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 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. */
45 /* Make it work even if the system's libc has its own mktime routine. */
46 # define mktime my_mktime
49 /* The extra casts work around common compiler bugs. */
50 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
51 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
52 It is necessary at least when t == time_t. */
53 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
54 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
55 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
58 # define TIME_T_MIN TYPE_MINIMUM (time_t)
61 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
64 /* Verify a requirement at compile-time (unlike assert, which is runtime). */
65 #define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
67 verify (time_t_is_integer
, (time_t) 0.5 == 0);
68 verify (twos_complement_arithmetic
, -1 == ~1 + 1);
69 verify (right_shift_propagates_sign
, -1 >> 1 == -1);
70 /* The code also assumes that signed integer overflow silently wraps
71 around, but this assumption can't be stated without causing a
72 diagnostic on some hosts. */
74 #define EPOCH_YEAR 1970
75 #define TM_YEAR_BASE 1900
76 verify (base_year_is_a_multiple_of_100
, TM_YEAR_BASE
% 100 == 0);
78 /* Return 1 if YEAR + TM_YEAR_BASE is a leap year. */
82 /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
83 Also, work even if YEAR is negative. */
87 || ((year
/ 100) & 3) == (- (TM_YEAR_BASE
/ 100) & 3)));
90 /* How many days come before each month (0-12). */
94 const unsigned short int __mon_yday
[2][13] =
97 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
99 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
104 /* Portable standalone applications should supply a "time_r.h" that
105 declares a POSIX-compliant localtime_r, for the benefit of older
106 implementations that lack localtime_r or have a nonstandard one.
107 See the gnulib time_r module for one way to implement this. */
109 # undef __localtime_r
110 # define __localtime_r localtime_r
111 # define __mktime_internal mktime_internal
115 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
116 measured in seconds, ignoring leap seconds.
117 YEAR uses the same numbering as TM->tm_year.
118 All values are in range, except possibly YEAR.
119 If TP is null, return a nonzero value.
120 If overflow occurs, yield the low order bits of the correct answer. */
122 ydhms_tm_diff (int year
, int yday
, int hour
, int min
, int sec
,
129 verify (C99_integer_division
, -1 / 2 == 0);
131 /* Compute intervening leap days correctly even if year is negative.
132 Take care to avoid int overflow. time_t overflow is OK, since
133 only the low order bits of the correct time_t answer are needed.
134 Don't convert to time_t until after all divisions are done, since
135 time_t might be unsigned. */
136 int a4
= (year
>> 2) + (TM_YEAR_BASE
>> 2) - ! (year
& 3);
137 int b4
= (tp
->tm_year
>> 2) + (TM_YEAR_BASE
>> 2) - ! (tp
->tm_year
& 3);
138 int a100
= a4
/ 25 - (a4
% 25 < 0);
139 int b100
= b4
/ 25 - (b4
% 25 < 0);
140 int a400
= a100
>> 2;
141 int b400
= b100
>> 2;
142 int intervening_leap_days
= (a4
- b4
) - (a100
- b100
) + (a400
- b400
);
143 time_t years
= year
- (time_t) tp
->tm_year
;
144 time_t days
= (365 * years
+ intervening_leap_days
145 + (yday
- tp
->tm_yday
));
146 return (60 * (60 * (24 * days
+ (hour
- tp
->tm_hour
))
147 + (min
- tp
->tm_min
))
148 + (sec
- tp
->tm_sec
));
152 /* Use CONVERT to convert *T to a broken down time in *TP.
153 If *T is out of range for conversion, adjust it so that
154 it is the nearest in-range value and then convert that. */
156 ranged_convert (struct tm
*(*convert
) (const time_t *, struct tm
*),
157 time_t *t
, struct tm
*tp
)
161 if (! (r
= (*convert
) (t
, tp
)) && *t
)
167 /* BAD is a known unconvertible time_t, and OK is a known good one.
168 Use binary search to narrow the range between BAD and OK until
170 while (bad
!= ok
+ (bad
< 0 ? -1 : 1))
172 time_t mid
= *t
= (bad
< 0
173 ? bad
+ ((ok
- bad
) >> 1)
174 : ok
+ ((bad
- ok
) >> 1));
175 if ((r
= (*convert
) (t
, tp
)))
186 /* The last conversion attempt failed;
187 revert to the most recent successful attempt. */
198 /* Convert *TP to a time_t value, inverting
199 the monotonic and mostly-unit-linear conversion function CONVERT.
200 Use *OFFSET to keep track of a guess at the offset of the result,
201 compared to what the result would be for UTC without leap seconds.
202 If *OFFSET's guess is correct, only one CONVERT call is needed. */
204 __mktime_internal (struct tm
*tp
,
205 struct tm
*(*convert
) (const time_t *, struct tm
*),
208 time_t t
, dt
, t0
, t1
, t2
;
211 /* The maximum number of probes (calls to CONVERT) should be enough
212 to handle any combinations of time zone rule changes, solar time,
213 leap seconds, and oscillations around a spring-forward gap.
214 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
215 int remaining_probes
= 6;
217 /* Time requested. Copy it in case CONVERT modifies *TP; this can
218 occur if TP is localtime's returned value and CONVERT is localtime. */
219 int sec
= tp
->tm_sec
;
220 int min
= tp
->tm_min
;
221 int hour
= tp
->tm_hour
;
222 int mday
= tp
->tm_mday
;
223 int mon
= tp
->tm_mon
;
224 int year_requested
= tp
->tm_year
;
225 int isdst
= tp
->tm_isdst
;
227 /* 1 if the previous probe was DST. */
230 /* Ensure that mon is in range, and set year accordingly. */
231 int mon_remainder
= mon
% 12;
232 int negative_mon_remainder
= mon_remainder
< 0;
233 int mon_years
= mon
/ 12 - negative_mon_remainder
;
234 int year
= year_requested
+ mon_years
;
236 /* The other values need not be in range:
237 the remaining code handles minor overflows correctly,
238 assuming int and time_t arithmetic wraps around.
239 Major overflows are caught at the end. */
241 /* Calculate day of year from year, month, and day of month.
242 The result need not be in range. */
243 int yday
= ((__mon_yday
[leapyear (year
)]
244 [mon_remainder
+ 12 * negative_mon_remainder
])
247 int sec_requested
= sec
;
249 /* Only years after 1970 are defined.
250 If year is 69, it might still be representable due to
251 timezone differences. */
255 #if LEAP_SECONDS_POSSIBLE
256 /* Handle out-of-range seconds specially,
257 since ydhms_tm_diff assumes every minute has 60 seconds. */
264 /* Invert CONVERT by probing. First assume the same offset as last time.
265 Then repeatedly use the error to improve the guess. */
267 tm
.tm_year
= EPOCH_YEAR
- TM_YEAR_BASE
;
268 tm
.tm_yday
= tm
.tm_hour
= tm
.tm_min
= tm
.tm_sec
= 0;
269 t0
= ydhms_tm_diff (year
, yday
, hour
, min
, sec
, &tm
);
271 for (t
= t1
= t2
= t0
+ *offset
, dst2
= 0;
272 (dt
= ydhms_tm_diff (year
, yday
, hour
, min
, sec
,
273 ranged_convert (convert
, &t
, &tm
)));
274 t1
= t2
, t2
= t
, t
+= dt
, dst2
= tm
.tm_isdst
!= 0)
275 if (t
== t1
&& t
!= t2
278 ? dst2
<= (tm
.tm_isdst
!= 0)
279 : (isdst
!= 0) != (tm
.tm_isdst
!= 0))))
280 /* We can't possibly find a match, as we are oscillating
281 between two values. The requested time probably falls
282 within a spring-forward gap of size DT. Follow the common
283 practice in this case, which is to return a time that is DT
284 away from the requested time, preferring a time whose
285 tm_isdst differs from the requested value. (If no tm_isdst
286 was requested and only one of the two values has a nonzero
287 tm_isdst, prefer that value.) In practice, this is more
288 useful than returning -1. */
290 else if (--remaining_probes
== 0)
293 /* If we have a match, check whether tm.tm_isdst has the requested
295 if (dt
== 0 && isdst
!= tm
.tm_isdst
&& 0 <= isdst
&& 0 <= tm
.tm_isdst
)
297 /* tm.tm_isdst has the wrong value. Look for a neighboring
298 time with the right value, and use its UTC offset.
299 Heuristic: probe the previous three calendar quarters (approximately),
300 looking for the desired isdst. This isn't perfect,
301 but it's good enough in practice. */
302 int quarter
= 7889238; /* seconds per average 1/4 Gregorian year */
305 /* If we're too close to the time_t limit, look in future quarters. */
306 if (t
< TIME_T_MIN
+ 3 * quarter
)
309 for (i
= 1; i
<= 3; i
++)
311 time_t ot
= t
- i
* quarter
;
313 ranged_convert (convert
, &ot
, &otm
);
314 if (otm
.tm_isdst
== isdst
)
316 /* We found the desired tm_isdst.
317 Extrapolate back to the desired time. */
318 t
= ot
+ ydhms_tm_diff (year
, yday
, hour
, min
, sec
, &otm
);
319 ranged_convert (convert
, &t
, &tm
);
327 #if LEAP_SECONDS_POSSIBLE
328 if (sec_requested
!= tm
.tm_sec
)
330 /* Adjust time to reflect the tm_sec requested, not the normalized value.
331 Also, repair any damage from a false match due to a leap second. */
332 t
+= sec_requested
- sec
+ (sec
== 0 && tm
.tm_sec
== 60);
333 if (! (*convert
) (&t
, &tm
))
338 if (TIME_T_MAX
/ INT_MAX
/ 366 / 24 / 60 / 60 < 3)
340 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
341 so check for major overflows. A gross check suffices,
342 since if t has overflowed, it is off by a multiple of
343 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
344 the difference that is bounded by a small value. */
346 double dyear
= (double) year_requested
+ mon_years
- tm
.tm_year
;
347 double dday
= 366 * dyear
+ mday
;
348 double dsec
= 60 * (60 * (24 * dday
+ hour
) + min
) + sec_requested
;
350 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
351 correct results, ie., it erroneously gives a positive value
352 of 715827882. Setting a variable first then doing math on it
353 seems to work. (ghazi@caip.rutgers.edu) */
355 const time_t time_t_max
= TIME_T_MAX
;
356 const time_t time_t_min
= TIME_T_MIN
;
358 if (time_t_max
/ 3 - time_t_min
/ 3 < (dsec
< 0 ? - dsec
: dsec
))
364 /* If year was 69, need to check whether the time was representable
366 if (t
< 0 || t
> 2 * 24 * 60 * 60)
375 static time_t localtime_offset
;
377 /* Convert *TP to a time_t value. */
379 mktime (struct tm
*tp
)
382 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
383 time zone names contained in the external variable `tzname' shall
384 be set as if the tzset() function had been called. */
388 return __mktime_internal (tp
, __localtime_r
, &localtime_offset
);
392 weak_alias (mktime
, timelocal
)
396 libc_hidden_def (mktime
)
397 libc_hidden_weak (timelocal
)
403 not_equal_tm (const struct tm
*a
, const struct tm
*b
)
405 return ((a
->tm_sec
^ b
->tm_sec
)
406 | (a
->tm_min
^ b
->tm_min
)
407 | (a
->tm_hour
^ b
->tm_hour
)
408 | (a
->tm_mday
^ b
->tm_mday
)
409 | (a
->tm_mon
^ b
->tm_mon
)
410 | (a
->tm_year
^ b
->tm_year
)
411 | (a
->tm_mday
^ b
->tm_mday
)
412 | (a
->tm_yday
^ b
->tm_yday
)
413 | (a
->tm_isdst
^ b
->tm_isdst
));
417 print_tm (const struct tm
*tp
)
420 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
421 tp
->tm_year
+ TM_YEAR_BASE
, tp
->tm_mon
+ 1, tp
->tm_mday
,
422 tp
->tm_hour
, tp
->tm_min
, tp
->tm_sec
,
423 tp
->tm_yday
, tp
->tm_wday
, tp
->tm_isdst
);
429 check_result (time_t tk
, struct tm tmk
, time_t tl
, const struct tm
*lt
)
431 if (tk
!= tl
|| !lt
|| not_equal_tm (&tmk
, lt
))
435 printf (")\nyields (");
437 printf (") == %ld, should be %ld\n", (long int) tk
, (long int) tl
);
445 main (int argc
, char **argv
)
448 struct tm tm
, tmk
, tml
;
453 if ((argc
== 3 || argc
== 4)
454 && (sscanf (argv
[1], "%d-%d-%d%c",
455 &tm
.tm_year
, &tm
.tm_mon
, &tm
.tm_mday
, &trailer
)
457 && (sscanf (argv
[2], "%d:%d:%d%c",
458 &tm
.tm_hour
, &tm
.tm_min
, &tm
.tm_sec
, &trailer
)
461 tm
.tm_year
-= TM_YEAR_BASE
;
463 tm
.tm_isdst
= argc
== 3 ? -1 : atoi (argv
[3]);
466 lt
= localtime (&tl
);
472 printf ("mktime returns %ld == ", (long int) tl
);
475 status
= check_result (tl
, tmk
, tl
, lt
);
477 else if (argc
== 4 || (argc
== 5 && strcmp (argv
[4], "-") == 0))
479 time_t from
= atol (argv
[1]);
480 time_t by
= atol (argv
[2]);
481 time_t to
= atol (argv
[3]);
484 for (tl
= from
; by
< 0 ? to
<= tl
: tl
<= to
; tl
= tl1
)
486 lt
= localtime (&tl
);
491 status
|= check_result (tk
, tmk
, tl
, &tml
);
495 printf ("localtime (%ld) yields 0\n", (long int) tl
);
499 if ((tl1
< tl
) != (by
< 0))
503 for (tl
= from
; by
< 0 ? to
<= tl
: tl
<= to
; tl
= tl1
)
505 /* Null benchmark. */
506 lt
= localtime (&tl
);
511 status
|= check_result (tk
, tmk
, tl
, &tml
);
515 printf ("localtime (%ld) yields 0\n", (long int) tl
);
519 if ((tl1
< tl
) != (by
< 0))
525 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
526 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
527 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
528 argv
[0], argv
[0], argv
[0]);
537 compile-command: "gcc -DDEBUG -Wall -W -O -g mktime.c -o mktime"