Avoid crash on composition (backport from trunk).
[emacs.git] / src / mktime.c
blob20c1092a62a7bbc8911ff864c717e88d7af064b8
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).
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.
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.
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.
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. */
24 /* Define this to have a standalone program to test this implementation of
25 mktime. */
26 /* #define DEBUG 1 */
28 #ifdef HAVE_CONFIG_H
29 # include <config.h>
30 #endif
32 #ifdef _LIBC
33 # define HAVE_LIMITS_H 1
34 # define STDC_HEADERS 1
35 #endif
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
44 #include <sys/types.h> /* Some systems define `time_t' here. */
45 #include <time.h>
47 #if HAVE_LIMITS_H
48 # include <limits.h>
49 #endif
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 */
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. */
68 #ifndef CHAR_BIT
69 # define CHAR_BIT 8
70 #endif
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)))
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
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
94 #define TM_YEAR_BASE 1900
95 #define EPOCH_YEAR 1970
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
104 /* How many days come before each month (0-12). */
105 const unsigned short int __mon_yday[2][13] =
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 }
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;
125 struct tm *l = localtime (t);
126 if (! l)
127 return 0;
128 *tp = *l;
129 return tp;
131 #endif /* ! _LIBC */
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;
145 if (!tp)
146 return 1;
147 else
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));
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;
183 struct tm *r;
185 if (! (r = (*convert) (t, tp)) && *t)
187 time_t bad = *t;
188 time_t ok = 0;
189 struct tm tm;
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))
196 time_t mid = *t = (bad < 0
197 ? bad + ((ok - bad) >> 1)
198 : ok + ((bad - ok) >> 1));
199 if ((r = (*convert) (t, tp)))
201 tm = *r;
202 ok = mid;
204 else
205 bad = mid;
208 if (!r && ok)
210 /* The last conversion attempt failed;
211 revert to the most recent successful attempt. */
212 *t = ok;
213 *tp = tm;
214 r = tp;
218 return r;
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;
237 time_t t, dt, t0, t1, t2;
238 struct tm tm;
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;
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;
256 /* 1 if the previous probe was DST. */
257 int dst2;
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;
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. */
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);
276 int sec_requested = sec;
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;
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
293 /* Invert CONVERT by probing. First assume the same offset as last time.
294 Then repeatedly use the error to improve the guess. */
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);
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;
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)
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;
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;
338 for (i = 1; i <= 3; i++)
340 time_t ot = t - i * quarter;
341 struct tm otm;
342 ranged_convert (convert, &ot, &otm);
343 if (otm.tm_isdst == isdst)
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;
354 *offset = t - t0;
356 #if LEAP_SECONDS_POSSIBLE
357 if (sec_requested != tm.tm_sec)
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;
365 #endif
367 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
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. */
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;
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) */
384 const time_t time_t_max = TIME_T_MAX;
385 const time_t time_t_min = TIME_T_MIN;
387 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
388 return -1;
391 if (year == 69)
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;
399 *tp = tm;
400 return t;
404 static time_t localtime_offset;
406 /* Convert *TP to a time_t value. */
407 time_t
408 mktime (tp)
409 struct tm *tp;
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
418 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
421 #ifdef weak_alias
422 weak_alias (mktime, timelocal)
423 #endif
425 #if DEBUG
427 static int
428 not_equal_tm (a, b)
429 struct tm *a;
430 struct tm *b;
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));
443 static void
444 print_tm (tp)
445 struct tm *tp;
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");
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;
463 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
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;
473 return 0;
477 main (argc, argv)
478 int argc;
479 char **argv;
481 int status = 0;
482 struct tm tm, tmk, tml;
483 struct tm *lt;
484 time_t tk, tl;
485 char trailer;
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))
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)
503 tml = *lt;
504 lt = &tml;
506 printf ("mktime returns %ld == ", (long) tl);
507 print_tm (&tmk);
508 printf ("\n");
509 status = check_result (tl, tmk, tl, lt);
511 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
513 time_t from = atol (argv[1]);
514 time_t by = atol (argv[2]);
515 time_t to = atol (argv[3]);
517 if (argc == 4)
518 for (tl = from; tl <= to; tl += by)
520 lt = localtime (&tl);
521 if (lt)
523 tmk = tml = *lt;
524 tk = mktime (&tmk);
525 status |= check_result (tk, tmk, tl, tml);
527 else
529 printf ("localtime (%ld) yields 0\n", (long) tl);
530 status = 1;
533 else
534 for (tl = from; tl <= to; tl += by)
536 /* Null benchmark. */
537 lt = localtime (&tl);
538 if (lt)
540 tmk = tml = *lt;
541 tk = tl;
542 status |= check_result (tk, tmk, tl, tml);
544 else
546 printf ("localtime (%ld) yields 0\n", (long) tl);
547 status = 1;
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]);
558 return status;
561 #endif /* DEBUG */
564 Local Variables:
565 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
566 End:
569 /* arch-tag: 9456752f-7ddd-47cb-8286-fa807b1355ae
570 (do not change this comment) */