1 /* Convert a `struct tm' to a time_t value.
2 Copyright (C) 1993-1999, 2002-2004, 2005 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Paul Eggert (eggert@twinsun.com).
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.
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.
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, write to the Free
18 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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. */
41 #include <string.h> /* For the real memcpy prototype. */
46 /* Make it work even if the system's libc has its own mktime routine. */
47 # define mktime my_mktime
50 /* Shift A right by B bits portably, by dividing A by 2**B and
51 truncating towards minus infinity. A and B should be free of side
52 effects, and B should be in the range 0 <= B <= INT_BITS - 2, where
53 INT_BITS is the number of useful bits in an int. GNU code can
54 assume that INT_BITS is at least 32.
56 ISO C99 says that A >> B is implementation-defined if A < 0. Some
57 implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift
58 right in the usual way when A < 0, so SHR falls back on division if
59 ordinary A >> B doesn't seem to be the usual signed shift. */
63 : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0))
65 /* The extra casts in the following macros work around compiler bugs,
66 e.g., in Cray C 5.0.3.0. */
68 /* True if the arithmetic type T is an integer type. bool counts as
70 #define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
72 /* True if negative values of the signed integer type T use two's
73 complement, ones' complement, or signed magnitude representation,
74 respectively. Much GNU code assumes two's complement, but some
75 people like to be portable to all possible C hosts. */
76 #define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
77 #define TYPE_ONES_COMPLEMENT(t) ((t) ~ (t) 0 == 0)
78 #define TYPE_SIGNED_MAGNITUDE(t) ((t) ~ (t) 0 < (t) -1)
80 /* True if the arithmetic type T is signed. */
81 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
83 /* The maximum and minimum values for the integer type T. These
84 macros have undefined behavior if T is signed and has padding bits.
85 If this is a problem for you, please let us know how to fix it for
87 #define TYPE_MINIMUM(t) \
88 ((t) (! TYPE_SIGNED (t) \
90 : TYPE_SIGNED_MAGNITUDE (t) \
92 : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
93 #define TYPE_MAXIMUM(t) \
94 ((t) (! TYPE_SIGNED (t) \
96 : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
99 # define TIME_T_MIN TYPE_MINIMUM (time_t)
102 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
104 #define TIME_T_MIDPOINT (SHR (TIME_T_MIN + TIME_T_MAX, 1) + 1)
106 /* Verify a requirement at compile-time (unlike assert, which is runtime). */
107 #define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
109 verify (time_t_is_integer
, TYPE_IS_INTEGER (time_t));
110 verify (twos_complement_arithmetic
, TYPE_TWOS_COMPLEMENT (int));
111 /* The code also assumes that signed integer overflow silently wraps
112 around, but this assumption can't be stated without causing a
113 diagnostic on some hosts. */
115 #define EPOCH_YEAR 1970
116 #define TM_YEAR_BASE 1900
117 verify (base_year_is_a_multiple_of_100
, TM_YEAR_BASE
% 100 == 0);
119 /* Return 1 if YEAR + TM_YEAR_BASE is a leap year. */
121 leapyear (long int year
)
123 /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
124 Also, work even if YEAR is negative. */
128 || ((year
/ 100) & 3) == (- (TM_YEAR_BASE
/ 100) & 3)));
131 /* How many days come before each month (0-12). */
135 const unsigned short int __mon_yday
[2][13] =
138 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
140 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
145 /* Portable standalone applications should supply a "time_r.h" that
146 declares a POSIX-compliant localtime_r, for the benefit of older
147 implementations that lack localtime_r or have a nonstandard one.
148 See the gnulib time_r module for one way to implement this. */
150 # undef __localtime_r
151 # define __localtime_r localtime_r
152 # define __mktime_internal mktime_internal
155 /* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
156 (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
157 were not adjusted between the time stamps.
159 The YEAR values uses the same numbering as TP->tm_year. Values
160 need not be in the usual range. However, YEAR1 must not be less
161 than 2 * INT_MIN or greater than 2 * INT_MAX.
163 The result may overflow. It is the caller's responsibility to
167 ydhms_diff (long int year1
, long int yday1
, int hour1
, int min1
, int sec1
,
168 int year0
, int yday0
, int hour0
, int min0
, int sec0
)
170 verify (C99_integer_division
, -1 / 2 == 0);
171 verify (long_int_year_and_yday_are_wide_enough
,
172 INT_MAX
<= LONG_MAX
/ 2 || TIME_T_MAX
<= UINT_MAX
);
174 /* Compute intervening leap days correctly even if year is negative.
175 Take care to avoid integer overflow here. */
176 int a4
= SHR (year1
, 2) + SHR (TM_YEAR_BASE
, 2) - ! (year1
& 3);
177 int b4
= SHR (year0
, 2) + SHR (TM_YEAR_BASE
, 2) - ! (year0
& 3);
178 int a100
= a4
/ 25 - (a4
% 25 < 0);
179 int b100
= b4
/ 25 - (b4
% 25 < 0);
180 int a400
= SHR (a100
, 2);
181 int b400
= SHR (b100
, 2);
182 int intervening_leap_days
= (a4
- b4
) - (a100
- b100
) + (a400
- b400
);
184 /* Compute the desired time in time_t precision. Overflow might
186 time_t tyear1
= year1
;
187 time_t years
= tyear1
- year0
;
188 time_t days
= 365 * years
+ yday1
- yday0
+ intervening_leap_days
;
189 time_t hours
= 24 * days
+ hour1
- hour0
;
190 time_t minutes
= 60 * hours
+ min1
- min0
;
191 time_t seconds
= 60 * minutes
+ sec1
- sec0
;
196 /* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC),
197 assuming that *T corresponds to *TP and that no clock adjustments
198 occurred between *TP and the desired time.
199 If TP is null, return a value not equal to *T; this avoids false matches.
200 If overflow occurs, yield the minimal or maximal value, except do not
201 yield a value equal to *T. */
203 guess_time_tm (long int year
, long int yday
, int hour
, int min
, int sec
,
204 const time_t *t
, const struct tm
*tp
)
208 time_t d
= ydhms_diff (year
, yday
, hour
, min
, sec
,
209 tp
->tm_year
, tp
->tm_yday
,
210 tp
->tm_hour
, tp
->tm_min
, tp
->tm_sec
);
212 if ((t1
< *t
) == (TYPE_SIGNED (time_t) ? d
< 0 : TIME_T_MAX
/ 2 < d
))
216 /* Overflow occurred one way or another. Return the nearest result
217 that is actually in range, except don't report a zero difference
218 if the actual difference is nonzero, as that would cause a false
220 return (*t
< TIME_T_MIDPOINT
221 ? TIME_T_MIN
+ (*t
== TIME_T_MIN
)
222 : TIME_T_MAX
- (*t
== TIME_T_MAX
));
225 /* Use CONVERT to convert *T to a broken down time in *TP.
226 If *T is out of range for conversion, adjust it so that
227 it is the nearest in-range value and then convert that. */
229 ranged_convert (struct tm
*(*convert
) (const time_t *, struct tm
*),
230 time_t *t
, struct tm
*tp
)
232 struct tm
*r
= convert (t
, tp
);
239 /* BAD is a known unconvertible time_t, and OK is a known good one.
240 Use binary search to narrow the range between BAD and OK until
242 while (bad
!= ok
+ (bad
< 0 ? -1 : 1))
244 time_t mid
= *t
= (bad
< 0
245 ? bad
+ ((ok
- bad
) >> 1)
246 : ok
+ ((bad
- ok
) >> 1));
256 /* The last conversion attempt failed;
257 revert to the most recent successful attempt. */
267 /* Convert *TP to a time_t value, inverting
268 the monotonic and mostly-unit-linear conversion function CONVERT.
269 Use *OFFSET to keep track of a guess at the offset of the result,
270 compared to what the result would be for UTC without leap seconds.
271 If *OFFSET's guess is correct, only one CONVERT call is needed.
272 This function is external because it is used also by timegm.c. */
274 __mktime_internal (struct tm
*tp
,
275 struct tm
*(*convert
) (const time_t *, struct tm
*),
278 time_t t
, gt
, t0
, t1
, t2
;
281 /* The maximum number of probes (calls to CONVERT) should be enough
282 to handle any combinations of time zone rule changes, solar time,
283 leap seconds, and oscillations around a spring-forward gap.
284 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
285 int remaining_probes
= 6;
287 /* Time requested. Copy it in case CONVERT modifies *TP; this can
288 occur if TP is localtime's returned value and CONVERT is localtime. */
289 int sec
= tp
->tm_sec
;
290 int min
= tp
->tm_min
;
291 int hour
= tp
->tm_hour
;
292 int mday
= tp
->tm_mday
;
293 int mon
= tp
->tm_mon
;
294 int year_requested
= tp
->tm_year
;
295 int isdst
= tp
->tm_isdst
;
297 /* 1 if the previous probe was DST. */
300 /* Ensure that mon is in range, and set year accordingly. */
301 int mon_remainder
= mon
% 12;
302 int negative_mon_remainder
= mon_remainder
< 0;
303 int mon_years
= mon
/ 12 - negative_mon_remainder
;
304 long int lyear_requested
= year_requested
;
305 long int year
= lyear_requested
+ mon_years
;
307 /* The other values need not be in range:
308 the remaining code handles minor overflows correctly,
309 assuming int and time_t arithmetic wraps around.
310 Major overflows are caught at the end. */
312 /* Calculate day of year from year, month, and day of month.
313 The result need not be in range. */
314 int mon_yday
= ((__mon_yday
[leapyear (year
)]
315 [mon_remainder
+ 12 * negative_mon_remainder
])
317 long int lmday
= mday
;
318 long int yday
= mon_yday
+ lmday
;
320 time_t guessed_offset
= *offset
;
322 int sec_requested
= sec
;
324 if (LEAP_SECONDS_POSSIBLE
)
326 /* Handle out-of-range seconds specially,
327 since ydhms_tm_diff assumes every minute has 60 seconds. */
334 /* Invert CONVERT by probing. First assume the same offset as last
337 t0
= ydhms_diff (year
, yday
, hour
, min
, sec
,
338 EPOCH_YEAR
- TM_YEAR_BASE
, 0, 0, 0, - guessed_offset
);
340 if (TIME_T_MAX
/ INT_MAX
/ 366 / 24 / 60 / 60 < 3)
342 /* time_t isn't large enough to rule out overflows, so check
343 for major overflows. A gross check suffices, since if t0
344 has overflowed, it is off by a multiple of TIME_T_MAX -
345 TIME_T_MIN + 1. So ignore any component of the difference
346 that is bounded by a small value. */
348 /* Approximate log base 2 of the number of time units per
349 biennium. A biennium is 2 years; use this unit instead of
350 years to avoid integer overflow. For example, 2 average
351 Gregorian years are 2 * 365.2425 * 24 * 60 * 60 seconds,
352 which is 63113904 seconds, and rint (log2 (63113904)) is
354 int ALOG2_SECONDS_PER_BIENNIUM
= 26;
355 int ALOG2_MINUTES_PER_BIENNIUM
= 20;
356 int ALOG2_HOURS_PER_BIENNIUM
= 14;
357 int ALOG2_DAYS_PER_BIENNIUM
= 10;
358 int LOG2_YEARS_PER_BIENNIUM
= 1;
360 int approx_requested_biennia
=
361 (SHR (year_requested
, LOG2_YEARS_PER_BIENNIUM
)
362 - SHR (EPOCH_YEAR
- TM_YEAR_BASE
, LOG2_YEARS_PER_BIENNIUM
)
363 + SHR (mday
, ALOG2_DAYS_PER_BIENNIUM
)
364 + SHR (hour
, ALOG2_HOURS_PER_BIENNIUM
)
365 + SHR (min
, ALOG2_MINUTES_PER_BIENNIUM
)
366 + (LEAP_SECONDS_POSSIBLE
368 : SHR (sec
, ALOG2_SECONDS_PER_BIENNIUM
)));
370 int approx_biennia
= SHR (t0
, ALOG2_SECONDS_PER_BIENNIUM
);
371 int diff
= approx_biennia
- approx_requested_biennia
;
372 int abs_diff
= diff
< 0 ? - diff
: diff
;
374 /* IRIX 4.0.5 cc miscaculates TIME_T_MIN / 3: it erroneously
375 gives a positive value of 715827882. Setting a variable
376 first then doing math on it seems to work.
377 (ghazi@caip.rutgers.edu) */
378 time_t time_t_max
= TIME_T_MAX
;
379 time_t time_t_min
= TIME_T_MIN
;
380 time_t overflow_threshold
=
381 (time_t_max
/ 3 - time_t_min
/ 3) >> ALOG2_SECONDS_PER_BIENNIUM
;
383 if (overflow_threshold
< abs_diff
)
385 /* Overflow occurred. Try repairing it; this might work if
386 the time zone offset is enough to undo the overflow. */
387 time_t repaired_t0
= -1 - t0
;
388 approx_biennia
= SHR (repaired_t0
, ALOG2_SECONDS_PER_BIENNIUM
);
389 diff
= approx_biennia
- approx_requested_biennia
;
390 abs_diff
= diff
< 0 ? - diff
: diff
;
391 if (overflow_threshold
< abs_diff
)
393 guessed_offset
+= repaired_t0
- t0
;
398 /* Repeatedly use the error to improve the guess. */
400 for (t
= t1
= t2
= t0
, dst2
= 0;
401 (gt
= guess_time_tm (year
, yday
, hour
, min
, sec
, &t
,
402 ranged_convert (convert
, &t
, &tm
)),
404 t1
= t2
, t2
= t
, t
= gt
, dst2
= tm
.tm_isdst
!= 0)
405 if (t
== t1
&& t
!= t2
408 ? dst2
<= (tm
.tm_isdst
!= 0)
409 : (isdst
!= 0) != (tm
.tm_isdst
!= 0))))
410 /* We can't possibly find a match, as we are oscillating
411 between two values. The requested time probably falls
412 within a spring-forward gap of size GT - T. Follow the common
413 practice in this case, which is to return a time that is GT - T
414 away from the requested time, preferring a time whose
415 tm_isdst differs from the requested value. (If no tm_isdst
416 was requested and only one of the two values has a nonzero
417 tm_isdst, prefer that value.) In practice, this is more
418 useful than returning -1. */
420 else if (--remaining_probes
== 0)
423 /* We have a match. Check whether tm.tm_isdst has the requested
425 if (isdst
!= tm
.tm_isdst
&& 0 <= isdst
&& 0 <= tm
.tm_isdst
)
427 /* tm.tm_isdst has the wrong value. Look for a neighboring
428 time with the right value, and use its UTC offset.
430 Heuristic: probe the adjacent timestamps in both directions,
431 looking for the desired isdst. This should work for all real
432 time zone histories in the tz database. */
434 /* Distance between probes when looking for a DST boundary. In
435 tzdata2003a, the shortest period of DST is 601200 seconds
436 (e.g., America/Recife starting 2000-10-08 01:00), and the
437 shortest period of non-DST surrounded by DST is 694800
438 seconds (Africa/Tunis starting 1943-04-17 01:00). Use the
439 minimum of these two values, so we don't miss these short
440 periods when probing. */
443 /* The longest period of DST in tzdata2003a is 536454000 seconds
444 (e.g., America/Jujuy starting 1946-10-01 01:00). The longest
445 period of non-DST is much longer, but it makes no real sense
446 to search for more than a year of non-DST, so use the DST
448 int duration_max
= 536454000;
450 /* Search in both directions, so the maximum distance is half
451 the duration; add the stride to avoid off-by-1 problems. */
452 int delta_bound
= duration_max
/ 2 + stride
;
454 int delta
, direction
;
456 for (delta
= stride
; delta
< delta_bound
; delta
+= stride
)
457 for (direction
= -1; direction
<= 1; direction
+= 2)
459 time_t ot
= t
+ delta
* direction
;
460 if ((ot
< t
) == (direction
< 0))
463 ranged_convert (convert
, &ot
, &otm
);
464 if (otm
.tm_isdst
== isdst
)
466 /* We found the desired tm_isdst.
467 Extrapolate back to the desired time. */
468 t
= guess_time_tm (year
, yday
, hour
, min
, sec
, &ot
, &otm
);
469 ranged_convert (convert
, &t
, &tm
);
477 *offset
= guessed_offset
+ t
- t0
;
479 if (LEAP_SECONDS_POSSIBLE
&& sec_requested
!= tm
.tm_sec
)
481 /* Adjust time to reflect the tm_sec requested, not the normalized value.
482 Also, repair any damage from a false match due to a leap second. */
483 int sec_adjustment
= (sec
== 0 && tm
.tm_sec
== 60) - sec
;
484 t1
= t
+ sec_requested
;
485 t2
= t1
+ sec_adjustment
;
486 if (((t1
< t
) != (sec_requested
< 0))
487 | ((t2
< t1
) != (sec_adjustment
< 0))
488 | ! convert (&t2
, &tm
))
498 /* FIXME: This should use a signed type wide enough to hold any UTC
499 offset in seconds. 'int' should be good enough for GNU code. We
500 can't fix this unilaterally though, as other modules invoke
501 __mktime_internal. */
502 static time_t localtime_offset
;
504 /* Convert *TP to a time_t value. */
506 mktime (struct tm
*tp
)
509 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
510 time zone names contained in the external variable `tzname' shall
511 be set as if the tzset() function had been called. */
515 return __mktime_internal (tp
, __localtime_r
, &localtime_offset
);
519 weak_alias (mktime
, timelocal
)
523 libc_hidden_def (mktime
)
524 libc_hidden_weak (timelocal
)
530 not_equal_tm (const struct tm
*a
, const struct tm
*b
)
532 return ((a
->tm_sec
^ b
->tm_sec
)
533 | (a
->tm_min
^ b
->tm_min
)
534 | (a
->tm_hour
^ b
->tm_hour
)
535 | (a
->tm_mday
^ b
->tm_mday
)
536 | (a
->tm_mon
^ b
->tm_mon
)
537 | (a
->tm_year
^ b
->tm_year
)
538 | (a
->tm_yday
^ b
->tm_yday
)
539 | (a
->tm_isdst
^ b
->tm_isdst
));
543 print_tm (const struct tm
*tp
)
546 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
547 tp
->tm_year
+ TM_YEAR_BASE
, tp
->tm_mon
+ 1, tp
->tm_mday
,
548 tp
->tm_hour
, tp
->tm_min
, tp
->tm_sec
,
549 tp
->tm_yday
, tp
->tm_wday
, tp
->tm_isdst
);
555 check_result (time_t tk
, struct tm tmk
, time_t tl
, const struct tm
*lt
)
557 if (tk
!= tl
|| !lt
|| not_equal_tm (&tmk
, lt
))
561 printf (")\nyields (");
563 printf (") == %ld, should be %ld\n", (long int) tk
, (long int) tl
);
571 main (int argc
, char **argv
)
574 struct tm tm
, tmk
, tml
;
579 if ((argc
== 3 || argc
== 4)
580 && (sscanf (argv
[1], "%d-%d-%d%c",
581 &tm
.tm_year
, &tm
.tm_mon
, &tm
.tm_mday
, &trailer
)
583 && (sscanf (argv
[2], "%d:%d:%d%c",
584 &tm
.tm_hour
, &tm
.tm_min
, &tm
.tm_sec
, &trailer
)
587 tm
.tm_year
-= TM_YEAR_BASE
;
589 tm
.tm_isdst
= argc
== 3 ? -1 : atoi (argv
[3]);
592 lt
= localtime (&tl
);
598 printf ("mktime returns %ld == ", (long int) tl
);
601 status
= check_result (tl
, tmk
, tl
, lt
);
603 else if (argc
== 4 || (argc
== 5 && strcmp (argv
[4], "-") == 0))
605 time_t from
= atol (argv
[1]);
606 time_t by
= atol (argv
[2]);
607 time_t to
= atol (argv
[3]);
610 for (tl
= from
; by
< 0 ? to
<= tl
: tl
<= to
; tl
= tl1
)
612 lt
= localtime (&tl
);
617 status
|= check_result (tk
, tmk
, tl
, &tml
);
621 printf ("localtime (%ld) yields 0\n", (long int) tl
);
625 if ((tl1
< tl
) != (by
< 0))
629 for (tl
= from
; by
< 0 ? to
<= tl
: tl
<= to
; tl
= tl1
)
631 /* Null benchmark. */
632 lt
= localtime (&tl
);
637 status
|= check_result (tk
, tmk
, tl
, &tml
);
641 printf ("localtime (%ld) yields 0\n", (long int) tl
);
645 if ((tl1
< tl
) != (by
< 0))
651 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
652 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
653 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
654 argv
[0], argv
[0], argv
[0]);
663 compile-command: "gcc -DDEBUG -Wall -W -O -g mktime.c -o mktime"