1 /* Convert a `struct tm' to a time_t value.
2 Copyright (C) 1993-1999, 2002, 2003, 2004, 2005 Free Software Foundation,
4 This file is part of the GNU C Library.
5 Contributed by Paul Eggert (eggert@twinsun.com).
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2, or (at your option)
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License along
18 with this program; if not, write to the Free Software Foundation,
19 Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
21 /* Define this to have a standalone program to test this implementation of
29 /* Assume that leap seconds are possible, unless told otherwise.
30 If the host has a `zic' command with a `-L leapsecondfilename' option,
31 then it supports leap seconds; otherwise it probably doesn't. */
32 #ifndef LEAP_SECONDS_POSSIBLE
33 # define LEAP_SECONDS_POSSIBLE 1
36 #include <sys/types.h> /* Some systems define `time_t' here. */
45 /* Make it work even if the system's libc has its own mktime routine. */
46 # define mktime my_mktime
49 /* Shift A right by B bits portably, by dividing A by 2**B and
50 truncating towards minus infinity. A and B should be free of side
51 effects, and B should be in the range 0 <= B <= INT_BITS - 2, where
52 INT_BITS is the number of useful bits in an int. GNU code can
53 assume that INT_BITS is at least 32.
55 ISO C99 says that A >> B is implementation-defined if A < 0. Some
56 implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift
57 right in the usual way when A < 0, so SHR falls back on division if
58 ordinary A >> B doesn't seem to be the usual signed shift. */
62 : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0))
64 /* The extra casts in the following macros work around compiler bugs,
65 e.g., in Cray C 5.0.3.0. */
67 /* True if the arithmetic type T is an integer type. bool counts as
69 #define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
71 /* True if negative values of the integer type T use twos complement
73 #define TYPE_TWOS_COMPLEMENT(t) ((t) - (t) 1 == (t) ((t) ~ (t) 1 + (t) 1))
75 /* True if the arithmetic type T is signed. */
76 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
78 /* The maximum and minimum values for the integer type T. These
79 macros have undefined behavior if T is signed and has padding bits
80 (i.e., bits that do not contribute to the value), or if T uses
81 signed-magnitude representation. If this is a problem for you,
82 please let us know how to fix it for your host. */
83 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
84 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
85 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
88 # define TIME_T_MIN TYPE_MINIMUM (time_t)
91 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
93 #define TIME_T_MIDPOINT (SHR (TIME_T_MIN + TIME_T_MAX, 1) + 1)
95 /* Verify a requirement at compile-time (unlike assert, which is runtime). */
96 #define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
98 verify (time_t_is_integer, TYPE_IS_INTEGER (time_t));
99 verify (twos_complement_arithmetic, TYPE_TWOS_COMPLEMENT (int));
100 /* The code also assumes that signed integer overflow silently wraps
101 around, but this assumption can't be stated without causing a
102 diagnostic on some hosts. */
104 #define EPOCH_YEAR 1970
105 #define TM_YEAR_BASE 1900
106 verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);
108 /* Return 1 if YEAR + TM_YEAR_BASE is a leap year. */
110 leapyear (long int year)
112 /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
113 Also, work even if YEAR is negative. */
117 || ((year / 100) & 3) == (- (TM_YEAR_BASE / 100) & 3)));
120 /* How many days come before each month (0-12). */
124 const unsigned short int __mon_yday[2][13] =
127 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
129 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
134 /* Portable standalone applications should supply a "time_r.h" that
135 declares a POSIX-compliant localtime_r, for the benefit of older
136 implementations that lack localtime_r or have a nonstandard one.
137 See the gnulib time_r module for one way to implement this. */
139 # undef __localtime_r
140 # define __localtime_r localtime_r
141 # define __mktime_internal mktime_internal
144 /* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
145 (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
146 were not adjusted between the time stamps.
148 The YEAR values uses the same numbering as TP->tm_year. Values
149 need not be in the usual range. However, YEAR1 must not be less
150 than 2 * INT_MIN or greater than 2 * INT_MAX.
152 The result may overflow. It is the caller's responsibility to
156 ydhms_diff (long int year1, long int yday1, int hour1, int min1, int sec1,
157 int year0, int yday0, int hour0, int min0, int sec0)
159 verify (C99_integer_division, -1 / 2 == 0);
160 verify (long_int_year_and_yday_are_wide_enough,
161 INT_MAX <= LONG_MAX / 2 || TIME_T_MAX <= UINT_MAX);
163 /* Compute intervening leap days correctly even if year is negative.
164 Take care to avoid integer overflow here. */
165 int a4 = SHR (year1, 2) + SHR (TM_YEAR_BASE, 2) - ! (year1 & 3);
166 int b4 = SHR (year0, 2) + SHR (TM_YEAR_BASE, 2) - ! (year0 & 3);
167 int a100 = a4 / 25 - (a4 % 25 < 0);
168 int b100 = b4 / 25 - (b4 % 25 < 0);
169 int a400 = SHR (a100, 2);
170 int b400 = SHR (b100, 2);
171 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
173 /* Compute the desired time in time_t precision. Overflow might
175 time_t tyear1 = year1;
176 time_t years = tyear1 - year0;
177 time_t days = 365 * years + yday1 - yday0 + intervening_leap_days;
178 time_t hours = 24 * days + hour1 - hour0;
179 time_t minutes = 60 * hours + min1 - min0;
180 time_t seconds = 60 * minutes + sec1 - sec0;
185 /* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC),
186 assuming that *T corresponds to *TP and that no clock adjustments
187 occurred between *TP and the desired time.
188 If TP is null, return a value not equal to *T; this avoids false matches.
189 If overflow occurs, yield the minimal or maximal value, except do not
190 yield a value equal to *T. */
192 guess_time_tm (long int year, long int yday, int hour, int min, int sec,
193 const time_t *t, const struct tm *tp)
197 time_t d = ydhms_diff (year, yday, hour, min, sec,
198 tp->tm_year, tp->tm_yday,
199 tp->tm_hour, tp->tm_min, tp->tm_sec);
201 if ((t1 < *t) == (TYPE_SIGNED (time_t) ? d < 0 : TIME_T_MAX / 2 < d))
205 /* Overflow occurred one way or another. Return the nearest result
206 that is actually in range, except don't report a zero difference
207 if the actual difference is nonzero, as that would cause a false
209 return (*t < TIME_T_MIDPOINT
210 ? TIME_T_MIN + (*t == TIME_T_MIN)
211 : TIME_T_MAX - (*t == TIME_T_MAX));
214 /* Use CONVERT to convert *T to a broken down time in *TP.
215 If *T is out of range for conversion, adjust it so that
216 it is the nearest in-range value and then convert that. */
218 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
219 time_t *t, struct tm *tp)
223 if (! (r = (*convert) (t, tp)) && *t)
229 /* BAD is a known unconvertible time_t, and OK is a known good one.
230 Use binary search to narrow the range between BAD and OK until
232 while (bad != ok + (bad < 0 ? -1 : 1))
234 time_t mid = *t = (bad < 0
235 ? bad + ((ok - bad) >> 1)
236 : ok + ((bad - ok) >> 1));
237 if ((r = (*convert) (t, tp)))
248 /* The last conversion attempt failed;
249 revert to the most recent successful attempt. */
260 /* Convert *TP to a time_t value, inverting
261 the monotonic and mostly-unit-linear conversion function CONVERT.
262 Use *OFFSET to keep track of a guess at the offset of the result,
263 compared to what the result would be for UTC without leap seconds.
264 If *OFFSET's guess is correct, only one CONVERT call is needed.
265 This function is external because it is used also by timegm.c. */
267 __mktime_internal (struct tm *tp,
268 struct tm *(*convert) (const time_t *, struct tm *),
271 time_t t, gt, t0, t1, t2;
274 /* The maximum number of probes (calls to CONVERT) should be enough
275 to handle any combinations of time zone rule changes, solar time,
276 leap seconds, and oscillations around a spring-forward gap.
277 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
278 int remaining_probes = 6;
280 /* Time requested. Copy it in case CONVERT modifies *TP; this can
281 occur if TP is localtime's returned value and CONVERT is localtime. */
282 int sec = tp->tm_sec;
283 int min = tp->tm_min;
284 int hour = tp->tm_hour;
285 int mday = tp->tm_mday;
286 int mon = tp->tm_mon;
287 int year_requested = tp->tm_year;
288 int isdst = tp->tm_isdst;
290 /* 1 if the previous probe was DST. */
293 /* Ensure that mon is in range, and set year accordingly. */
294 int mon_remainder = mon % 12;
295 int negative_mon_remainder = mon_remainder < 0;
296 int mon_years = mon / 12 - negative_mon_remainder;
297 long int lyear_requested = year_requested;
298 long int year = lyear_requested + mon_years;
300 /* The other values need not be in range:
301 the remaining code handles minor overflows correctly,
302 assuming int and time_t arithmetic wraps around.
303 Major overflows are caught at the end. */
305 /* Calculate day of year from year, month, and day of month.
306 The result need not be in range. */
307 int mon_yday = ((__mon_yday[leapyear (year)]
308 [mon_remainder + 12 * negative_mon_remainder])
310 long int lmday = mday;
311 long int yday = mon_yday + lmday;
313 time_t guessed_offset = *offset;
315 int sec_requested = sec;
317 if (LEAP_SECONDS_POSSIBLE)
319 /* Handle out-of-range seconds specially,
320 since ydhms_tm_diff assumes every minute has 60 seconds. */
327 /* Invert CONVERT by probing. First assume the same offset as last
330 t0 = ydhms_diff (year, yday, hour, min, sec,
331 EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, - guessed_offset);
333 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
335 /* time_t isn't large enough to rule out overflows, so check
336 for major overflows. A gross check suffices, since if t0
337 has overflowed, it is off by a multiple of TIME_T_MAX -
338 TIME_T_MIN + 1. So ignore any component of the difference
339 that is bounded by a small value. */
341 /* Approximate log base 2 of the number of time units per
342 biennium. A biennium is 2 years; use this unit instead of
343 years to avoid integer overflow. For example, 2 average
344 Gregorian years are 2 * 365.2425 * 24 * 60 * 60 seconds,
345 which is 63113904 seconds, and rint (log2 (63113904)) is
347 int ALOG2_SECONDS_PER_BIENNIUM = 26;
348 int ALOG2_MINUTES_PER_BIENNIUM = 20;
349 int ALOG2_HOURS_PER_BIENNIUM = 14;
350 int ALOG2_DAYS_PER_BIENNIUM = 10;
351 int LOG2_YEARS_PER_BIENNIUM = 1;
353 int approx_requested_biennia =
354 (SHR (year_requested, LOG2_YEARS_PER_BIENNIUM)
355 - SHR (EPOCH_YEAR - TM_YEAR_BASE, LOG2_YEARS_PER_BIENNIUM)
356 + SHR (mday, ALOG2_DAYS_PER_BIENNIUM)
357 + SHR (hour, ALOG2_HOURS_PER_BIENNIUM)
358 + SHR (min, ALOG2_MINUTES_PER_BIENNIUM)
359 + (LEAP_SECONDS_POSSIBLE
361 : SHR (sec, ALOG2_SECONDS_PER_BIENNIUM)));
363 int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM);
364 int diff = approx_biennia - approx_requested_biennia;
365 int abs_diff = diff < 0 ? - diff : diff;
367 /* IRIX 4.0.5 cc miscaculates TIME_T_MIN / 3: it erroneously
368 gives a positive value of 715827882. Setting a variable
369 first then doing math on it seems to work.
370 (ghazi@caip.rutgers.edu) */
371 time_t time_t_max = TIME_T_MAX;
372 time_t time_t_min = TIME_T_MIN;
373 time_t overflow_threshold =
374 (time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM;
376 if (overflow_threshold < abs_diff)
378 /* Overflow occurred. Try repairing it; this might work if
379 the time zone offset is enough to undo the overflow. */
380 time_t repaired_t0 = -1 - t0;
381 approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM);
382 diff = approx_biennia - approx_requested_biennia;
383 abs_diff = diff < 0 ? - diff : diff;
384 if (overflow_threshold < abs_diff)
386 guessed_offset += repaired_t0 - t0;
391 /* Repeatedly use the error to improve the guess. */
393 for (t = t1 = t2 = t0, dst2 = 0;
394 (gt = guess_time_tm (year, yday, hour, min, sec, &t,
395 ranged_convert (convert, &t, &tm)),
397 t1 = t2, t2 = t, t = gt, dst2 = tm.tm_isdst != 0)
398 if (t == t1 && t != t2
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 GT - T. Follow the common
406 practice in this case, which is to return a time that is GT - T
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. */
413 else if (--remaining_probes == 0)
416 /* We have a match. Check whether tm.tm_isdst has the requested
418 if (isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
420 /* tm.tm_isdst has the wrong value. Look for a neighboring
421 time with the right value, and use its UTC offset.
423 Heuristic: probe the adjacent timestamps in both directions,
424 looking for the desired isdst. This should work for all real
425 time zone histories in the tz database. */
427 /* Distance between probes when looking for a DST boundary. In
428 tzdata2003a, the shortest period of DST is 601200 seconds
429 (e.g., America/Recife starting 2000-10-08 01:00), and the
430 shortest period of non-DST surrounded by DST is 694800
431 seconds (Africa/Tunis starting 1943-04-17 01:00). Use the
432 minimum of these two values, so we don't miss these short
433 periods when probing. */
436 /* The longest period of DST in tzdata2003a is 536454000 seconds
437 (e.g., America/Jujuy starting 1946-10-01 01:00). The longest
438 period of non-DST is much longer, but it makes no real sense
439 to search for more than a year of non-DST, so use the DST
441 int duration_max = 536454000;
443 /* Search in both directions, so the maximum distance is half
444 the duration; add the stride to avoid off-by-1 problems. */
445 int delta_bound = duration_max / 2 + stride;
447 int delta, direction;
449 for (delta = stride; delta < delta_bound; delta += stride)
450 for (direction = -1; direction <= 1; direction += 2)
452 time_t ot = t + delta * direction;
453 if ((ot < t) == (direction < 0))
456 ranged_convert (convert, &ot, &otm);
457 if (otm.tm_isdst == isdst)
459 /* We found the desired tm_isdst.
460 Extrapolate back to the desired time. */
461 t = guess_time_tm (year, yday, hour, min, sec, &ot, &otm);
462 ranged_convert (convert, &t, &tm);
470 *offset = guessed_offset + t - t0;
472 if (LEAP_SECONDS_POSSIBLE && sec_requested != tm.tm_sec)
474 /* Adjust time to reflect the tm_sec requested, not the normalized value.
475 Also, repair any damage from a false match due to a leap second. */
476 int sec_adjustment = (sec == 0 && tm.tm_sec == 60) - sec;
477 t1 = t + sec_requested;
478 t2 = t1 + sec_adjustment;
479 if (((t1 < t) != (sec_requested < 0))
480 | ((t2 < t1) != (sec_adjustment < 0))
481 | ! (*convert) (&t2, &tm))
491 /* FIXME: This should use a signed type wide enough to hold any UTC
492 offset in seconds. 'int' should be good enough for GNU code. We
493 can't fix this unilaterally though, as other modules invoke
494 __mktime_internal. */
495 static time_t localtime_offset;
497 /* Convert *TP to a time_t value. */
499 mktime (struct tm *tp)
502 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
503 time zone names contained in the external variable `tzname' shall
504 be set as if the tzset() function had been called. */
508 return __mktime_internal (tp, __localtime_r, &localtime_offset);
512 weak_alias (mktime, timelocal)
516 libc_hidden_def (mktime)
517 libc_hidden_weak (timelocal)
523 not_equal_tm (const struct tm *a, const struct tm *b)
525 return ((a->tm_sec ^ b->tm_sec)
526 | (a->tm_min ^ b->tm_min)
527 | (a->tm_hour ^ b->tm_hour)
528 | (a->tm_mday ^ b->tm_mday)
529 | (a->tm_mon ^ b->tm_mon)
530 | (a->tm_year ^ b->tm_year)
531 | (a->tm_yday ^ b->tm_yday)
532 | (a->tm_isdst ^ b->tm_isdst));
536 print_tm (const struct tm *tp)
539 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
540 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
541 tp->tm_hour, tp->tm_min, tp->tm_sec,
542 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
548 check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt)
550 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
554 printf (")\nyields (");
556 printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl);
564 main (int argc, char **argv)
567 struct tm tm, tmk, tml;
572 if ((argc == 3 || argc == 4)
573 && (sscanf (argv[1], "%d-%d-%d%c",
574 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
576 && (sscanf (argv[2], "%d:%d:%d%c",
577 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
580 tm.tm_year -= TM_YEAR_BASE;
582 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
585 lt = localtime (&tl);
591 printf ("mktime returns %ld == ", (long int) tl);
594 status = check_result (tl, tmk, tl, lt);
596 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
598 time_t from = atol (argv[1]);
599 time_t by = atol (argv[2]);
600 time_t to = atol (argv[3]);
603 for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
605 lt = localtime (&tl);
610 status |= check_result (tk, tmk, tl, &tml);
614 printf ("localtime (%ld) yields 0\n", (long int) tl);
618 if ((tl1 < tl) != (by < 0))
622 for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
624 /* Null benchmark. */
625 lt = localtime (&tl);
630 status |= check_result (tk, tmk, tl, &tml);
634 printf ("localtime (%ld) yields 0\n", (long int) tl);
638 if ((tl1 < tl) != (by < 0))
644 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
645 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
646 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
647 argv[0], argv[0], argv[0]);
656 compile-command: "gcc -DDEBUG -Wall -W -O -g mktime.c -o mktime"