1 /* Convert a `struct tm' to a time_t value.
  2    Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, 2003,
  3                  2004, 2005, 2006, 2007  Free Software Foundation, Inc.
  4    Contributed by Paul Eggert (eggert@twinsun.com).
  5 
  6    NOTE: The canonical source of this file is maintained with the GNU C Library.
  7    Bugs can be reported to bug-glibc@gnu.org.
  8 
  9    This program is free software; you can redistribute it and/or modify it
 10    under the terms of the GNU General Public License as published by the
 11    Free Software Foundation; either version 2, or (at your option) any
 12    later version.
 13 
 14    This program is distributed in the hope that it will be useful,
 15    but WITHOUT ANY WARRANTY; without even the implied warranty of
 16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 17    GNU General Public License for more details.
 18 
 19    You should have received a copy of the GNU General Public License
 20    along with this program; if not, write to the Free Software
 21    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
 22    USA.  */
 23 
 24 /* Define this to have a standalone program to test this implementation of
 25    mktime.  */
 26 /* #define DEBUG 1 */
 27 
 28 #ifdef HAVE_CONFIG_H
 29 # include <config.h>
 30 #endif
 31 
 32 #ifdef _LIBC
 33 # define HAVE_LIMITS_H 1
 34 # define STDC_HEADERS 1
 35 #endif
 36 
 37 /* Assume that leap seconds are possible, unless told otherwise.
 38    If the host has a `zic' command with a `-L leapsecondfilename' option,
 39    then it supports leap seconds; otherwise it probably doesn't.  */
 40 #ifndef LEAP_SECONDS_POSSIBLE
 41 # define LEAP_SECONDS_POSSIBLE 1
 42 #endif
 43 
 44 #include <sys/types.h>          /* Some systems define `time_t' here.  */
 45 #include <time.h>
 46 
 47 #if HAVE_LIMITS_H
 48 # include <limits.h>
 49 #endif
 50 
 51 #if DEBUG
 52 # include <stdio.h>
 53 # if STDC_HEADERS
 54 #  include <stdlib.h>
 55 # endif
 56 /* Make it work even if the system's libc has its own mktime routine.  */
 57 # define mktime my_mktime
 58 #endif /* DEBUG */
 59 
 60 #ifndef __P
 61 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
 62 #  define __P(args) args
 63 # else
 64 #  define __P(args) ()
 65 # endif  /* GCC.  */
 66 #endif  /* Not __P.  */
 67 
 68 #ifndef CHAR_BIT
 69 # define CHAR_BIT 8
 70 #endif
 71 
 72 /* The extra casts work around common compiler bugs.  */
 73 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
 74 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
 75    It is necessary at least when t == time_t.  */
 76 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
 77                               ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
 78 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
 79 
 80 #ifndef INT_MIN
 81 # define INT_MIN TYPE_MINIMUM (int)
 82 #endif
 83 #ifndef INT_MAX
 84 # define INT_MAX TYPE_MAXIMUM (int)
 85 #endif
 86 
 87 #ifndef TIME_T_MIN
 88 # define TIME_T_MIN TYPE_MINIMUM (time_t)
 89 #endif
 90 #ifndef TIME_T_MAX
 91 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
 92 #endif
 93 
 94 #define TM_YEAR_BASE 1900
 95 #define EPOCH_YEAR 1970
 96 
 97 #ifndef __isleap
 98 /* Nonzero if YEAR is a leap year (every 4 years,
 99    except every 100th isn't, and every 400th is).  */
100 # define __isleap(year) \
101   ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
102 #endif
103 
104 /* How many days come before each month (0-12).  */
105 const unsigned short int __mon_yday[2][13] =
106   {
107     /* Normal years.  */
108     { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
109     /* Leap years.  */
110     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
111   };
112 
113 
114 #ifdef _LIBC
115 # define my_mktime_localtime_r __localtime_r
116 #else
117 /* If we're a mktime substitute in a GNU program, then prefer
118    localtime to localtime_r, since many localtime_r implementations
119    are buggy.  */
120 static struct tm *
121 my_mktime_localtime_r (t, tp)
122      const time_t *t;
123      struct tm *tp;
124 {
125   struct tm *l = localtime (t);
126   if (! l)
127     return 0;
128   *tp = *l;
129   return tp;
130 }
131 #endif /* ! _LIBC */
132 
133 
134 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
135    measured in seconds, ignoring leap seconds.
136    YEAR uses the same numbering as TM->tm_year.
137    All values are in range, except possibly YEAR.
138    If TP is null, return a nonzero value.
139    If overflow occurs, yield the low order bits of the correct answer.  */
140 static time_t
141 ydhms_tm_diff (year, yday, hour, min, sec, tp)
142      int year, yday, hour, min, sec;
143      const struct tm *tp;
144 {
145   if (!tp)
146     return 1;
147   else
148     {
149       /* Compute intervening leap days correctly even if year is negative.
150          Take care to avoid int overflow.  time_t overflow is OK, since
151          only the low order bits of the correct time_t answer are needed.
152          Don't convert to time_t until after all divisions are done, since
153          time_t might be unsigned.  */
154       int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
155       int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
156       int a100 = a4 / 25 - (a4 % 25 < 0);
157       int b100 = b4 / 25 - (b4 % 25 < 0);
158       int a400 = a100 >> 2;
159       int b400 = b100 >> 2;
160       int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
161       time_t years = year - (time_t) tp->tm_year;
162       time_t days = (365 * years + intervening_leap_days
163                      + (yday - tp->tm_yday));
164       return (60 * (60 * (24 * days + (hour - tp->tm_hour))
165                     + (min - tp->tm_min))
166               + (sec - tp->tm_sec));
167     }
168 }
169 
170 /* Use CONVERT to convert *T to a broken down time in *TP.
171    If *T is out of range for conversion, adjust it so that
172    it is the nearest in-range value and then convert that.  */
173 static struct tm *
174 ranged_convert (convert, t, tp)
175 #ifdef PROTOTYPES
176      struct tm *(*convert) (const time_t *, struct tm *);
177 #else
178      struct tm *(*convert)();
179 #endif
180      time_t *t;
181      struct tm *tp;
182 {
183   struct tm *r;
184 
185   if (! (r = (*convert) (t, tp)) && *t)
186     {
187       time_t bad = *t;
188       time_t ok = 0;
189       struct tm tm;
190 
191       /* BAD is a known unconvertible time_t, and OK is a known good one.
192          Use binary search to narrow the range between BAD and OK until
193          they differ by 1.  */
194       while (bad != ok + (bad < 0 ? -1 : 1))
195         {
196           time_t mid = *t = (bad < 0
197                              ? bad + ((ok - bad) >> 1)
198                              : ok + ((bad - ok) >> 1));
199           if ((r = (*convert) (t, tp)))
200             {
201               tm = *r;
202               ok = mid;
203             }
204           else
205             bad = mid;
206         }
207 
208       if (!r && ok)
209         {
210           /* The last conversion attempt failed;
211              revert to the most recent successful attempt.  */
212           *t = ok;
213           *tp = tm;
214           r = tp;
215         }
216     }
217 
218   return r;
219 }
220 
221 
222 /* Convert *TP to a time_t value, inverting
223    the monotonic and mostly-unit-linear conversion function CONVERT.
224    Use *OFFSET to keep track of a guess at the offset of the result,
225    compared to what the result would be for UTC without leap seconds.
226    If *OFFSET's guess is correct, only one CONVERT call is needed.  */
227 time_t
228 __mktime_internal (tp, convert, offset)
229      struct tm *tp;
230 #ifdef PROTOTYPES
231      struct tm *(*convert) (const time_t *, struct tm *);
232 #else
233      struct tm *(*convert)();
234 #endif
235      time_t *offset;
236 {
237   time_t t, dt, t0, t1, t2;
238   struct tm tm;
239 
240   /* The maximum number of probes (calls to CONVERT) should be enough
241      to handle any combinations of time zone rule changes, solar time,
242      leap seconds, and oscillations around a spring-forward gap.
243      POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
244   int remaining_probes = 6;
245 
246   /* Time requested.  Copy it in case CONVERT modifies *TP; this can
247      occur if TP is localtime's returned value and CONVERT is localtime.  */
248   int sec = tp->tm_sec;
249   int min = tp->tm_min;
250   int hour = tp->tm_hour;
251   int mday = tp->tm_mday;
252   int mon = tp->tm_mon;
253   int year_requested = tp->tm_year;
254   int isdst = tp->tm_isdst;
255 
256   /* 1 if the previous probe was DST.  */
257   int dst2;
258 
259   /* Ensure that mon is in range, and set year accordingly.  */
260   int mon_remainder = mon % 12;
261   int negative_mon_remainder = mon_remainder < 0;
262   int mon_years = mon / 12 - negative_mon_remainder;
263   int year = year_requested + mon_years;
264 
265   /* The other values need not be in range:
266      the remaining code handles minor overflows correctly,
267      assuming int and time_t arithmetic wraps around.
268      Major overflows are caught at the end.  */
269 
270   /* Calculate day of year from year, month, and day of month.
271      The result need not be in range.  */
272   int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
273                [mon_remainder + 12 * negative_mon_remainder])
274               + mday - 1);
275 
276   int sec_requested = sec;
277 
278   /* Only years after 1970 are defined.
279      If year is 69, it might still be representable due to
280      timezone differences.  */
281   if (year < 69)
282     return -1;
283 
284 #if LEAP_SECONDS_POSSIBLE
285   /* Handle out-of-range seconds specially,
286      since ydhms_tm_diff assumes every minute has 60 seconds.  */
287   if (sec < 0)
288     sec = 0;
289   if (59 < sec)
290     sec = 59;
291 #endif
292 
293   /* Invert CONVERT by probing.  First assume the same offset as last time.
294      Then repeatedly use the error to improve the guess.  */
295 
296   tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
297   tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
298   t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
299 
300   for (t = t1 = t2 = t0 + *offset, dst2 = 0;
301        (dt = ydhms_tm_diff (year, yday, hour, min, sec,
302                             ranged_convert (convert, &t, &tm)));
303        t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
304     if (t == t1 && t != t2
305         && (tm.tm_isdst < 0
306             || (isdst < 0
307                 ? dst2 <= (tm.tm_isdst != 0)
308                 : (isdst != 0) != (tm.tm_isdst != 0))))
309       /* We can't possibly find a match, as we are oscillating
310          between two values.  The requested time probably falls
311          within a spring-forward gap of size DT.  Follow the common
312          practice in this case, which is to return a time that is DT
313          away from the requested time, preferring a time whose
314          tm_isdst differs from the requested value.  (If no tm_isdst
315          was requested and only one of the two values has a nonzero
316          tm_isdst, prefer that value.)  In practice, this is more
317          useful than returning -1.  */
318       break;
319     else if (--remaining_probes == 0)
320       return -1;
321 
322   /* If we have a match, check whether tm.tm_isdst has the requested
323      value, if any.  */
324   if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
325     {
326       /* tm.tm_isdst has the wrong value.  Look for a neighboring
327          time with the right value, and use its UTC offset.
328          Heuristic: probe the previous three calendar quarters (approximately),
329          looking for the desired isdst.  This isn't perfect,
330          but it's good enough in practice.  */
331       int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
332       int i;
333 
334       /* If we're too close to the time_t limit, look in future quarters.  */
335       if (t < TIME_T_MIN + 3 * quarter)
336         quarter = -quarter;
337 
338       for (i = 1; i <= 3; i++)
339         {
340           time_t ot = t - i * quarter;
341           struct tm otm;
342           ranged_convert (convert, &ot, &otm);
343           if (otm.tm_isdst == isdst)
344             {
345               /* We found the desired tm_isdst.
346                  Extrapolate back to the desired time.  */
347               t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
348               ranged_convert (convert, &t, &tm);
349               break;
350             }
351         }
352     }
353 
354   *offset = t - t0;
355 
356 #if LEAP_SECONDS_POSSIBLE
357   if (sec_requested != tm.tm_sec)
358     {
359       /* Adjust time to reflect the tm_sec requested, not the normalized value.
360          Also, repair any damage from a false match due to a leap second.  */
361       t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
362       if (! (*convert) (&t, &tm))
363         return -1;
364     }
365 #endif
366 
367   if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
368     {
369       /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
370          so check for major overflows.  A gross check suffices,
371          since if t has overflowed, it is off by a multiple of
372          TIME_T_MAX - TIME_T_MIN + 1.  So ignore any component of
373          the difference that is bounded by a small value.  */
374 
375       double dyear = (double) year_requested + mon_years - tm.tm_year;
376       double dday = 366 * dyear + mday;
377       double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
378 
379       /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
380          correct results, ie., it erroneously gives a positive value
381          of 715827882.  Setting a variable first then doing math on it
382          seems to work.  (ghazi@caip.rutgers.edu) */
383 
384       const time_t time_t_max = TIME_T_MAX;
385       const time_t time_t_min = TIME_T_MIN;
386 
387       if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
388         return -1;
389     }
390 
391   if (year == 69)
392     {
393       /* If year was 69, need to check whether the time was representable
394          or not.  */
395       if (t < 0 || t > 2 * 24 * 60 * 60)
396         return -1;
397     }
398 
399   *tp = tm;
400   return t;
401 }
402 
403 
404 static time_t localtime_offset;
405 
406 /* Convert *TP to a time_t value.  */
407 time_t
408 mktime (tp)
409      struct tm *tp;
410 {
411 #ifdef _LIBC
412   /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
413      time zone names contained in the external variable `tzname' shall
414      be set as if the tzset() function had been called.  */
415   __tzset ();
416 #endif
417 
418   return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
419 }
420 
421 #ifdef weak_alias
422 weak_alias (mktime, timelocal)
423 #endif
424 
425 #if DEBUG
426 
427 static int
428 not_equal_tm (a, b)
429      struct tm *a;
430      struct tm *b;
431 {
432   return ((a->tm_sec ^ b->tm_sec)
433           | (a->tm_min ^ b->tm_min)
434           | (a->tm_hour ^ b->tm_hour)
435           | (a->tm_mday ^ b->tm_mday)
436           | (a->tm_mon ^ b->tm_mon)
437           | (a->tm_year ^ b->tm_year)
438           | (a->tm_mday ^ b->tm_mday)
439           | (a->tm_yday ^ b->tm_yday)
440           | (a->tm_isdst ^ b->tm_isdst));
441 }
442 
443 static void
444 print_tm (tp)
445      struct tm *tp;
446 {
447   if (tp)
448     printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
449             tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
450             tp->tm_hour, tp->tm_min, tp->tm_sec,
451             tp->tm_yday, tp->tm_wday, tp->tm_isdst);
452   else
453     printf ("0");
454 }
455 
456 static int
457 check_result (tk, tmk, tl, lt)
458      time_t tk;
459      struct tm tmk;
460      time_t tl;
461      struct tm *lt;
462 {
463   if (tk != tl || !lt || not_equal_tm (&tmk, lt))
464     {
465       printf ("mktime (");
466       print_tm (&tmk);
467       printf (")\nyields (");
468       print_tm (lt);
469       printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
470       return 1;
471     }
472 
473   return 0;
474 }
475 
476 int
477 main (argc, argv)
478      int argc;
479      char **argv;
480 {
481   int status = 0;
482   struct tm tm, tmk, tml;
483   struct tm *lt;
484   time_t tk, tl;
485   char trailer;
486 
487   if ((argc == 3 || argc == 4)
488       && (sscanf (argv[1], "%d-%d-%d%c",
489                   &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
490           == 3)
491       && (sscanf (argv[2], "%d:%d:%d%c",
492                   &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
493           == 3))
494     {
495       tm.tm_year -= TM_YEAR_BASE;
496       tm.tm_mon--;
497       tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
498       tmk = tm;
499       tl = mktime (&tmk);
500       lt = localtime (&tl);
501       if (lt)
502         {
503           tml = *lt;
504           lt = &tml;
505         }
506       printf ("mktime returns %ld == ", (long) tl);
507       print_tm (&tmk);
508       printf ("\n");
509       status = check_result (tl, tmk, tl, lt);
510     }
511   else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
512     {
513       time_t from = atol (argv[1]);
514       time_t by = atol (argv[2]);
515       time_t to = atol (argv[3]);
516 
517       if (argc == 4)
518         for (tl = from; tl <= to; tl += by)
519           {
520             lt = localtime (&tl);
521             if (lt)
522               {
523                 tmk = tml = *lt;
524                 tk = mktime (&tmk);
525                 status |= check_result (tk, tmk, tl, tml);
526               }
527             else
528               {
529                 printf ("localtime (%ld) yields 0\n", (long) tl);
530                 status = 1;
531               }
532           }
533       else
534         for (tl = from; tl <= to; tl += by)
535           {
536             /* Null benchmark.  */
537             lt = localtime (&tl);
538             if (lt)
539               {
540                 tmk = tml = *lt;
541                 tk = tl;
542                 status |= check_result (tk, tmk, tl, tml);
543               }
544             else
545               {
546                 printf ("localtime (%ld) yields 0\n", (long) tl);
547                 status = 1;
548               }
549           }
550     }
551   else
552     printf ("Usage:\
553 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
554 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
555 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
556             argv[0], argv[0], argv[0]);
557 
558   return status;
559 }
560 
561 #endif /* DEBUG */
562 
563 /*
564 Local Variables:
565 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
566 End:
567 */
568 
569 /* arch-tag: 9456752f-7ddd-47cb-8286-fa807b1355ae
570    (do not change this comment) */