Update to a more recent version of mktime.c.

1 files changed, 498 insertions, 224 deletions

diff --git a/missing_d/mktime.c b/missing_d/mktime.c
index d394ef17..17538a39 100644
--- a/missing_d/mktime.c
+++ b/missing_d/mktime.c
@@ -1,41 +1,50 @@
-/* Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
+/* Convert a 'struct tm' to a time_t value.
+   Copyright (C) 1993-2018 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
-   Contributed by Paul Eggert (eggert@twinsun.com).
+   Contributed by Paul Eggert <eggert@twinsun.com>.
 
    The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Library General Public License as
-   published by the Free Software Foundation; either version 3 of the
-   License, or (at your option) any later version.
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
 
    The GNU C Library 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
-   Library General Public License for more details.
+   Lesser General Public License for more details.
 
-   You should have received a copy of the GNU Library General Public
-   License along with the GNU C Library; see the file COPYING.LIB.  If not,
-   write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
-   Boston, MA 02110-1301, USA.  */
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
 
-/* Define this to have a standalone program to test this implementation of
+/* Define this to 1 to have a standalone program to test this implementation of
    mktime.  */
-/* #define DEBUG 1 */
-
-#ifdef HAVE_CONFIG_H
-#include <config.h>
+#ifndef DEBUG_MKTIME
+# define DEBUG_MKTIME 0
 #endif
 
-#ifdef _LIBC
-# define HAVE_LIMITS_H 1
-# define HAVE_LOCALTIME_R 1
-# define STDC_HEADERS 1
+/* The following macros influence what gets defined when this file is compiled:
+
+   Macro/expression            Which gnulib module    This compilation unit
+                                                      should define
+
+   NEED_MKTIME_WORKING         mktime                 rpl_mktime
+   || NEED_MKTIME_WINDOWS
+
+   NEED_MKTIME_INTERNAL        mktime-internal        mktime_internal
+
+   DEBUG_MKTIME                (defined manually)     my_mktime, main
+ */
+
+#if !defined _LIBC && !DEBUG_MKTIME
+# include <config.h>
 #endif
 
 /* Assume that leap seconds are possible, unless told otherwise.
-   If the host has a `zic' command with a `-L leapsecondfilename' option,
+   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
+# define LEAP_SECONDS_POSSIBLE 1
 #endif
 
 #ifndef VMS
@@ -48,54 +57,99 @@
 #if HAVE_LIMITS_H
 #include <limits.h>
 #endif
-
-#if DEBUG
-#include <stdio.h>
-#if STDC_HEADERS
-#include <stdlib.h>
+#if HAVE_STDBOOL_H
+#include <stdbool.h>
 #endif
-/* Make it work even if the system's libc has its own mktime routine.  */
-#define mktime my_mktime
-#endif /* DEBUG */
 
-#ifndef __P
-#if defined (__GNUC__) || (defined (__STDC__) && __STDC__)
-#define __P(args) args
-#else
-#define __P(args) ()
-#endif  /* GCC.  */
-#endif  /* Not __P.  */
+#include <intprops.h>
+#include <verify.h>
 
-#ifndef CHAR_BIT
-#define CHAR_BIT 8
+#if DEBUG_MKTIME
+# include <stdio.h>
+# include <stdlib.h>
+# include <string.h>
+/* Make it work even if the system's libc has its own mktime routine.  */
+# undef mktime
+# define mktime my_mktime
 #endif
 
-#ifndef INT_MIN
-#define INT_MIN (~0 << (sizeof (int) * CHAR_BIT - 1))
-#endif
-#ifndef INT_MAX
-#define INT_MAX (~0 - INT_MIN)
+#if NEED_MKTIME_WINDOWS /* on native Windows */
+# include <stdlib.h>
+# include <string.h>
 #endif
 
-#ifndef TIME_T_MIN
-#define TIME_T_MIN (0 < (time_t) -1 ? (time_t) 0 \
-		    : ~ (time_t) 0 << (sizeof (time_t) * CHAR_BIT - 1))
-#endif
-#ifndef TIME_T_MAX
-#define TIME_T_MAX (~ (time_t) 0 - TIME_T_MIN)
+#if NEED_MKTIME_WORKING || NEED_MKTIME_INTERNAL || DEBUG_MKTIME
+
+/* A signed type that can represent an integer number of years
+   multiplied by three times the number of seconds in a year.  It is
+   needed when converting a tm_year value times the number of seconds
+   in a year.  The factor of three comes because these products need
+   to be subtracted from each other, and sometimes with an offset
+   added to them, without worrying about overflow.
+
+   Much of the code uses long_int to represent time_t values, to
+   lessen the hassle of dealing with platforms where time_t is
+   unsigned, and because long_int should suffice to represent all
+   time_t values that mktime can generate even on platforms where
+   time_t is excessively wide.  */
+
+#if INT_MAX <= LONG_MAX / 3 / 366 / 24 / 60 / 60
+typedef long int long_int;
+#else
+typedef long long int long_int;
 #endif
+verify (INT_MAX <= TYPE_MAXIMUM (long_int) / 3 / 366 / 24 / 60 / 60);
+
+/* Shift A right by B bits portably, by dividing A by 2**B and
+   truncating towards minus infinity.  B should be in the range 0 <= B
+   <= LONG_INT_BITS - 2, where LONG_INT_BITS is the number of useful
+   bits in a long_int.  LONG_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.  */
+
+static long_int
+shr (long_int a, int b)
+{
+  long_int one = 1;
+  return (-one >> 1 == -1
+	  ? a >> b
+	  : a / (one << b) - (a % (one << b) < 0));
+}
+
+/* Bounds for the intersection of time_t and long_int.  */
+
+static long_int const mktime_min
+  = ((TYPE_SIGNED (time_t) && TYPE_MINIMUM (time_t) < TYPE_MINIMUM (long_int))
+     ? TYPE_MINIMUM (long_int) : TYPE_MINIMUM (time_t));
+static long_int const mktime_max
+  = (TYPE_MAXIMUM (long_int) < TYPE_MAXIMUM (time_t)
+     ? TYPE_MAXIMUM (long_int) : TYPE_MAXIMUM (time_t));
+
+verify (TYPE_IS_INTEGER (time_t));
 
-#define TM_YEAR_BASE 1900
 #define EPOCH_YEAR 1970
+#define TM_YEAR_BASE 1900
+verify (TM_YEAR_BASE % 100 == 0);
 
-#ifndef __isleap
-/* Nonzero if YEAR is a leap year (every 4 years,
-   except every 100th isn't, and every 400th is).  */
-#define	__isleap(year)	\
-  ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
-#endif
+/* Is YEAR + TM_YEAR_BASE a leap year?  */
+static bool
+leapyear (long_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.  */
@@ -104,93 +158,180 @@ const unsigned short int __mon_yday[2][13] =
     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
   };
 
-static time_t ydhms_tm_diff __P ((int, int, int, int, int, const struct tm *));
-time_t __mktime_internal __P ((struct tm *,
-			       struct tm *(*) (const time_t *, struct tm *),
-			       time_t *));
 
+#ifdef _LIBC
+typedef time_t mktime_offset_t;
+#else
+/* Portable standalone applications should supply a <time.h> that
+   declares a POSIX-compliant localtime_r, for the benefit of older
+   implementations that lack localtime_r or have a nonstandard one.
+   See the gnulib time_r module for one way to implement this.  */
+# undef __localtime_r
+# define __localtime_r localtime_r
+# define __mktime_internal mktime_internal
+# include "mktime-internal.h"
+#endif
 
-static struct tm *my_localtime_r __P ((const time_t *, struct tm *));
-static struct tm *
-my_localtime_r (t, tp)
-     const time_t *t;
-     struct tm *tp;
+/* Do the values A and B differ according to the rules for tm_isdst?
+   A and B differ if one is zero and the other positive.  */
+static bool
+isdst_differ (int a, int b)
 {
-  struct tm *l = localtime (t);
-  if (! l)
-    return 0;
-  *tp = *l;
-  return tp;
+  return (!a != !b) && (0 <= a) && (0 <= b);
 }
 
+/* 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 timestamps.
+
+   The YEAR values uses the same numbering as TP->tm_year.  Values
+   need not be in the usual range.  However, YEAR1 must not overflow
+   when multiplied by three times the number of seconds in a year, and
+   likewise for YDAY1 and three times the number of seconds in a day.  */
 
-/* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
-   measured in seconds, ignoring leap seconds.
-   YEAR uses the same numbering as TM->tm_year.
-   All values are in range, except possibly YEAR.
-   If overflow occurs, yield the low order bits of the correct answer.  */
-static time_t
-ydhms_tm_diff (year, yday, hour, min, sec, tp)
-     int year, yday, hour, min, sec;
-     const struct tm *tp;
+static long_int
+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 (-1 / 2 == 0);
+
   /* Compute intervening leap days correctly even if year is negative.
-     Take care to avoid int overflow.  time_t overflow is OK, since
-     only the low order bits of the correct time_t answer are needed.
-     Don't convert to time_t until after all divisions are done, since
-     time_t might be unsigned.  */
-  int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
-  int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
+     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 = a100 >> 2;
-  int b400 = b100 >> 2;
+  int a400 = shr (a100, 2);
+  int b400 = shr (b100, 2);
   int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
-  time_t years = year - (time_t) tp->tm_year;
-  time_t days = (365 * years + intervening_leap_days
-		 + (yday - tp->tm_yday));
-  return (60 * (60 * (24 * days + (hour - tp->tm_hour))
-		+ (min - tp->tm_min))
-	  + (sec - tp->tm_sec));
+
+  /* Compute the desired time without overflowing.  */
+  long_int years = year1 - year0;
+  long_int days = 365 * years + yday1 - yday0 + intervening_leap_days;
+  long_int hours = 24 * days + hour1 - hour0;
+  long_int minutes = 60 * hours + min1 - min0;
+  long_int seconds = 60 * minutes + sec1 - sec0;
+  return seconds;
+}
+
+/* Return the average of A and B, even if A + B would overflow.
+   Round toward positive infinity.  */
+static long_int
+long_int_avg (long_int a, long_int b)
+{
+  return shr (a, 1) + shr (b, 1) + ((a | b) & 1);
 }
 
+/* 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.
+   Although T and the returned value are of type long_int,
+   they represent time_t values and must be in time_t range.
+   If TP is null, return a value not equal to T; this avoids false matches.
+   YEAR and YDAY must not be so large that multiplying them by three times the
+   number of seconds in a year (or day, respectively) would overflow long_int.
+   If the returned value would be out of range, yield the minimal or
+   maximal in-range value, except do not yield a value equal to T.  */
+static long_int
+guess_time_tm (long_int year, long_int yday, int hour, int min, int sec,
+	       long_int t, const struct tm *tp)
+{
+  if (tp)
+    {
+      long_int result;
+      long_int d = ydhms_diff (year, yday, hour, min, sec,
+			       tp->tm_year, tp->tm_yday,
+			       tp->tm_hour, tp->tm_min, tp->tm_sec);
+      if (! INT_ADD_WRAPV (t, d, &result))
+	return result;
+    }
 
-static time_t localtime_offset;
+  /* 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 < long_int_avg (mktime_min, mktime_max)
+	  ? (t <= mktime_min + 1 ? t + 1 : mktime_min)
+	  : (mktime_max - 1 <= t ? t - 1 : mktime_max));
+}
 
-/* Convert *TP to a time_t value.  */
-time_t
-mktime (tp)
-     struct tm *tp;
+/* Use CONVERT to convert T to a struct tm value in *TM.  T must be in
+   range for time_t.  Return TM if successful, NULL if T is out of
+   range for CONVERT.  */
+static struct tm *
+convert_time (struct tm *(*convert) (const time_t *, struct tm *),
+	      long_int t, struct tm *tm)
 {
-#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
+  time_t x = t;
+  return convert (&x, tm);
+}
+
+/* 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.
+   A value is in range if it fits in both time_t and long_int.  */
+static struct tm *
+ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
+		long_int *t, struct tm *tp)
+{
+  struct tm *r;
+  if (*t < mktime_min)
+    *t = mktime_min;
+  else if (mktime_max < *t)
+    *t = mktime_max;
+  r = convert_time (convert, *t, tp);
+
+  if (!r && *t)
+    {
+      long_int bad = *t;
+      long_int ok = 0;
+
+      /* BAD is a known unconvertible value, and OK is a known good one.
+	 Use binary search to narrow the range between BAD and OK until
+	 they differ by 1.  */
+      while (true)
+	{
+	  long_int mid = long_int_avg (ok, bad);
+	  if (mid != ok && mid != bad)
+	    break;
+	  r = convert_time (convert, mid, tp);
+	  if (r)
+	    ok = mid;
+	  else
+	    bad = mid;
+	}
+
+      if (!r && ok)
+	{
+	  /* The last conversion attempt failed;
+	     revert to the most recent successful attempt.  */
+	  r = convert_time (convert, ok, tp);
+	}
+    }
 
-  return __mktime_internal (tp, my_localtime_r, &localtime_offset);
+  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.  */
+   If *OFFSET's guess is correct, only one CONVERT call is needed.
+   This function is external because it is used also by timegm.c.  */
 time_t
-__mktime_internal (tp, convert, offset)
-     struct tm *tp;
-     struct tm *(*convert) __P ((const time_t *, struct tm *));
-     time_t *offset;
+__mktime_internal (struct tm *tp,
+		   struct tm *(*convert) (const time_t *, struct tm *),
+		   mktime_offset_t *offset)
 {
-  time_t t, dt, t0;
+  long_int t, gt, t0, t1, t2, dt;
   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,
-     and leap seconds.  Posix.1 prohibits leap seconds, but some hosts
-     have them anyway.  */
-  int remaining_probes = 4;
+     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.  */
@@ -202,98 +343,143 @@ __mktime_internal (tp, convert, offset)
   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;
-  int year = year_requested + mon_years;
+  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.  */
+     the remaining code handles overflows correctly.  */
 
   /* Calculate day of year from year, month, and day of month.
      The result need not be in range.  */
-  int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
-	       [mon_remainder + 12 * negative_mon_remainder])
-	      + mday - 1);
+  int mon_yday = ((__mon_yday[leapyear (year)]
+		   [mon_remainder + 12 * negative_mon_remainder])
+		  - 1);
+  long_int lmday = mday;
+  long_int yday = mon_yday + lmday;
 
-#if LEAP_SECONDS_POSSIBLE
-  /* Handle out-of-range seconds specially,
-     since ydhms_tm_diff assumes every minute has 60 seconds.  */
-  int sec_requested = sec;
-  if (sec < 0)
-    sec = 0;
-  if (59 < sec)
-    sec = 59;
-#endif
+  int negative_offset_guess;
 
-  /* Invert CONVERT by probing.  First assume the same offset as last time.
-     Then repeatedly use the error to improve the guess.  */
+  int sec_requested = sec;
 
-  tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
-  tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
-  t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
+  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;
+    }
 
-  for (t = t0 + *offset;
-       (dt = ydhms_tm_diff (year, yday, hour, min, sec, (*convert) (&t, &tm)));
-       t += dt)
-    if (--remaining_probes == 0)
+  /* Invert CONVERT by probing.  First assume the same offset as last
+     time.  */
+
+  INT_SUBTRACT_WRAPV (0, *offset, &negative_offset_guess);
+  t0 = ydhms_diff (year, yday, hour, min, sec,
+		   EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, negative_offset_guess);
+
+  /* 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;
 
-  /* Check whether tm.tm_isdst has the requested value, if any.  */
-  if (0 <= isdst && 0 <= tm.tm_isdst)
+  /* We have a match.  Check whether tm.tm_isdst has the requested
+     value, if any.  */
+  if (isdst_differ (isdst, tm.tm_isdst))
     {
-      int dst_diff = (isdst != 0) - (tm.tm_isdst != 0);
-      if (dst_diff)
-	{
-	  /* Move two hours in the direction indicated by the disagreement,
-	     probe some more, and switch to a new time if found.
-	     The largest known fallback due to daylight savings is two hours:
-	     once, in Newfoundland, 1988-10-30 02:00 -> 00:00.  */
-	  time_t ot = t - 2 * 60 * 60 * dst_diff;
-	  while (--remaining_probes != 0)
-	    {
-	      struct tm otm;
-	      if (! (dt = ydhms_tm_diff (year, yday, hour, min, sec,
-					 (*convert) (&ot, &otm))))
-		{
-		  t = ot;
-		  tm = otm;
-		  break;
-		}
-	      if ((ot += dt) == t)
-		break;  /* Avoid a redundant probe.  */
-	    }
-	}
+      /* 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)
+	  {
+	    long_int ot;
+	    if (! INT_ADD_WRAPV (t, delta * direction, &ot))
+	      {
+		struct tm otm;
+		ranged_convert (convert, &ot, &otm);
+		if (! isdst_differ (isdst, otm.tm_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 = t - t0;
+ offset_found:
+  /* Set *OFFSET to the low-order bits of T - T0 - NEGATIVE_OFFSET_GUESS.
+     This is just a heuristic to speed up the next mktime call, and
+     correctness is unaffected if integer overflow occurs here.  */
+  INT_SUBTRACT_WRAPV (t, t0, &dt);
+  INT_SUBTRACT_WRAPV (dt, negative_offset_guess, offset);
 
-#if LEAP_SECONDS_POSSIBLE
-  if (sec_requested != tm.tm_sec)
+  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.  */
-      t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
-      (*convert) (&t, &tm);
-    }
-#endif
-
-  if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
-    {
-      /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
-	 so check for major overflows.  A gross check suffices,
-	 since if t 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.  */
-
-      double dyear = (double) year_requested + mon_years - tm.tm_year;
-      double dday = 366 * dyear + mday;
-      double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
-
-      if (TIME_T_MAX / 3 - TIME_T_MIN / 3 < (dsec < 0 ? - dsec : dsec))
+      long_int sec_adjustment = sec == 0 && tm.tm_sec == 60;
+      sec_adjustment -= sec;
+      sec_adjustment += sec_requested;
+      if (INT_ADD_WRAPV (t, sec_adjustment, &t)
+	  || ! (mktime_min <= t && t <= mktime_max)
+	  || ! convert_time (convert, t, &tm))
 	return -1;
     }
 
@@ -301,16 +487,78 @@ __mktime_internal (tp, convert, offset)
   return t;
 }
 
+#endif /* NEED_MKTIME_WORKING || NEED_MKTIME_INTERNAL || DEBUG_MKTIME */
+
+#if NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS || DEBUG_MKTIME
+
+# if NEED_MKTIME_WORKING || DEBUG_MKTIME
+static mktime_offset_t localtime_offset;
+# endif
+
+/* Convert *TP to a time_t value.  */
+time_t
+mktime (struct tm *tp)
+{
+# if NEED_MKTIME_WINDOWS
+  /* Rectify the value of the environment variable TZ.
+     There are four possible kinds of such values:
+       - Traditional US time zone names, e.g. "PST8PDT".  Syntax: see
+         <https://msdn.microsoft.com/en-us/library/90s5c885.aspx>
+       - Time zone names based on geography, that contain one or more
+         slashes, e.g. "Europe/Moscow".
+       - Time zone names based on geography, without slashes, e.g.
+         "Singapore".
+       - Time zone names that contain explicit DST rules.  Syntax: see
+         <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03>
+     The Microsoft CRT understands only the first kind.  It produces incorrect
+     results if the value of TZ is of the other kinds.
+     But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value
+     of the second kind for most geographies, or of the first kind in a few
+     other geographies.  If it is of the second kind, neutralize it.  For the
+     Microsoft CRT, an absent or empty TZ means the time zone that the user
+     has set in the Windows Control Panel.
+     If the value of TZ is of the third or fourth kind -- Cygwin programs
+     understand these syntaxes as well --, it does not matter whether we
+     neutralize it or not, since these values occur only when a Cygwin user
+     has set TZ explicitly; this case is 1. rare and 2. under the user's
+     responsibility.  */
+  const char *tz = getenv ("TZ");
+  if (tz != NULL && strchr (tz, '/') != NULL)
+    _putenv ("TZ=");
+# endif
+
+# if NEED_MKTIME_WORKING || DEBUG_MKTIME
+#  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 ();
+#  elif HAVE_TZSET
+  tzset ();
+#  endif
+
+  return __mktime_internal (tp, __localtime_r, &localtime_offset);
+# else
+#  undef mktime
+  return mktime (tp);
+# endif
+}
+
+#endif /* NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS || DEBUG_MKTIME */
+
 #ifdef weak_alias
 weak_alias (mktime, timelocal)
 #endif
+
+#ifdef _LIBC
+libc_hidden_def (mktime)
+libc_hidden_weak (timelocal)
+#endif
 
-#if DEBUG
+#if DEBUG_MKTIME
 
 static int
-not_equal_tm (a, b)
-     struct tm *a;
-     struct tm *b;
+not_equal_tm (const struct tm *a, const struct tm *b)
 {
   return ((a->tm_sec ^ b->tm_sec)
 	  | (a->tm_min ^ b->tm_min)
@@ -318,35 +566,32 @@ not_equal_tm (a, b)
 	  | (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));
+	  | isdst_differ (a->tm_isdst, b->tm_isdst));
 }
 
 static void
-print_tm (tp)
-     struct tm *tp;
+print_tm (const struct tm *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);
+  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 (tk, tmk, tl, tml)
-     time_t tk;
-     struct tm tmk;
-     time_t tl;
-     struct tm tml;
+check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt)
 {
-  if (tk != tl || not_equal_tm (&tmk, &tml))
+  if (tk != tl || !lt || not_equal_tm (&tmk, lt))
     {
       printf ("mktime (");
-      print_tm (&tmk);
+      print_tm (lt);
       printf (")\nyields (");
-      print_tm (&tml);
-      printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
+      print_tm (&tmk);
+      printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl);
       return 1;
     }
 
@@ -354,15 +599,22 @@ check_result (tk, tmk, tl, tml)
 }
 
 int
-main (argc, argv)
-     int argc;
-     char **argv;
+main (int argc, char **argv)
 {
   int status = 0;
   struct tm tm, tmk, tml;
-  time_t tk, tl;
+  struct tm *lt;
+  time_t tk, tl, tl1;
   char trailer;
 
+  /* Sanity check, plus call tzset.  */
+  tl = 0;
+  if (! localtime (&tl))
+    {
+      printf ("localtime (0) fails\n");
+      status = 1;
+    }
+
   if ((argc == 3 || argc == 4)
       && (sscanf (argv[1], "%d-%d-%d%c",
 		  &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
@@ -376,11 +628,11 @@ main (argc, argv)
       tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
       tmk = tm;
       tl = mktime (&tmk);
-      tml = *localtime (&tl);
-      printf ("mktime returns %ld == ", (long) tl);
+      lt = localtime_r (&tl, &tml);
+      printf ("mktime returns %ld == ", (long int) tl);
       print_tm (&tmk);
       printf ("\n");
-      status = check_result (tl, tmk, tl, tml);
+      status = check_result (tl, tmk, tl, lt);
     }
   else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
     {
@@ -389,21 +641,43 @@ main (argc, argv)
       time_t to = atol (argv[3]);
 
       if (argc == 4)
-	for (tl = from; tl <= to; tl += by)
+	for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
 	  {
-	    tml = *localtime (&tl);
-	    tmk = tml;
-	    tk = mktime (&tmk);
-	    status |= check_result (tk, tmk, tl, tml);
+	    lt = localtime_r (&tl, &tml);
+	    if (lt)
+	      {
+		tmk = tml;
+		tk = mktime (&tmk);
+		status |= check_result (tk, tmk, tl, &tml);
+	      }
+	    else
+	      {
+		printf ("localtime_r (%ld) yields 0\n", (long int) tl);
+		status = 1;
+	      }
+	    tl1 = tl + by;
+	    if ((tl1 < tl) != (by < 0))
+	      break;
 	  }
       else
-	for (tl = from; tl <= to; tl += by)
+	for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
 	  {
 	    /* Null benchmark.  */
-	    tml = *localtime (&tl);
-	    tmk = tml;
-	    tk = tl;
-	    status |= check_result (tk, tmk, tl, tml);
+	    lt = localtime_r (&tl, &tml);
+	    if (lt)
+	      {
+		tmk = tml;
+		tk = tl;
+		status |= check_result (tk, tmk, tl, &tml);
+	      }
+	    else
+	      {
+		printf ("localtime_r (%ld) yields 0\n", (long int) tl);
+		status = 1;
+	      }
+	    tl1 = tl + by;
+	    if ((tl1 < tl) != (by < 0))
+	      break;
 	  }
     }
   else
@@ -416,10 +690,10 @@ main (argc, argv)
   return status;
 }
 
-#endif /* DEBUG */
+#endif /* DEBUG_MKTIME */
 
 /*
 Local Variables:
-compile-command: "gcc -DDEBUG=1 -Wall -O -g mktime.c -o mktime"
+compile-command: "gcc -DDEBUG_MKTIME -I. -Wall -W -O2 -g mktime.c -o mktime"
 End:
 */