1 /* Convert a 'struct tm' to a time_t value.
2 Copyright (C) 1993-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Paul Eggert <eggert@twinsun.com>.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20 /* The following macros influence what gets defined when this file is compiled:
21
22 Macro/expression Which gnulib module This compilation unit
23 should define
24
25 _LIBC (glibc proper) mktime
26
27 NEED_MKTIME_WORKING mktime rpl_mktime
28 || NEED_MKTIME_WINDOWS
29
30 NEED_MKTIME_INTERNAL mktime-internal mktime_internal
31 */
32
33 #ifndef _LIBC
34 # include <libc-config.h>
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 <time.h>
45
46 #include <errno.h>
47 #include <limits.h>
48 #include <stdbool.h>
49 #include <stdlib.h>
50 #include <string.h>
51
52 #include <intprops.h>
53 #include <verify.h>
54
55 #ifndef NEED_MKTIME_INTERNAL
56 # define NEED_MKTIME_INTERNAL 0
57 #endif
58 #ifndef NEED_MKTIME_WINDOWS
59 # define NEED_MKTIME_WINDOWS 0
60 #endif
61 #ifndef NEED_MKTIME_WORKING
62 # define NEED_MKTIME_WORKING 0
63 #endif
64
65 #include "mktime-internal.h"
66
67 #if !defined _LIBC && (NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS)
68 static void
69 my_tzset (void)
70 {
71 # if NEED_MKTIME_WINDOWS
72 /* Rectify the value of the environment variable TZ.
73 There are four possible kinds of such values:
74 - Traditional US time zone names, e.g. "PST8PDT". Syntax: see
75 <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset>
76 - Time zone names based on geography, that contain one or more
77 slashes, e.g. "Europe/Moscow".
78 - Time zone names based on geography, without slashes, e.g.
79 "Singapore".
80 - Time zone names that contain explicit DST rules. Syntax: see
81 <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03>
82 The Microsoft CRT understands only the first kind. It produces incorrect
83 results if the value of TZ is of the other kinds.
84 But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value
85 of the second kind for most geographies, or of the first kind in a few
86 other geographies. If it is of the second kind, neutralize it. For the
87 Microsoft CRT, an absent or empty TZ means the time zone that the user
88 has set in the Windows Control Panel.
89 If the value of TZ is of the third or fourth kind -- Cygwin programs
90 understand these syntaxes as well --, it does not matter whether we
91 neutralize it or not, since these values occur only when a Cygwin user
92 has set TZ explicitly; this case is 1. rare and 2. under the user's
93 responsibility. */
94 const char *tz = getenv ("TZ");
95 if (tz != NULL && strchr (tz, '/') != NULL)
96 _putenv ("TZ=");
97 # else
98 tzset ();
99 # endif
100 }
101 # undef __tzset
102 # define __tzset() my_tzset ()
103 #endif
104
105 #if defined _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_INTERNAL
106
107 /* A signed type that can represent an integer number of years
108 multiplied by four times the number of seconds in a year. It is
109 needed when converting a tm_year value times the number of seconds
110 in a year. The factor of four comes because these products need
111 to be subtracted from each other, and sometimes with an offset
112 added to them, and then with another timestamp added, without
113 worrying about overflow.
114
115 Much of the code uses long_int to represent __time64_t values, to
116 lessen the hassle of dealing with platforms where __time64_t is
117 unsigned, and because long_int should suffice to represent all
118 __time64_t values that mktime can generate even on platforms where
119 __time64_t is wider than the int components of struct tm. */
120
121 #if INT_MAX <= LONG_MAX / 4 / 366 / 24 / 60 / 60
122 typedef long int long_int;
123 #else
124 typedef long long int long_int;
125 #endif
126 verify (INT_MAX <= TYPE_MAXIMUM (long_int) / 4 / 366 / 24 / 60 / 60);
127
128 /* Shift A right by B bits portably, by dividing A by 2**B and
129 truncating towards minus infinity. B should be in the range 0 <= B
130 <= LONG_INT_BITS - 2, where LONG_INT_BITS is the number of useful
131 bits in a long_int. LONG_INT_BITS is at least 32.
132
133 ISO C99 says that A >> B is implementation-defined if A < 0. Some
134 implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift
135 right in the usual way when A < 0, so SHR falls back on division if
136 ordinary A >> B doesn't seem to be the usual signed shift. */
137
138 static long_int
139 shr (long_int a, int b)
140 {
141 long_int one = 1;
142 return (-one >> 1 == -1
143 ? a >> b
144 : (a + (a < 0)) / (one << b) - (a < 0));
145 }
146
147 /* Bounds for the intersection of __time64_t and long_int. */
148
149 static long_int const mktime_min
150 = ((TYPE_SIGNED (__time64_t)
151 && TYPE_MINIMUM (__time64_t) < TYPE_MINIMUM (long_int))
152 ? TYPE_MINIMUM (long_int) : TYPE_MINIMUM (__time64_t));
153 static long_int const mktime_max
154 = (TYPE_MAXIMUM (long_int) < TYPE_MAXIMUM (__time64_t)
155 ? TYPE_MAXIMUM (long_int) : TYPE_MAXIMUM (__time64_t));
156
157 #define EPOCH_YEAR 1970
158 #define TM_YEAR_BASE 1900
159 verify (TM_YEAR_BASE % 100 == 0);
160
161 /* Is YEAR + TM_YEAR_BASE a leap year? */
162 static bool
163 leapyear (long_int year)
164 {
165 /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
166 Also, work even if YEAR is negative. */
167 return
168 ((year & 3) == 0
169 && (year % 100 != 0
170 || ((year / 100) & 3) == (- (TM_YEAR_BASE / 100) & 3)));
171 }
172
173 /* How many days come before each month (0-12). */
174 #ifndef _LIBC
175 static
176 #endif
177 const unsigned short int __mon_yday[2][13] =
178 {
179 /* Normal years. */
180 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
181 /* Leap years. */
182 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
183 };
184
185
186 /* Do the values A and B differ according to the rules for tm_isdst?
187 A and B differ if one is zero and the other positive. */
188 static bool
189 isdst_differ (int a, int b)
190 {
191 return (!a != !b) && (0 <= a) && (0 <= b);
192 }
193
194 /* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
195 (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
196 were not adjusted between the timestamps.
197
198 The YEAR values uses the same numbering as TP->tm_year. Values
199 need not be in the usual range. However, YEAR1 - YEAR0 must not
200 overflow even when multiplied by three times the number of seconds
201 in a year, and likewise for YDAY1 - YDAY0 and three times the
202 number of seconds in a day. */
203
204 static long_int
205 ydhms_diff (long_int year1, long_int yday1, int hour1, int min1, int sec1,
206 int year0, int yday0, int hour0, int min0, int sec0)
207 {
208 verify (-1 / 2 == 0);
209
210 /* Compute intervening leap days correctly even if year is negative.
211 Take care to avoid integer overflow here. */
212 int a4 = shr (year1, 2) + shr (TM_YEAR_BASE, 2) - ! (year1 & 3);
213 int b4 = shr (year0, 2) + shr (TM_YEAR_BASE, 2) - ! (year0 & 3);
214 int a100 = (a4 + (a4 < 0)) / 25 - (a4 < 0);
215 int b100 = (b4 + (b4 < 0)) / 25 - (b4 < 0);
216 int a400 = shr (a100, 2);
217 int b400 = shr (b100, 2);
218 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
219
220 /* Compute the desired time without overflowing. */
221 long_int years = year1 - year0;
222 long_int days = 365 * years + yday1 - yday0 + intervening_leap_days;
223 long_int hours = 24 * days + hour1 - hour0;
224 long_int minutes = 60 * hours + min1 - min0;
225 long_int seconds = 60 * minutes + sec1 - sec0;
226 return seconds;
227 }
228
229 /* Return the average of A and B, even if A + B would overflow.
230 Round toward positive infinity. */
231 static long_int
232 long_int_avg (long_int a, long_int b)
233 {
234 return shr (a, 1) + shr (b, 1) + ((a | b) & 1);
235 }
236
237 /* Return a long_int value corresponding to (YEAR-YDAY HOUR:MIN:SEC)
238 minus *TP seconds, assuming no clock adjustments occurred between
239 the two timestamps.
240
241 YEAR and YDAY must not be so large that multiplying them by three times the
242 number of seconds in a year (or day, respectively) would overflow long_int.
243 *TP should be in the usual range. */
244 static long_int
245 tm_diff (long_int year, long_int yday, int hour, int min, int sec,
246 struct tm const *tp)
247 {
248 return ydhms_diff (year, yday, hour, min, sec,
249 tp->tm_year, tp->tm_yday,
250 tp->tm_hour, tp->tm_min, tp->tm_sec);
251 }
252
253 /* Use CONVERT to convert T to a struct tm value in *TM. T must be in
254 range for __time64_t. Return TM if successful, NULL (setting errno) on
255 failure. */
256 static struct tm *
257 convert_time (struct tm *(*convert) (const __time64_t *, struct tm *),
258 long_int t, struct tm *tm)
259 {
260 __time64_t x = t;
261 return convert (&x, tm);
262 }
263
264 /* Use CONVERT to convert *T to a broken down time in *TP.
265 If *T is out of range for conversion, adjust it so that
266 it is the nearest in-range value and then convert that.
267 A value is in range if it fits in both __time64_t and long_int.
268 Return TP on success, NULL (setting errno) on failure. */
269 static struct tm *
270 ranged_convert (struct tm *(*convert) (const __time64_t *, struct tm *),
271 long_int *t, struct tm *tp)
272 {
273 long_int t1 = (*t < mktime_min ? mktime_min
274 : *t <= mktime_max ? *t : mktime_max);
275 struct tm *r = convert_time (convert, t1, tp);
276 if (r)
277 {
278 *t = t1;
279 return r;
280 }
281 if (errno != EOVERFLOW)
282 return NULL;
283
284 long_int bad = t1;
285 long_int ok = 0;
286 struct tm oktm; oktm.tm_sec = -1;
287
288 /* BAD is a known out-of-range value, and OK is a known in-range one.
289 Use binary search to narrow the range between BAD and OK until
290 they differ by 1. */
291 while (true)
292 {
293 long_int mid = long_int_avg (ok, bad);
294 if (mid == ok || mid == bad)
295 break;
296 if (convert_time (convert, mid, tp))
297 ok = mid, oktm = *tp;
298 else if (errno != EOVERFLOW)
299 return NULL;
300 else
301 bad = mid;
302 }
303
304 if (oktm.tm_sec < 0)
305 return NULL;
306 *t = ok;
307 *tp = oktm;
308 return tp;
309 }
310
311
312 /* Convert *TP to a __time64_t value, inverting
313 the monotonic and mostly-unit-linear conversion function CONVERT.
314 Use *OFFSET to keep track of a guess at the offset of the result,
315 compared to what the result would be for UTC without leap seconds.
316 If *OFFSET's guess is correct, only one CONVERT call is needed.
317 If successful, set *TP to the canonicalized struct tm;
318 otherwise leave *TP alone, return ((time_t) -1) and set errno.
319 This function is external because it is used also by timegm.c. */
320 __time64_t
321 __mktime_internal (struct tm *tp,
322 struct tm *(*convert) (const __time64_t *, struct tm *),
323 mktime_offset_t *offset)
324 {
325 struct tm tm;
326
327 /* The maximum number of probes (calls to CONVERT) should be enough
328 to handle any combinations of time zone rule changes, solar time,
329 leap seconds, and oscillations around a spring-forward gap.
330 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
331 int remaining_probes = 6;
332
333 /* Time requested. Copy it in case CONVERT modifies *TP; this can
334 occur if TP is localtime's returned value and CONVERT is localtime. */
335 int sec = tp->tm_sec;
336 int min = tp->tm_min;
337 int hour = tp->tm_hour;
338 int mday = tp->tm_mday;
339 int mon = tp->tm_mon;
340 int year_requested = tp->tm_year;
341 int isdst = tp->tm_isdst;
342
343 /* 1 if the previous probe was DST. */
344 int dst2 = 0;
345
346 /* Ensure that mon is in range, and set year accordingly. */
347 int mon_remainder = mon % 12;
348 int negative_mon_remainder = mon_remainder < 0;
349 int mon_years = mon / 12 - negative_mon_remainder;
350 long_int lyear_requested = year_requested;
351 long_int year = lyear_requested + mon_years;
352
353 /* The other values need not be in range:
354 the remaining code handles overflows correctly. */
355
356 /* Calculate day of year from year, month, and day of month.
357 The result need not be in range. */
358 int mon_yday = ((__mon_yday[leapyear (year)]
359 [mon_remainder + 12 * negative_mon_remainder])
360 - 1);
361 long_int lmday = mday;
362 long_int yday = mon_yday + lmday;
363
364 mktime_offset_t off = *offset;
365 int negative_offset_guess;
366
367 int sec_requested = sec;
368
369 if (LEAP_SECONDS_POSSIBLE)
370 {
371 /* Handle out-of-range seconds specially,
372 since ydhms_diff assumes every minute has 60 seconds. */
373 if (sec < 0)
374 sec = 0;
375 if (59 < sec)
376 sec = 59;
377 }
378
379 /* Invert CONVERT by probing. First assume the same offset as last
380 time. */
381
382 INT_SUBTRACT_WRAPV (0, off, &negative_offset_guess);
383 long_int t0 = ydhms_diff (year, yday, hour, min, sec,
384 EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0,
385 negative_offset_guess);
386 long_int t = t0, t1 = t0, t2 = t0;
387
388 /* Repeatedly use the error to improve the guess. */
389
390 while (true)
391 {
392 if (! ranged_convert (convert, &t, &tm))
393 return -1;
394 long_int dt = tm_diff (year, yday, hour, min, sec, &tm);
395 if (dt == 0)
396 break;
397
398 if (t == t1 && t != t2
399 && (tm.tm_isdst < 0
400 || (isdst < 0
401 ? dst2 <= (tm.tm_isdst != 0)
402 : (isdst != 0) != (tm.tm_isdst != 0))))
403 /* We can't possibly find a match, as we are oscillating
404 between two values. The requested time probably falls
405 within a spring-forward gap of size DT. Follow the common
406 practice in this case, which is to return a time that is DT
407 away from the requested time, preferring a time whose
408 tm_isdst differs from the requested value. (If no tm_isdst
409 was requested and only one of the two values has a nonzero
410 tm_isdst, prefer that value.) In practice, this is more
411 useful than returning -1. */
412 goto offset_found;
413
414 remaining_probes--;
415 if (remaining_probes == 0)
416 {
417 __set_errno (EOVERFLOW);
418 return -1;
419 }
420
421 t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0;
422 }
423
424 /* We have a match. Check whether tm.tm_isdst has the requested
425 value, if any. */
426 if (isdst_differ (isdst, tm.tm_isdst))
427 {
428 /* tm.tm_isdst has the wrong value. Look for a neighboring
429 time with the right value, and use its UTC offset.
430
431 Heuristic: probe the adjacent timestamps in both directions,
432 looking for the desired isdst. If none is found within a
433 reasonable duration bound, assume a one-hour DST difference.
434 This should work for all real time zone histories in the tz
435 database. */
436
437 /* +1 if we wanted standard time but got DST, -1 if the reverse. */
438 int dst_difference = (isdst == 0) - (tm.tm_isdst == 0);
439
440 /* Distance between probes when looking for a DST boundary. In
441 tzdata2003a, the shortest period of DST is 601200 seconds
442 (e.g., America/Recife starting 2000-10-08 01:00), and the
443 shortest period of non-DST surrounded by DST is 694800
444 seconds (Africa/Tunis starting 1943-04-17 01:00). Use the
445 minimum of these two values, so we don't miss these short
446 periods when probing. */
447 int stride = 601200;
448
449 /* In TZDB 2021e, the longest period of DST (or of non-DST), in
450 which the DST (or adjacent DST) difference is not one hour,
451 is 457243209 seconds: e.g., America/Cambridge_Bay with leap
452 seconds, starting 1965-10-31 00:00 in a switch from
453 double-daylight time (-05) to standard time (-07), and
454 continuing to 1980-04-27 02:00 in a switch from standard time
455 (-07) to daylight time (-06). */
456 int duration_max = 457243209;
457
458 /* Search in both directions, so the maximum distance is half
459 the duration; add the stride to avoid off-by-1 problems. */
460 int delta_bound = duration_max / 2 + stride;
461
462 int delta, direction;
463
464 for (delta = stride; delta < delta_bound; delta += stride)
465 for (direction = -1; direction <= 1; direction += 2)
466 {
467 long_int ot;
468 if (! INT_ADD_WRAPV (t, delta * direction, &ot))
469 {
470 struct tm otm;
471 if (! ranged_convert (convert, &ot, &otm))
472 return -1;
473 if (! isdst_differ (isdst, otm.tm_isdst))
474 {
475 /* We found the desired tm_isdst.
476 Extrapolate back to the desired time. */
477 long_int gt = ot + tm_diff (year, yday, hour, min, sec,
478 &otm);
479 if (mktime_min <= gt && gt <= mktime_max)
480 {
481 if (convert_time (convert, gt, &tm))
482 {
483 t = gt;
484 goto offset_found;
485 }
486 if (errno != EOVERFLOW)
487 return -1;
488 }
489 }
490 }
491 }
492
493 /* No unusual DST offset was found nearby. Assume one-hour DST. */
494 t += 60 * 60 * dst_difference;
495 if (mktime_min <= t && t <= mktime_max && convert_time (convert, t, &tm))
496 goto offset_found;
497
498 __set_errno (EOVERFLOW);
499 return -1;
500 }
501
502 offset_found:
503 /* Set *OFFSET to the low-order bits of T - T0 - NEGATIVE_OFFSET_GUESS.
504 This is just a heuristic to speed up the next mktime call, and
505 correctness is unaffected if integer overflow occurs here. */
506 INT_SUBTRACT_WRAPV (t, t0, offset);
507 INT_SUBTRACT_WRAPV (*offset, negative_offset_guess, offset);
508
509 if (LEAP_SECONDS_POSSIBLE && sec_requested != tm.tm_sec)
510 {
511 /* Adjust time to reflect the tm_sec requested, not the normalized value.
512 Also, repair any damage from a false match due to a leap second. */
513 long_int sec_adjustment = sec == 0 && tm.tm_sec == 60;
514 sec_adjustment -= sec;
515 sec_adjustment += sec_requested;
516 if (INT_ADD_WRAPV (t, sec_adjustment, &t)
517 || ! (mktime_min <= t && t <= mktime_max))
518 {
519 __set_errno (EOVERFLOW);
520 return -1;
521 }
522 if (! convert_time (convert, t, &tm))
523 return -1;
524 }
525
526 *tp = tm;
527 return t;
528 }
529
530 #endif /* _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_INTERNAL */
531
532 #if defined _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS
533
534 /* Convert *TP to a __time64_t value. */
535 __time64_t
536 __mktime64 (struct tm *tp)
537 {
538 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
539 time zone names contained in the external variable 'tzname' shall
540 be set as if the tzset() function had been called. */
541 __tzset ();
542
543 # if defined _LIBC || NEED_MKTIME_WORKING
544 static mktime_offset_t localtime_offset;
545 return __mktime_internal (tp, __localtime64_r, &localtime_offset);
546 # else
547 # undef mktime
548 return mktime (tp);
549 # endif
550 }
551 #endif /* _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS */
552
553 #if defined _LIBC && __TIMESIZE != 64
554
555 libc_hidden_def (__mktime64)
556
557 time_t
558 mktime (struct tm *tp)
559 {
560 struct tm tm = *tp;
561 __time64_t t = __mktime64 (&tm);
562 if (in_time_t_range (t))
563 {
564 *tp = tm;
565 return t;
566 }
567 else
568 {
569 __set_errno (EOVERFLOW);
570 return -1;
571 }
572 }
573
574 #endif
575
576 weak_alias (mktime, timelocal)
577 libc_hidden_def (mktime)
578 libc_hidden_weak (timelocal)