 >> 2;
  int b400 = 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.  */
  return (*t < TIME_T_MIDPOINT
          ? TIME_T_MIN + (*t == TIME_T_MIN)
          : TIME_T_MAX - (*t == 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;

  if (! (r = (*convert) (t, tp)) && *t)
    {
      time_t bad = *t;
      time_t ok = 0;
      struct tm tm;

      /* 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));
          if ((r = (*convert) (t, tp)))
            {
              tm = *r;
              ok = mid;
            }
          else
            bad = mid;
        }

      if (!r && ok)
        {
          /* The last conversion attempt failed;
             revert to the most recent successful attempt.  */
          *t = ok;
          *tp = tm;
          r = 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.  */
#ifndef _LIBC
static
#endif
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;
    }

  /* 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 =
        ((year_requested >> LOG2_YEARS_PER_BIENNIUM)
         - ((EPOCH_YEAR - TM_YEAR_BASE) >> LOG2_YEARS_PER_BIENNIUM)
         + (mday >> ALOG2_DAYS_PER_BIENNIUM)
         + (hour >> ALOG2_HOURS_PER_BIENNIUM)
         + (min >> ALOG2_MINUTES_PER_BIENNIUM)
         + (LEAP_SECONDS_POSSIBLE ? 0 : sec >> ALOG2_SECONDS_PER_BIENNIUM));

      int approx_biennia = 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.
         (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 = 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) (&t, &tm))
        return -1;
    }

  *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, my_mktime_localtime_r, &localtime_offset);
}

#ifdef weak_alias
weak_alias (mktime, timelocal)
#endif

#ifdef _LIBC
libc_hidden_def (mktime)
libc_hidden_weak (timelocal)
#endif
\f
#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_mday ^ b->tm_mday)
          | (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 */
\f
/*
Local Variables:
compile-command: "gcc -DDEBUG -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
End:
*/