1 /* Convert a `struct tm' to a time_t value.
2 Copyright (C) 1993-1999, 2002-2007, 2009-2011 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Paul Eggert <eggert@twinsun.com>.
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 This program 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
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License along
17 with this program; if not, write to the Free Software Foundation,
18 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
20 /* Define this to have a standalone program to test this implementation of
28 /* Assume that leap seconds are possible, unless told otherwise.
29 If the host has a `zic' command with a `-L leapsecondfilename' option,
30 then it supports leap seconds; otherwise it probably doesn't. */
31 #ifndef LEAP_SECONDS_POSSIBLE
32 # define LEAP_SECONDS_POSSIBLE 1
39 #include <string.h> /* For the real memcpy prototype. */
44 /* Make it work even if the system's libc has its own mktime routine. */
45 # define mktime my_mktime
48 /* Shift A right by B bits portably, by dividing A by 2**B and
49 truncating towards minus infinity. A and B should be free of side
50 effects, and B should be in the range 0 <= B <= INT_BITS - 2, where
51 INT_BITS is the number of useful bits in an int. GNU code can
52 assume that INT_BITS is at least 32.
54 ISO C99 says that A >> B is implementation-defined if A < 0. Some
55 implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift
56 right in the usual way when A < 0, so SHR falls back on division if
57 ordinary A >> B doesn't seem to be the usual signed shift. */
61 : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0))
63 /* The extra casts in the following macros work around compiler bugs,
64 e.g., in Cray C 5.0.3.0. */
66 /* True if the arithmetic type T is an integer type. bool counts as
68 #define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
70 /* True if negative values of the signed integer type T use two's
71 complement, ones' complement, or signed magnitude representation,
72 respectively. Much GNU code assumes two's complement, but some
73 people like to be portable to all possible C hosts. */
74 #define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
75 #define TYPE_ONES_COMPLEMENT(t) ((t) ~ (t) 0 == 0)
76 #define TYPE_SIGNED_MAGNITUDE(t) ((t) ~ (t) 0 < (t) -1)
78 /* True if the arithmetic type T is signed. */
79 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
81 /* The maximum and minimum values for the integer type T. These
82 macros have undefined behavior if T is signed and has padding bits.
83 If this is a problem for you, please let us know how to fix it for
85 #define TYPE_MINIMUM(t) \
86 ((t) (! TYPE_SIGNED (t) \
88 : TYPE_SIGNED_MAGNITUDE (t) \
90 : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
91 #define TYPE_MAXIMUM(t) \
92 ((t) (! TYPE_SIGNED (t) \
94 : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
97 # define TIME_T_MIN TYPE_MINIMUM (time_t)
100 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
102 #define TIME_T_MIDPOINT (SHR (TIME_T_MIN + TIME_T_MAX, 1) + 1)
104 /* Verify a requirement at compile-time (unlike assert, which is runtime). */
105 #define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
107 verify (time_t_is_integer, TYPE_IS_INTEGER (time_t));
108 verify (twos_complement_arithmetic, TYPE_TWOS_COMPLEMENT (int));
109 /* The code also assumes that signed integer overflow silently wraps
110 around, but this assumption can't be stated without causing a
111 diagnostic on some hosts. */
113 #define EPOCH_YEAR 1970
114 #define TM_YEAR_BASE 1900
115 verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);
117 #if INT_MAX <= LONG_MAX / 2
118 typedef long int long_int;
120 typedef long long int long_int;
123 /* Return 1 if YEAR + TM_YEAR_BASE is a leap year. */
125 leapyear (long_int year)
127 /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
128 Also, work even if YEAR is negative. */
132 || ((year / 100) & 3) == (- (TM_YEAR_BASE / 100) & 3)));
135 /* How many days come before each month (0-12). */
139 const unsigned short int __mon_yday[2][13] =
142 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
144 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
149 /* Portable standalone applications should supply a <time.h> that
150 declares a POSIX-compliant localtime_r, for the benefit of older
151 implementations that lack localtime_r or have a nonstandard one.
152 See the gnulib time_r module for one way to implement this. */
153 # undef __localtime_r
154 # define __localtime_r localtime_r
155 # define __mktime_internal mktime_internal
156 # include "mktime-internal.h"
159 /* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
160 (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
161 were not adjusted between the time stamps.
163 The YEAR values uses the same numbering as TP->tm_year. Values
164 need not be in the usual range. However, YEAR1 must not be less
165 than 2 * INT_MIN or greater than 2 * INT_MAX.
167 The result may overflow. It is the caller's responsibility to
171 ydhms_diff (long_int year1, long_int yday1, int hour1, int min1, int sec1,
172 int year0, int yday0, int hour0, int min0, int sec0)
174 verify (C99_integer_division, -1 / 2 == 0);
175 verify (long_int_year_and_yday_are_wide_enough,
176 INT_MAX == INT_MAX * (long_int) 2 / 2);
178 /* Compute intervening leap days correctly even if year is negative.
179 Take care to avoid integer overflow here. */
180 int a4 = SHR (year1, 2) + SHR (TM_YEAR_BASE, 2) - ! (year1 & 3);
181 int b4 = SHR (year0, 2) + SHR (TM_YEAR_BASE, 2) - ! (year0 & 3);
182 int a100 = a4 / 25 - (a4 % 25 < 0);
183 int b100 = b4 / 25 - (b4 % 25 < 0);
184 int a400 = SHR (a100, 2);
185 int b400 = SHR (b100, 2);
186 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
188 /* Compute the desired time in time_t precision. Overflow might
190 time_t tyear1 = year1;
191 time_t years = tyear1 - year0;
192 time_t days = 365 * years + yday1 - yday0 + intervening_leap_days;
193 time_t hours = 24 * days + hour1 - hour0;
194 time_t minutes = 60 * hours + min1 - min0;
195 time_t seconds = 60 * minutes + sec1 - sec0;
200 /* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC),
201 assuming that *T corresponds to *TP and that no clock adjustments
202 occurred between *TP and the desired time.
203 If TP is null, return a value not equal to *T; this avoids false matches.
204 If overflow occurs, yield the minimal or maximal value, except do not
205 yield a value equal to *T. */
207 guess_time_tm (long_int year, long_int yday, int hour, int min, int sec,
208 const time_t *t, const struct tm *tp)
212 time_t d = ydhms_diff (year, yday, hour, min, sec,
213 tp->tm_year, tp->tm_yday,
214 tp->tm_hour, tp->tm_min, tp->tm_sec);
216 if ((t1 < *t) == (TYPE_SIGNED (time_t) ? d < 0 : TIME_T_MAX / 2 < d))
220 /* Overflow occurred one way or another. Return the nearest result
221 that is actually in range, except don't report a zero difference
222 if the actual difference is nonzero, as that would cause a false
223 match; and don't oscillate between two values, as that would
224 confuse the spring-forward gap detector. */
225 return (*t < TIME_T_MIDPOINT
226 ? (*t <= TIME_T_MIN + 1 ? *t + 1 : TIME_T_MIN)
227 : (TIME_T_MAX - 1 <= *t ? *t - 1 : TIME_T_MAX));
230 /* Use CONVERT to convert *T to a broken down time in *TP.
231 If *T is out of range for conversion, adjust it so that
232 it is the nearest in-range value and then convert that. */
234 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
235 time_t *t, struct tm *tp)
237 struct tm *r = convert (t, tp);
244 /* BAD is a known unconvertible time_t, and OK is a known good one.
245 Use binary search to narrow the range between BAD and OK until
247 while (bad != ok + (bad < 0 ? -1 : 1))
249 time_t mid = *t = (bad < 0
250 ? bad + ((ok - bad) >> 1)
251 : ok + ((bad - ok) >> 1));
261 /* The last conversion attempt failed;
262 revert to the most recent successful attempt. */
272 /* Convert *TP to a time_t value, inverting
273 the monotonic and mostly-unit-linear conversion function CONVERT.
274 Use *OFFSET to keep track of a guess at the offset of the result,
275 compared to what the result would be for UTC without leap seconds.
276 If *OFFSET's guess is correct, only one CONVERT call is needed.
277 This function is external because it is used also by timegm.c. */
279 __mktime_internal (struct tm *tp,
280 struct tm *(*convert) (const time_t *, struct tm *),
283 time_t t, gt, t0, t1, t2;
286 /* The maximum number of probes (calls to CONVERT) should be enough
287 to handle any combinations of time zone rule changes, solar time,
288 leap seconds, and oscillations around a spring-forward gap.
289 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
290 int remaining_probes = 6;
292 /* Time requested. Copy it in case CONVERT modifies *TP; this can
293 occur if TP is localtime's returned value and CONVERT is localtime. */
294 int sec = tp->tm_sec;
295 int min = tp->tm_min;
296 int hour = tp->tm_hour;
297 int mday = tp->tm_mday;
298 int mon = tp->tm_mon;
299 int year_requested = tp->tm_year;
300 /* Normalize the value. */
301 int isdst = ((tp->tm_isdst >> (8 * sizeof (tp->tm_isdst) - 1))
302 | (tp->tm_isdst != 0));
304 /* 1 if the previous probe was DST. */
307 /* Ensure that mon is in range, and set year accordingly. */
308 int mon_remainder = mon % 12;
309 int negative_mon_remainder = mon_remainder < 0;
310 int mon_years = mon / 12 - negative_mon_remainder;
311 long_int lyear_requested = year_requested;
312 long_int year = lyear_requested + mon_years;
314 /* The other values need not be in range:
315 the remaining code handles minor overflows correctly,
316 assuming int and time_t arithmetic wraps around.
317 Major overflows are caught at the end. */
319 /* Calculate day of year from year, month, and day of month.
320 The result need not be in range. */
321 int mon_yday = ((__mon_yday[leapyear (year)]
322 [mon_remainder + 12 * negative_mon_remainder])
324 long_int lmday = mday;
325 long_int yday = mon_yday + lmday;
327 time_t guessed_offset = *offset;
329 int sec_requested = sec;
331 if (LEAP_SECONDS_POSSIBLE)
333 /* Handle out-of-range seconds specially,
334 since ydhms_tm_diff assumes every minute has 60 seconds. */
341 /* Invert CONVERT by probing. First assume the same offset as last
344 t0 = ydhms_diff (year, yday, hour, min, sec,
345 EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, - guessed_offset);
347 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
349 /* time_t isn't large enough to rule out overflows, so check
350 for major overflows. A gross check suffices, since if t0
351 has overflowed, it is off by a multiple of TIME_T_MAX -
352 TIME_T_MIN + 1. So ignore any component of the difference
353 that is bounded by a small value. */
355 /* Approximate log base 2 of the number of time units per
356 biennium. A biennium is 2 years; use this unit instead of
357 years to avoid integer overflow. For example, 2 average
358 Gregorian years are 2 * 365.2425 * 24 * 60 * 60 seconds,
359 which is 63113904 seconds, and rint (log2 (63113904)) is
361 int ALOG2_SECONDS_PER_BIENNIUM = 26;
362 int ALOG2_MINUTES_PER_BIENNIUM = 20;
363 int ALOG2_HOURS_PER_BIENNIUM = 14;
364 int ALOG2_DAYS_PER_BIENNIUM = 10;
365 int LOG2_YEARS_PER_BIENNIUM = 1;
367 int approx_requested_biennia =
368 (SHR (year_requested, LOG2_YEARS_PER_BIENNIUM)
369 - SHR (EPOCH_YEAR - TM_YEAR_BASE, LOG2_YEARS_PER_BIENNIUM)
370 + SHR (mday, ALOG2_DAYS_PER_BIENNIUM)
371 + SHR (hour, ALOG2_HOURS_PER_BIENNIUM)
372 + SHR (min, ALOG2_MINUTES_PER_BIENNIUM)
373 + (LEAP_SECONDS_POSSIBLE
375 : SHR (sec, ALOG2_SECONDS_PER_BIENNIUM)));
377 int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM);
378 int diff = approx_biennia - approx_requested_biennia;
379 int abs_diff = diff < 0 ? - diff : diff;
381 /* IRIX 4.0.5 cc miscalculates TIME_T_MIN / 3: it erroneously
382 gives a positive value of 715827882. Setting a variable
383 first then doing math on it seems to work.
384 (ghazi@caip.rutgers.edu) */
385 time_t time_t_max = TIME_T_MAX;
386 time_t time_t_min = TIME_T_MIN;
387 time_t overflow_threshold =
388 (time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM;
390 if (overflow_threshold < abs_diff)
392 /* Overflow occurred. Try repairing it; this might work if
393 the time zone offset is enough to undo the overflow. */
394 time_t repaired_t0 = -1 - t0;
395 approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM);
396 diff = approx_biennia - approx_requested_biennia;
397 abs_diff = diff < 0 ? - diff : diff;
398 if (overflow_threshold < abs_diff)
400 guessed_offset += repaired_t0 - t0;
405 /* Repeatedly use the error to improve the guess. */
407 for (t = t1 = t2 = t0, dst2 = 0;
408 (gt = guess_time_tm (year, yday, hour, min, sec, &t,
409 ranged_convert (convert, &t, &tm)),
411 t1 = t2, t2 = t, t = gt, dst2 = tm.tm_isdst != 0)
412 if (t == t1 && t != t2
415 ? dst2 <= (tm.tm_isdst != 0)
416 : (isdst != 0) != (tm.tm_isdst != 0))))
417 /* We can't possibly find a match, as we are oscillating
418 between two values. The requested time probably falls
419 within a spring-forward gap of size GT - T. Follow the common
420 practice in this case, which is to return a time that is GT - T
421 away from the requested time, preferring a time whose
422 tm_isdst differs from the requested value. (If no tm_isdst
423 was requested and only one of the two values has a nonzero
424 tm_isdst, prefer that value.) In practice, this is more
425 useful than returning -1. */
427 else if (--remaining_probes == 0)
430 /* We have a match. Check whether tm.tm_isdst has the requested
432 if (isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
434 /* tm.tm_isdst has the wrong value. Look for a neighboring
435 time with the right value, and use its UTC offset.
437 Heuristic: probe the adjacent timestamps in both directions,
438 looking for the desired isdst. This should work for all real
439 time zone histories in the tz database. */
441 /* Distance between probes when looking for a DST boundary. In
442 tzdata2003a, the shortest period of DST is 601200 seconds
443 (e.g., America/Recife starting 2000-10-08 01:00), and the
444 shortest period of non-DST surrounded by DST is 694800
445 seconds (Africa/Tunis starting 1943-04-17 01:00). Use the
446 minimum of these two values, so we don't miss these short
447 periods when probing. */
450 /* The longest period of DST in tzdata2003a is 536454000 seconds
451 (e.g., America/Jujuy starting 1946-10-01 01:00). The longest
452 period of non-DST is much longer, but it makes no real sense
453 to search for more than a year of non-DST, so use the DST
455 int duration_max = 536454000;
457 /* Search in both directions, so the maximum distance is half
458 the duration; add the stride to avoid off-by-1 problems. */
459 int delta_bound = duration_max / 2 + stride;
461 int delta, direction;
463 for (delta = stride; delta < delta_bound; delta += stride)
464 for (direction = -1; direction <= 1; direction += 2)
466 time_t ot = t + delta * direction;
467 if ((ot < t) == (direction < 0))
470 ranged_convert (convert, &ot, &otm);
471 if (otm.tm_isdst == isdst)
473 /* We found the desired tm_isdst.
474 Extrapolate back to the desired time. */
475 t = guess_time_tm (year, yday, hour, min, sec, &ot, &otm);
476 ranged_convert (convert, &t, &tm);
484 *offset = guessed_offset + t - t0;
486 if (LEAP_SECONDS_POSSIBLE && sec_requested != tm.tm_sec)
488 /* Adjust time to reflect the tm_sec requested, not the normalized value.
489 Also, repair any damage from a false match due to a leap second. */
490 int sec_adjustment = (sec == 0 && tm.tm_sec == 60) - sec;
491 t1 = t + sec_requested;
492 t2 = t1 + sec_adjustment;
493 if (((t1 < t) != (sec_requested < 0))
494 | ((t2 < t1) != (sec_adjustment < 0))
495 | ! convert (&t2, &tm))
505 /* FIXME: This should use a signed type wide enough to hold any UTC
506 offset in seconds. 'int' should be good enough for GNU code. We
507 can't fix this unilaterally though, as other modules invoke
508 __mktime_internal. */
509 static time_t localtime_offset;
511 /* Convert *TP to a time_t value. */
513 mktime (struct tm *tp)
516 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
517 time zone names contained in the external variable `tzname' shall
518 be set as if the tzset() function had been called. */
522 return __mktime_internal (tp, __localtime_r, &localtime_offset);
526 weak_alias (mktime, timelocal)
530 libc_hidden_def (mktime)
531 libc_hidden_weak (timelocal)
537 not_equal_tm (const struct tm *a, const struct tm *b)
539 return ((a->tm_sec ^ b->tm_sec)
540 | (a->tm_min ^ b->tm_min)
541 | (a->tm_hour ^ b->tm_hour)
542 | (a->tm_mday ^ b->tm_mday)
543 | (a->tm_mon ^ b->tm_mon)
544 | (a->tm_year ^ b->tm_year)
545 | (a->tm_yday ^ b->tm_yday)
546 | (a->tm_isdst ^ b->tm_isdst));
550 print_tm (const struct tm *tp)
553 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
554 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
555 tp->tm_hour, tp->tm_min, tp->tm_sec,
556 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
562 check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt)
564 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
568 printf (")\nyields (");
570 printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl);
578 main (int argc, char **argv)
581 struct tm tm, tmk, tml;
586 if ((argc == 3 || argc == 4)
587 && (sscanf (argv[1], "%d-%d-%d%c",
588 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
590 && (sscanf (argv[2], "%d:%d:%d%c",
591 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
594 tm.tm_year -= TM_YEAR_BASE;
596 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
599 lt = localtime (&tl);
605 printf ("mktime returns %ld == ", (long int) tl);
608 status = check_result (tl, tmk, tl, lt);
610 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
612 time_t from = atol (argv[1]);
613 time_t by = atol (argv[2]);
614 time_t to = atol (argv[3]);
617 for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
619 lt = localtime (&tl);
624 status |= check_result (tk, tmk, tl, &tml);
628 printf ("localtime (%ld) yields 0\n", (long int) tl);
632 if ((tl1 < tl) != (by < 0))
636 for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
638 /* Null benchmark. */
639 lt = localtime (&tl);
644 status |= check_result (tk, tmk, tl, &tml);
648 printf ("localtime (%ld) yields 0\n", (long int) tl);
652 if ((tl1 < tl) != (by < 0))
658 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
659 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
660 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
661 argv[0], argv[0], argv[0]);
670 compile-command: "gcc -DDEBUG -Wall -W -O -g mktime.c -o mktime"