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[glibc.git] / time / mktime.c
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1 /* Convert a `struct tm' to a time_t value.
2 Copyright (C) 1993-1999, 2002 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
19 02111-1307 USA. */
21 /* Define this to have a standalone program to test this implementation of
22 mktime. */
23 /* #define DEBUG 1 */
25 #ifdef HAVE_CONFIG_H
26 # include <config.h>
27 #endif
29 #ifdef _LIBC
30 # define HAVE_LIMITS_H 1
31 # define STDC_HEADERS 1
32 #endif
34 /* Assume that leap seconds are possible, unless told otherwise.
35 If the host has a `zic' command with a `-L leapsecondfilename' option,
36 then it supports leap seconds; otherwise it probably doesn't. */
37 #ifndef LEAP_SECONDS_POSSIBLE
38 # define LEAP_SECONDS_POSSIBLE 1
39 #endif
41 #include <sys/types.h> /* Some systems define `time_t' here. */
42 #include <time.h>
44 #if HAVE_LIMITS_H
45 # include <limits.h>
46 #endif
48 #if DEBUG
49 # include <stdio.h>
50 # if STDC_HEADERS
51 # include <stdlib.h>
52 # include <string.h>
53 # endif
54 /* Make it work even if the system's libc has its own mktime routine. */
55 # define mktime my_mktime
56 #endif /* DEBUG */
58 #ifndef __P
59 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
60 # define __P(args) args
61 # else
62 # define __P(args) ()
63 # endif /* GCC. */
64 #endif /* Not __P. */
66 #ifndef CHAR_BIT
67 # define CHAR_BIT 8
68 #endif
70 /* The extra casts work around common compiler bugs. */
71 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
72 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
73 It is necessary at least when t == time_t. */
74 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
75 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
76 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
78 #ifndef INT_MIN
79 # define INT_MIN TYPE_MINIMUM (int)
80 #endif
81 #ifndef INT_MAX
82 # define INT_MAX TYPE_MAXIMUM (int)
83 #endif
85 #ifndef TIME_T_MIN
86 # define TIME_T_MIN TYPE_MINIMUM (time_t)
87 #endif
88 #ifndef TIME_T_MAX
89 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
90 #endif
92 #define TM_YEAR_BASE 1900
93 #define EPOCH_YEAR 1970
95 #ifndef __isleap
96 /* Nonzero if YEAR is a leap year (every 4 years,
97 except every 100th isn't, and every 400th is). */
98 # define __isleap(year) \
99 ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
100 #endif
102 /* How many days come before each month (0-12). */
103 const unsigned short int __mon_yday[2][13] =
105 /* Normal years. */
106 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
107 /* Leap years. */
108 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
112 #ifdef _LIBC
113 # define my_mktime_localtime_r __localtime_r
114 #else
115 /* If we're a mktime substitute in a GNU program, then prefer
116 localtime to localtime_r, since many localtime_r implementations
117 are buggy. */
118 static struct tm *
119 my_mktime_localtime_r (const time_t *t, struct tm *tp)
121 struct tm *l = localtime (t);
122 if (! l)
123 return 0;
124 *tp = *l;
125 return tp;
127 #endif /* ! _LIBC */
130 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
131 measured in seconds, ignoring leap seconds.
132 YEAR uses the same numbering as TM->tm_year.
133 All values are in range, except possibly YEAR.
134 If TP is null, return a nonzero value.
135 If overflow occurs, yield the low order bits of the correct answer. */
136 static time_t
137 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
138 const struct tm *tp)
140 if (!tp)
141 return 1;
142 else
144 /* Compute intervening leap days correctly even if year is negative.
145 Take care to avoid int overflow. time_t overflow is OK, since
146 only the low order bits of the correct time_t answer are needed.
147 Don't convert to time_t until after all divisions are done, since
148 time_t might be unsigned. */
149 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
150 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
151 int a100 = a4 / 25 - (a4 % 25 < 0);
152 int b100 = b4 / 25 - (b4 % 25 < 0);
153 int a400 = a100 >> 2;
154 int b400 = b100 >> 2;
155 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
156 time_t years = year - (time_t) tp->tm_year;
157 time_t days = (365 * years + intervening_leap_days
158 + (yday - tp->tm_yday));
159 return (60 * (60 * (24 * days + (hour - tp->tm_hour))
160 + (min - tp->tm_min))
161 + (sec - tp->tm_sec));
165 /* Use CONVERT to convert *T to a broken down time in *TP.
166 If *T is out of range for conversion, adjust it so that
167 it is the nearest in-range value and then convert that. */
168 static struct tm *
169 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
170 time_t *t, struct tm *tp)
172 struct tm *r;
174 if (! (r = (*convert) (t, tp)) && *t)
176 time_t bad = *t;
177 time_t ok = 0;
178 struct tm tm;
180 /* BAD is a known unconvertible time_t, and OK is a known good one.
181 Use binary search to narrow the range between BAD and OK until
182 they differ by 1. */
183 while (bad != ok + (bad < 0 ? -1 : 1))
185 time_t mid = *t = (bad < 0
186 ? bad + ((ok - bad) >> 1)
187 : ok + ((bad - ok) >> 1));
188 if ((r = (*convert) (t, tp)))
190 tm = *r;
191 ok = mid;
193 else
194 bad = mid;
197 if (!r && ok)
199 /* The last conversion attempt failed;
200 revert to the most recent successful attempt. */
201 *t = ok;
202 *tp = tm;
203 r = tp;
207 return r;
211 /* Convert *TP to a time_t value, inverting
212 the monotonic and mostly-unit-linear conversion function CONVERT.
213 Use *OFFSET to keep track of a guess at the offset of the result,
214 compared to what the result would be for UTC without leap seconds.
215 If *OFFSET's guess is correct, only one CONVERT call is needed. */
216 time_t
217 __mktime_internal (struct tm *tp,
218 struct tm *(*convert) (const time_t *, struct tm *),
219 time_t *offset)
221 time_t t, dt, t0, t1, t2;
222 struct tm tm;
224 /* The maximum number of probes (calls to CONVERT) should be enough
225 to handle any combinations of time zone rule changes, solar time,
226 leap seconds, and oscillations around a spring-forward gap.
227 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
228 int remaining_probes = 6;
230 /* Time requested. Copy it in case CONVERT modifies *TP; this can
231 occur if TP is localtime's returned value and CONVERT is localtime. */
232 int sec = tp->tm_sec;
233 int min = tp->tm_min;
234 int hour = tp->tm_hour;
235 int mday = tp->tm_mday;
236 int mon = tp->tm_mon;
237 int year_requested = tp->tm_year;
238 int isdst = tp->tm_isdst;
240 /* 1 if the previous probe was DST. */
241 int dst2;
243 /* Ensure that mon is in range, and set year accordingly. */
244 int mon_remainder = mon % 12;
245 int negative_mon_remainder = mon_remainder < 0;
246 int mon_years = mon / 12 - negative_mon_remainder;
247 int year = year_requested + mon_years;
249 /* The other values need not be in range:
250 the remaining code handles minor overflows correctly,
251 assuming int and time_t arithmetic wraps around.
252 Major overflows are caught at the end. */
254 /* Calculate day of year from year, month, and day of month.
255 The result need not be in range. */
256 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
257 [mon_remainder + 12 * negative_mon_remainder])
258 + mday - 1);
260 int sec_requested = sec;
262 /* Only years after 1970 are defined.
263 If year is 69, it might still be representable due to
264 timezone differences. */
265 if (year < 69)
266 return -1;
268 #if LEAP_SECONDS_POSSIBLE
269 /* Handle out-of-range seconds specially,
270 since ydhms_tm_diff assumes every minute has 60 seconds. */
271 if (sec < 0)
272 sec = 0;
273 if (59 < sec)
274 sec = 59;
275 #endif
277 /* Invert CONVERT by probing. First assume the same offset as last time.
278 Then repeatedly use the error to improve the guess. */
280 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
281 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
282 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
284 for (t = t1 = t2 = t0 + *offset, dst2 = 0;
285 (dt = ydhms_tm_diff (year, yday, hour, min, sec,
286 ranged_convert (convert, &t, &tm)));
287 t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
288 if (t == t1 && t != t2
289 && (tm.tm_isdst < 0
290 || (isdst < 0
291 ? dst2 <= (tm.tm_isdst != 0)
292 : (isdst != 0) != (tm.tm_isdst != 0))))
293 /* We can't possibly find a match, as we are oscillating
294 between two values. The requested time probably falls
295 within a spring-forward gap of size DT. Follow the common
296 practice in this case, which is to return a time that is DT
297 away from the requested time, preferring a time whose
298 tm_isdst differs from the requested value. (If no tm_isdst
299 was requested and only one of the two values has a nonzero
300 tm_isdst, prefer that value.) In practice, this is more
301 useful than returning -1. */
302 break;
303 else if (--remaining_probes == 0)
304 return -1;
306 /* If we have a match, check whether tm.tm_isdst has the requested
307 value, if any. */
308 if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
310 /* tm.tm_isdst has the wrong value. Look for a neighboring
311 time with the right value, and use its UTC offset.
312 Heuristic: probe the previous three calendar quarters (approximately),
313 looking for the desired isdst. This isn't perfect,
314 but it's good enough in practice. */
315 int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
316 int i;
318 /* If we're too close to the time_t limit, look in future quarters. */
319 if (t < TIME_T_MIN + 3 * quarter)
320 quarter = -quarter;
322 for (i = 1; i <= 3; i++)
324 time_t ot = t - i * quarter;
325 struct tm otm;
326 ranged_convert (convert, &ot, &otm);
327 if (otm.tm_isdst == isdst)
329 /* We found the desired tm_isdst.
330 Extrapolate back to the desired time. */
331 t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
332 ranged_convert (convert, &t, &tm);
333 break;
338 *offset = t - t0;
340 #if LEAP_SECONDS_POSSIBLE
341 if (sec_requested != tm.tm_sec)
343 /* Adjust time to reflect the tm_sec requested, not the normalized value.
344 Also, repair any damage from a false match due to a leap second. */
345 t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
346 if (! (*convert) (&t, &tm))
347 return -1;
349 #endif
351 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
353 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
354 so check for major overflows. A gross check suffices,
355 since if t has overflowed, it is off by a multiple of
356 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
357 the difference that is bounded by a small value. */
359 double dyear = (double) year_requested + mon_years - tm.tm_year;
360 double dday = 366 * dyear + mday;
361 double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
363 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
364 correct results, ie., it erroneously gives a positive value
365 of 715827882. Setting a variable first then doing math on it
366 seems to work. (ghazi@caip.rutgers.edu) */
368 const time_t time_t_max = TIME_T_MAX;
369 const time_t time_t_min = TIME_T_MIN;
371 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
372 return -1;
375 if (year == 69)
377 /* If year was 69, need to check whether the time was representable
378 or not. */
379 if (t < 0 || t > 2 * 24 * 60 * 60)
380 return -1;
383 *tp = tm;
384 return t;
388 static time_t localtime_offset;
390 /* Convert *TP to a time_t value. */
391 time_t
392 mktime (tp)
393 struct tm *tp;
395 #ifdef _LIBC
396 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
397 time zone names contained in the external variable `tzname' shall
398 be set as if the tzset() function had been called. */
399 __tzset ();
400 #endif
402 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
405 #ifdef weak_alias
406 weak_alias (mktime, timelocal)
407 #endif
409 #ifdef _LIBC
410 libc_hidden_def (mktime)
411 libc_hidden_weak (timelocal)
412 #endif
414 #if DEBUG
416 static int
417 not_equal_tm (a, b)
418 struct tm *a;
419 struct tm *b;
421 return ((a->tm_sec ^ b->tm_sec)
422 | (a->tm_min ^ b->tm_min)
423 | (a->tm_hour ^ b->tm_hour)
424 | (a->tm_mday ^ b->tm_mday)
425 | (a->tm_mon ^ b->tm_mon)
426 | (a->tm_year ^ b->tm_year)
427 | (a->tm_mday ^ b->tm_mday)
428 | (a->tm_yday ^ b->tm_yday)
429 | (a->tm_isdst ^ b->tm_isdst));
432 static void
433 print_tm (tp)
434 struct tm *tp;
436 if (tp)
437 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
438 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
439 tp->tm_hour, tp->tm_min, tp->tm_sec,
440 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
441 else
442 printf ("0");
445 static int
446 check_result (tk, tmk, tl, lt)
447 time_t tk;
448 struct tm tmk;
449 time_t tl;
450 struct tm *lt;
452 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
454 printf ("mktime (");
455 print_tm (&tmk);
456 printf (")\nyields (");
457 print_tm (lt);
458 printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
459 return 1;
462 return 0;
466 main (argc, argv)
467 int argc;
468 char **argv;
470 int status = 0;
471 struct tm tm, tmk, tml;
472 struct tm *lt;
473 time_t tk, tl;
474 char trailer;
476 if ((argc == 3 || argc == 4)
477 && (sscanf (argv[1], "%d-%d-%d%c",
478 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
479 == 3)
480 && (sscanf (argv[2], "%d:%d:%d%c",
481 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
482 == 3))
484 tm.tm_year -= TM_YEAR_BASE;
485 tm.tm_mon--;
486 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
487 tmk = tm;
488 tl = mktime (&tmk);
489 lt = localtime (&tl);
490 if (lt)
492 tml = *lt;
493 lt = &tml;
495 printf ("mktime returns %ld == ", (long) tl);
496 print_tm (&tmk);
497 printf ("\n");
498 status = check_result (tl, tmk, tl, lt);
500 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
502 time_t from = atol (argv[1]);
503 time_t by = atol (argv[2]);
504 time_t to = atol (argv[3]);
506 if (argc == 4)
507 for (tl = from; tl <= to; tl += by)
509 lt = localtime (&tl);
510 if (lt)
512 tmk = tml = *lt;
513 tk = mktime (&tmk);
514 status |= check_result (tk, tmk, tl, tml);
516 else
518 printf ("localtime (%ld) yields 0\n", (long) tl);
519 status = 1;
522 else
523 for (tl = from; tl <= to; tl += by)
525 /* Null benchmark. */
526 lt = localtime (&tl);
527 if (lt)
529 tmk = tml = *lt;
530 tk = tl;
531 status |= check_result (tk, tmk, tl, tml);
533 else
535 printf ("localtime (%ld) yields 0\n", (long) tl);
536 status = 1;
540 else
541 printf ("Usage:\
542 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
543 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
544 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
545 argv[0], argv[0], argv[0]);
547 return status;
550 #endif /* DEBUG */
553 Local Variables:
554 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
555 End: