1 /* Convert a `struct tm' to a time_t value.
2 Copyright (C) 1993-1999, 2002, 2003, 2004 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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
35 #include <sys/types.h> /* Some systems define `time_t' here. */
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 work around common compiler bugs. */
64 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
65 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
66 It is necessary at least when t == time_t. */
67 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
68 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
69 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
72 # define TIME_T_MIN TYPE_MINIMUM (time_t)
75 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
77 #define TIME_T_MIDPOINT (SHR (TIME_T_MIN + TIME_T_MAX, 1) + 1)
79 /* Verify a requirement at compile-time (unlike assert, which is runtime). */
80 #define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
82 verify (time_t_is_integer, (time_t) 0.5 == 0);
83 verify (twos_complement_arithmetic, -1 == ~1 + 1);
84 /* The code also assumes that signed integer overflow silently wraps
85 around, but this assumption can't be stated without causing a
86 diagnostic on some hosts. */
88 #define EPOCH_YEAR 1970
89 #define TM_YEAR_BASE 1900
90 verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);
92 /* Return 1 if YEAR + TM_YEAR_BASE is a leap year. */
94 leapyear (long int year)
96 /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
97 Also, work even if YEAR is negative. */
101 || ((year / 100) & 3) == (- (TM_YEAR_BASE / 100) & 3)));
104 /* How many days come before each month (0-12). */
108 const unsigned short int __mon_yday[2][13] =
111 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
113 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
118 /* Portable standalone applications should supply a "time_r.h" that
119 declares a POSIX-compliant localtime_r, for the benefit of older
120 implementations that lack localtime_r or have a nonstandard one.
121 See the gnulib time_r module for one way to implement this. */
123 # undef __localtime_r
124 # define __localtime_r localtime_r
125 # define __mktime_internal mktime_internal
128 /* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
129 (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
130 were not adjusted between the time stamps.
132 The YEAR values uses the same numbering as TP->tm_year. Values
133 need not be in the usual range. However, YEAR1 must not be less
134 than 2 * INT_MIN or greater than 2 * INT_MAX.
136 The result may overflow. It is the caller's responsibility to
140 ydhms_diff (long int year1, long int yday1, int hour1, int min1, int sec1,
141 int year0, int yday0, int hour0, int min0, int sec0)
143 verify (C99_integer_division, -1 / 2 == 0);
144 verify (long_int_year_and_yday_are_wide_enough,
145 INT_MAX <= LONG_MAX / 2 || TIME_T_MAX <= UINT_MAX);
147 /* Compute intervening leap days correctly even if year is negative.
148 Take care to avoid integer overflow here. */
149 int a4 = SHR (year1, 2) + SHR (TM_YEAR_BASE, 2) - ! (year1 & 3);
150 int b4 = SHR (year0, 2) + SHR (TM_YEAR_BASE, 2) - ! (year0 & 3);
151 int a100 = a4 / 25 - (a4 % 25 < 0);
152 int b100 = b4 / 25 - (b4 % 25 < 0);
153 int a400 = SHR (a100, 2);
154 int b400 = SHR (b100, 2);
155 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
157 /* Compute the desired time in time_t precision. Overflow might
159 time_t tyear1 = year1;
160 time_t years = tyear1 - year0;
161 time_t days = 365 * years + yday1 - yday0 + intervening_leap_days;
162 time_t hours = 24 * days + hour1 - hour0;
163 time_t minutes = 60 * hours + min1 - min0;
164 time_t seconds = 60 * minutes + sec1 - sec0;
169 /* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC),
170 assuming that *T corresponds to *TP and that no clock adjustments
171 occurred between *TP and the desired time.
172 If TP is null, return a value not equal to *T; this avoids false matches.
173 If overflow occurs, yield the minimal or maximal value, except do not
174 yield a value equal to *T. */
176 guess_time_tm (long int year, long int yday, int hour, int min, int sec,
177 const time_t *t, const struct tm *tp)
181 time_t d = ydhms_diff (year, yday, hour, min, sec,
182 tp->tm_year, tp->tm_yday,
183 tp->tm_hour, tp->tm_min, tp->tm_sec);
185 if ((t1 < *t) == (TYPE_SIGNED (time_t) ? d < 0 : TIME_T_MAX / 2 < d))
189 /* Overflow occurred one way or another. Return the nearest result
190 that is actually in range, except don't report a zero difference
191 if the actual difference is nonzero, as that would cause a false
193 return (*t < TIME_T_MIDPOINT
194 ? TIME_T_MIN + (*t == TIME_T_MIN)
195 : TIME_T_MAX - (*t == TIME_T_MAX));
198 /* Use CONVERT to convert *T to a broken down time in *TP.
199 If *T is out of range for conversion, adjust it so that
200 it is the nearest in-range value and then convert that. */
202 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
203 time_t *t, struct tm *tp)
207 if (! (r = (*convert) (t, tp)) && *t)
213 /* BAD is a known unconvertible time_t, and OK is a known good one.
214 Use binary search to narrow the range between BAD and OK until
216 while (bad != ok + (bad < 0 ? -1 : 1))
218 time_t mid = *t = (bad < 0
219 ? bad + ((ok - bad) >> 1)
220 : ok + ((bad - ok) >> 1));
221 if ((r = (*convert) (t, tp)))
232 /* The last conversion attempt failed;
233 revert to the most recent successful attempt. */
244 /* Convert *TP to a time_t value, inverting
245 the monotonic and mostly-unit-linear conversion function CONVERT.
246 Use *OFFSET to keep track of a guess at the offset of the result,
247 compared to what the result would be for UTC without leap seconds.
248 If *OFFSET's guess is correct, only one CONVERT call is needed.
249 This function is external because it is used also by timegm.c. */
251 __mktime_internal (struct tm *tp,
252 struct tm *(*convert) (const time_t *, struct tm *),
255 time_t t, gt, t0, t1, t2;
258 /* The maximum number of probes (calls to CONVERT) should be enough
259 to handle any combinations of time zone rule changes, solar time,
260 leap seconds, and oscillations around a spring-forward gap.
261 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
262 int remaining_probes = 6;
264 /* Time requested. Copy it in case CONVERT modifies *TP; this can
265 occur if TP is localtime's returned value and CONVERT is localtime. */
266 int sec = tp->tm_sec;
267 int min = tp->tm_min;
268 int hour = tp->tm_hour;
269 int mday = tp->tm_mday;
270 int mon = tp->tm_mon;
271 int year_requested = tp->tm_year;
272 int isdst = tp->tm_isdst;
274 /* 1 if the previous probe was DST. */
277 /* Ensure that mon is in range, and set year accordingly. */
278 int mon_remainder = mon % 12;
279 int negative_mon_remainder = mon_remainder < 0;
280 int mon_years = mon / 12 - negative_mon_remainder;
281 long int lyear_requested = year_requested;
282 long int year = lyear_requested + mon_years;
284 /* The other values need not be in range:
285 the remaining code handles minor overflows correctly,
286 assuming int and time_t arithmetic wraps around.
287 Major overflows are caught at the end. */
289 /* Calculate day of year from year, month, and day of month.
290 The result need not be in range. */
291 int mon_yday = ((__mon_yday[leapyear (year)]
292 [mon_remainder + 12 * negative_mon_remainder])
294 long int lmday = mday;
295 long int yday = mon_yday + lmday;
297 time_t guessed_offset = *offset;
299 int sec_requested = sec;
301 if (LEAP_SECONDS_POSSIBLE)
303 /* Handle out-of-range seconds specially,
304 since ydhms_tm_diff assumes every minute has 60 seconds. */
311 /* Invert CONVERT by probing. First assume the same offset as last
314 t0 = ydhms_diff (year, yday, hour, min, sec,
315 EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, - guessed_offset);
317 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
319 /* time_t isn't large enough to rule out overflows, so check
320 for major overflows. A gross check suffices, since if t0
321 has overflowed, it is off by a multiple of TIME_T_MAX -
322 TIME_T_MIN + 1. So ignore any component of the difference
323 that is bounded by a small value. */
325 /* Approximate log base 2 of the number of time units per
326 biennium. A biennium is 2 years; use this unit instead of
327 years to avoid integer overflow. For example, 2 average
328 Gregorian years are 2 * 365.2425 * 24 * 60 * 60 seconds,
329 which is 63113904 seconds, and rint (log2 (63113904)) is
331 int ALOG2_SECONDS_PER_BIENNIUM = 26;
332 int ALOG2_MINUTES_PER_BIENNIUM = 20;
333 int ALOG2_HOURS_PER_BIENNIUM = 14;
334 int ALOG2_DAYS_PER_BIENNIUM = 10;
335 int LOG2_YEARS_PER_BIENNIUM = 1;
337 int approx_requested_biennia =
338 (SHR (year_requested, LOG2_YEARS_PER_BIENNIUM)
339 - SHR (EPOCH_YEAR - TM_YEAR_BASE, LOG2_YEARS_PER_BIENNIUM)
340 + SHR (mday, ALOG2_DAYS_PER_BIENNIUM)
341 + SHR (hour, ALOG2_HOURS_PER_BIENNIUM)
342 + SHR (min, ALOG2_MINUTES_PER_BIENNIUM)
343 + (LEAP_SECONDS_POSSIBLE
345 : SHR (sec, ALOG2_SECONDS_PER_BIENNIUM)));
347 int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM);
348 int diff = approx_biennia - approx_requested_biennia;
349 int abs_diff = diff < 0 ? - diff : diff;
351 /* IRIX 4.0.5 cc miscaculates TIME_T_MIN / 3: it erroneously
352 gives a positive value of 715827882. Setting a variable
353 first then doing math on it seems to work.
354 (ghazi@caip.rutgers.edu) */
355 time_t time_t_max = TIME_T_MAX;
356 time_t time_t_min = TIME_T_MIN;
357 time_t overflow_threshold =
358 (time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM;
360 if (overflow_threshold < abs_diff)
362 /* Overflow occurred. Try repairing it; this might work if
363 the time zone offset is enough to undo the overflow. */
364 time_t repaired_t0 = -1 - t0;
365 approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM);
366 diff = approx_biennia - approx_requested_biennia;
367 abs_diff = diff < 0 ? - diff : diff;
368 if (overflow_threshold < abs_diff)
370 guessed_offset += repaired_t0 - t0;
375 /* Repeatedly use the error to improve the guess. */
377 for (t = t1 = t2 = t0, dst2 = 0;
378 (gt = guess_time_tm (year, yday, hour, min, sec, &t,
379 ranged_convert (convert, &t, &tm)),
381 t1 = t2, t2 = t, t = gt, dst2 = tm.tm_isdst != 0)
382 if (t == t1 && t != t2
385 ? dst2 <= (tm.tm_isdst != 0)
386 : (isdst != 0) != (tm.tm_isdst != 0))))
387 /* We can't possibly find a match, as we are oscillating
388 between two values. The requested time probably falls
389 within a spring-forward gap of size GT - T. Follow the common
390 practice in this case, which is to return a time that is GT - T
391 away from the requested time, preferring a time whose
392 tm_isdst differs from the requested value. (If no tm_isdst
393 was requested and only one of the two values has a nonzero
394 tm_isdst, prefer that value.) In practice, this is more
395 useful than returning -1. */
397 else if (--remaining_probes == 0)
400 /* We have a match. Check whether tm.tm_isdst has the requested
402 if (isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
404 /* tm.tm_isdst has the wrong value. Look for a neighboring
405 time with the right value, and use its UTC offset.
407 Heuristic: probe the adjacent timestamps in both directions,
408 looking for the desired isdst. This should work for all real
409 time zone histories in the tz database. */
411 /* Distance between probes when looking for a DST boundary. In
412 tzdata2003a, the shortest period of DST is 601200 seconds
413 (e.g., America/Recife starting 2000-10-08 01:00), and the
414 shortest period of non-DST surrounded by DST is 694800
415 seconds (Africa/Tunis starting 1943-04-17 01:00). Use the
416 minimum of these two values, so we don't miss these short
417 periods when probing. */
420 /* The longest period of DST in tzdata2003a is 536454000 seconds
421 (e.g., America/Jujuy starting 1946-10-01 01:00). The longest
422 period of non-DST is much longer, but it makes no real sense
423 to search for more than a year of non-DST, so use the DST
425 int duration_max = 536454000;
427 /* Search in both directions, so the maximum distance is half
428 the duration; add the stride to avoid off-by-1 problems. */
429 int delta_bound = duration_max / 2 + stride;
431 int delta, direction;
433 for (delta = stride; delta < delta_bound; delta += stride)
434 for (direction = -1; direction <= 1; direction += 2)
436 time_t ot = t + delta * direction;
437 if ((ot < t) == (direction < 0))
440 ranged_convert (convert, &ot, &otm);
441 if (otm.tm_isdst == isdst)
443 /* We found the desired tm_isdst.
444 Extrapolate back to the desired time. */
445 t = guess_time_tm (year, yday, hour, min, sec, &ot, &otm);
446 ranged_convert (convert, &t, &tm);
454 *offset = guessed_offset + t - t0;
456 if (LEAP_SECONDS_POSSIBLE && sec_requested != tm.tm_sec)
458 /* Adjust time to reflect the tm_sec requested, not the normalized value.
459 Also, repair any damage from a false match due to a leap second. */
460 int sec_adjustment = (sec == 0 && tm.tm_sec == 60) - sec;
461 t1 = t + sec_requested;
462 t2 = t1 + sec_adjustment;
463 if (((t1 < t) != (sec_requested < 0))
464 | ((t2 < t1) != (sec_adjustment < 0))
465 | ! (*convert) (&t2, &tm))
475 /* FIXME: This should use a signed type wide enough to hold any UTC
476 offset in seconds. 'int' should be good enough for GNU code. We
477 can't fix this unilaterally though, as other modules invoke
478 __mktime_internal. */
479 static time_t localtime_offset;
481 /* Convert *TP to a time_t value. */
483 mktime (struct tm *tp)
486 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
487 time zone names contained in the external variable `tzname' shall
488 be set as if the tzset() function had been called. */
492 return __mktime_internal (tp, __localtime_r, &localtime_offset);
496 weak_alias (mktime, timelocal)
500 libc_hidden_def (mktime)
501 libc_hidden_weak (timelocal)
507 not_equal_tm (const struct tm *a, const struct tm *b)
509 return ((a->tm_sec ^ b->tm_sec)
510 | (a->tm_min ^ b->tm_min)
511 | (a->tm_hour ^ b->tm_hour)
512 | (a->tm_mday ^ b->tm_mday)
513 | (a->tm_mon ^ b->tm_mon)
514 | (a->tm_year ^ b->tm_year)
515 | (a->tm_yday ^ b->tm_yday)
516 | (a->tm_isdst ^ b->tm_isdst));
520 print_tm (const struct tm *tp)
523 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
524 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
525 tp->tm_hour, tp->tm_min, tp->tm_sec,
526 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
532 check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt)
534 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
538 printf (")\nyields (");
540 printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl);
548 main (int argc, char **argv)
551 struct tm tm, tmk, tml;
556 if ((argc == 3 || argc == 4)
557 && (sscanf (argv[1], "%d-%d-%d%c",
558 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
560 && (sscanf (argv[2], "%d:%d:%d%c",
561 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
564 tm.tm_year -= TM_YEAR_BASE;
566 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
569 lt = localtime (&tl);
575 printf ("mktime returns %ld == ", (long int) tl);
578 status = check_result (tl, tmk, tl, lt);
580 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
582 time_t from = atol (argv[1]);
583 time_t by = atol (argv[2]);
584 time_t to = atol (argv[3]);
587 for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
589 lt = localtime (&tl);
594 status |= check_result (tk, tmk, tl, &tml);
598 printf ("localtime (%ld) yields 0\n", (long int) tl);
602 if ((tl1 < tl) != (by < 0))
606 for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1)
608 /* Null benchmark. */
609 lt = localtime (&tl);
614 status |= check_result (tk, tmk, tl, &tml);
618 printf ("localtime (%ld) yields 0\n", (long int) tl);
622 if ((tl1 < tl) != (by < 0))
628 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
629 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
630 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
631 argv[0], argv[0], argv[0]);
640 compile-command: "gcc -DDEBUG -Wall -W -O -g mktime.c -o mktime"