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[emacs.git] / src / mktime.c
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1 /* Convert a `struct tm' to a time_t value.
2 Copyright (C) 1993, 94, 95, 96, 97, 98, 99 Free Software Foundation, Inc.
3 Contributed by Paul Eggert (eggert@twinsun.com).
5 NOTE: The canonical source of this file is maintained with the GNU C Library.
6 Bugs can be reported to bug-glibc@gnu.org.
8 This program is free software; you can redistribute it and/or modify it
9 under the terms of the GNU General Public License as published by the
10 Free Software Foundation; either version 2, or (at your option) any
11 later version.
13 This program is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
18 You should have received a copy of the GNU General Public License
19 along with this program; if not, write to the Free Software
20 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
21 USA. */
23 /* Define this to have a standalone program to test this implementation of
24 mktime. */
25 /* #define DEBUG 1 */
27 #ifdef HAVE_CONFIG_H
28 # include <config.h>
29 #endif
31 #ifdef _LIBC
32 # define HAVE_LIMITS_H 1
33 # define STDC_HEADERS 1
34 #endif
36 /* Assume that leap seconds are possible, unless told otherwise.
37 If the host has a `zic' command with a `-L leapsecondfilename' option,
38 then it supports leap seconds; otherwise it probably doesn't. */
39 #ifndef LEAP_SECONDS_POSSIBLE
40 # define LEAP_SECONDS_POSSIBLE 1
41 #endif
43 #include <sys/types.h> /* Some systems define `time_t' here. */
44 #include <time.h>
46 #if HAVE_LIMITS_H
47 # include <limits.h>
48 #endif
50 #if DEBUG
51 # include <stdio.h>
52 # if STDC_HEADERS
53 # include <stdlib.h>
54 # endif
55 /* Make it work even if the system's libc has its own mktime routine. */
56 # define mktime my_mktime
57 #endif /* DEBUG */
59 #ifndef __P
60 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
61 # define __P(args) args
62 # else
63 # define __P(args) ()
64 # endif /* GCC. */
65 #endif /* Not __P. */
67 #ifndef CHAR_BIT
68 # define CHAR_BIT 8
69 #endif
71 /* The extra casts work around common compiler bugs. */
72 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
73 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
74 It is necessary at least when t == time_t. */
75 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
76 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
77 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
79 #ifndef INT_MIN
80 # define INT_MIN TYPE_MINIMUM (int)
81 #endif
82 #ifndef INT_MAX
83 # define INT_MAX TYPE_MAXIMUM (int)
84 #endif
86 #ifndef TIME_T_MIN
87 # define TIME_T_MIN TYPE_MINIMUM (time_t)
88 #endif
89 #ifndef TIME_T_MAX
90 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
91 #endif
93 #define TM_YEAR_BASE 1900
94 #define EPOCH_YEAR 1970
96 #ifndef __isleap
97 /* Nonzero if YEAR is a leap year (every 4 years,
98 except every 100th isn't, and every 400th is). */
99 # define __isleap(year) \
100 ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
101 #endif
103 /* How many days come before each month (0-12). */
104 const unsigned short int __mon_yday[2][13] =
106 /* Normal years. */
107 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
108 /* Leap years. */
109 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
113 #ifdef _LIBC
114 # define my_mktime_localtime_r __localtime_r
115 #else
116 /* If we're a mktime substitute in a GNU program, then prefer
117 localtime to localtime_r, since many localtime_r implementations
118 are buggy. */
119 static struct tm *
120 my_mktime_localtime_r (t, tp)
121 const time_t *t;
122 struct tm *tp;
124 struct tm *l = localtime (t);
125 if (! l)
126 return 0;
127 *tp = *l;
128 return tp;
130 #endif /* ! _LIBC */
133 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
134 measured in seconds, ignoring leap seconds.
135 YEAR uses the same numbering as TM->tm_year.
136 All values are in range, except possibly YEAR.
137 If TP is null, return a nonzero value.
138 If overflow occurs, yield the low order bits of the correct answer. */
139 static time_t
140 ydhms_tm_diff (year, yday, hour, min, sec, tp)
141 int year, yday, hour, min, sec;
142 const struct tm *tp;
144 if (!tp)
145 return 1;
146 else
148 /* Compute intervening leap days correctly even if year is negative.
149 Take care to avoid int overflow. time_t overflow is OK, since
150 only the low order bits of the correct time_t answer are needed.
151 Don't convert to time_t until after all divisions are done, since
152 time_t might be unsigned. */
153 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
154 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
155 int a100 = a4 / 25 - (a4 % 25 < 0);
156 int b100 = b4 / 25 - (b4 % 25 < 0);
157 int a400 = a100 >> 2;
158 int b400 = b100 >> 2;
159 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
160 time_t years = year - (time_t) tp->tm_year;
161 time_t days = (365 * years + intervening_leap_days
162 + (yday - tp->tm_yday));
163 return (60 * (60 * (24 * days + (hour - tp->tm_hour))
164 + (min - tp->tm_min))
165 + (sec - tp->tm_sec));
169 /* Use CONVERT to convert *T to a broken down time in *TP.
170 If *T is out of range for conversion, adjust it so that
171 it is the nearest in-range value and then convert that. */
172 static struct tm *
173 ranged_convert (convert, t, tp)
174 #ifdef PROTOTYPES
175 struct tm *(*convert) (const time_t *, struct tm *);
176 #else
177 struct tm *(*convert)();
178 #endif
179 time_t *t;
180 struct tm *tp;
182 struct tm *r;
184 if (! (r = (*convert) (t, tp)) && *t)
186 time_t bad = *t;
187 time_t ok = 0;
188 struct tm tm;
190 /* BAD is a known unconvertible time_t, and OK is a known good one.
191 Use binary search to narrow the range between BAD and OK until
192 they differ by 1. */
193 while (bad != ok + (bad < 0 ? -1 : 1))
195 time_t mid = *t = (bad < 0
196 ? bad + ((ok - bad) >> 1)
197 : ok + ((bad - ok) >> 1));
198 if ((r = (*convert) (t, tp)))
200 tm = *r;
201 ok = mid;
203 else
204 bad = mid;
207 if (!r && ok)
209 /* The last conversion attempt failed;
210 revert to the most recent successful attempt. */
211 *t = ok;
212 *tp = tm;
213 r = tp;
217 return r;
221 /* Convert *TP to a time_t value, inverting
222 the monotonic and mostly-unit-linear conversion function CONVERT.
223 Use *OFFSET to keep track of a guess at the offset of the result,
224 compared to what the result would be for UTC without leap seconds.
225 If *OFFSET's guess is correct, only one CONVERT call is needed. */
226 time_t
227 __mktime_internal (tp, convert, offset)
228 struct tm *tp;
229 #ifdef PROTOTYPES
230 struct tm *(*convert) (const time_t *, struct tm *);
231 #else
232 struct tm *(*convert)();
233 #endif
234 time_t *offset;
236 time_t t, dt, t0, t1, t2;
237 struct tm tm;
239 /* The maximum number of probes (calls to CONVERT) should be enough
240 to handle any combinations of time zone rule changes, solar time,
241 leap seconds, and oscillations around a spring-forward gap.
242 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
243 int remaining_probes = 6;
245 /* Time requested. Copy it in case CONVERT modifies *TP; this can
246 occur if TP is localtime's returned value and CONVERT is localtime. */
247 int sec = tp->tm_sec;
248 int min = tp->tm_min;
249 int hour = tp->tm_hour;
250 int mday = tp->tm_mday;
251 int mon = tp->tm_mon;
252 int year_requested = tp->tm_year;
253 int isdst = tp->tm_isdst;
255 /* Ensure that mon is in range, and set year accordingly. */
256 int mon_remainder = mon % 12;
257 int negative_mon_remainder = mon_remainder < 0;
258 int mon_years = mon / 12 - negative_mon_remainder;
259 int year = year_requested + mon_years;
261 /* The other values need not be in range:
262 the remaining code handles minor overflows correctly,
263 assuming int and time_t arithmetic wraps around.
264 Major overflows are caught at the end. */
266 /* Calculate day of year from year, month, and day of month.
267 The result need not be in range. */
268 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
269 [mon_remainder + 12 * negative_mon_remainder])
270 + mday - 1);
272 int sec_requested = sec;
273 #if LEAP_SECONDS_POSSIBLE
274 /* Handle out-of-range seconds specially,
275 since ydhms_tm_diff assumes every minute has 60 seconds. */
276 if (sec < 0)
277 sec = 0;
278 if (59 < sec)
279 sec = 59;
280 #endif
282 /* Invert CONVERT by probing. First assume the same offset as last time.
283 Then repeatedly use the error to improve the guess. */
285 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
286 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
287 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
289 for (t = t1 = t2 = t0 + *offset;
290 (dt = ydhms_tm_diff (year, yday, hour, min, sec,
291 ranged_convert (convert, &t, &tm)));
292 t1 = t2, t2 = t, t += dt)
293 if (t == t1 && t != t2
294 && (isdst < 0 || tm.tm_isdst < 0
295 || (isdst != 0) != (tm.tm_isdst != 0)))
296 /* We can't possibly find a match, as we are oscillating
297 between two values. The requested time probably falls
298 within a spring-forward gap of size DT. Follow the common
299 practice in this case, which is to return a time that is DT
300 away from the requested time, preferring a time whose
301 tm_isdst differs from the requested value. In practice,
302 this is more useful than returning -1. */
303 break;
304 else if (--remaining_probes == 0)
305 return -1;
307 /* If we have a match, check whether tm.tm_isdst has the requested
308 value, if any. */
309 if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
311 /* tm.tm_isdst has the wrong value. Look for a neighboring
312 time with the right value, and use its UTC offset.
313 Heuristic: probe the previous three calendar quarters (approximately),
314 looking for the desired isdst. This isn't perfect,
315 but it's good enough in practice. */
316 int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
317 int i;
319 /* If we're too close to the time_t limit, look in future quarters. */
320 if (t < TIME_T_MIN + 3 * quarter)
321 quarter = -quarter;
323 for (i = 1; i <= 3; i++)
325 time_t ot = t - i * quarter;
326 struct tm otm;
327 ranged_convert (convert, &ot, &otm);
328 if (otm.tm_isdst == isdst)
330 /* We found the desired tm_isdst.
331 Extrapolate back to the desired time. */
332 t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
333 ranged_convert (convert, &t, &tm);
334 break;
339 *offset = t - t0;
341 #if LEAP_SECONDS_POSSIBLE
342 if (sec_requested != tm.tm_sec)
344 /* Adjust time to reflect the tm_sec requested, not the normalized value.
345 Also, repair any damage from a false match due to a leap second. */
346 t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
347 if (! (*convert) (&t, &tm))
348 return -1;
350 #endif
352 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
354 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
355 so check for major overflows. A gross check suffices,
356 since if t has overflowed, it is off by a multiple of
357 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
358 the difference that is bounded by a small value. */
360 double dyear = (double) year_requested + mon_years - tm.tm_year;
361 double dday = 366 * dyear + mday;
362 double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
364 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
365 correct results, ie., it erroneously gives a positive value
366 of 715827882. Setting a variable first then doing math on it
367 seems to work. (ghazi@caip.rutgers.edu) */
369 const time_t time_t_max = TIME_T_MAX;
370 const time_t time_t_min = TIME_T_MIN;
372 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
373 return -1;
376 *tp = tm;
377 return t;
381 static time_t localtime_offset;
383 /* Convert *TP to a time_t value. */
384 time_t
385 mktime (tp)
386 struct tm *tp;
388 #ifdef _LIBC
389 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
390 time zone names contained in the external variable `tzname' shall
391 be set as if the tzset() function had been called. */
392 __tzset ();
393 #endif
395 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
398 #ifdef weak_alias
399 weak_alias (mktime, timelocal)
400 #endif
402 #if DEBUG
404 static int
405 not_equal_tm (a, b)
406 struct tm *a;
407 struct tm *b;
409 return ((a->tm_sec ^ b->tm_sec)
410 | (a->tm_min ^ b->tm_min)
411 | (a->tm_hour ^ b->tm_hour)
412 | (a->tm_mday ^ b->tm_mday)
413 | (a->tm_mon ^ b->tm_mon)
414 | (a->tm_year ^ b->tm_year)
415 | (a->tm_mday ^ b->tm_mday)
416 | (a->tm_yday ^ b->tm_yday)
417 | (a->tm_isdst ^ b->tm_isdst));
420 static void
421 print_tm (tp)
422 struct tm *tp;
424 if (tp)
425 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
426 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
427 tp->tm_hour, tp->tm_min, tp->tm_sec,
428 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
429 else
430 printf ("0");
433 static int
434 check_result (tk, tmk, tl, lt)
435 time_t tk;
436 struct tm tmk;
437 time_t tl;
438 struct tm *lt;
440 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
442 printf ("mktime (");
443 print_tm (&tmk);
444 printf (")\nyields (");
445 print_tm (lt);
446 printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
447 return 1;
450 return 0;
454 main (argc, argv)
455 int argc;
456 char **argv;
458 int status = 0;
459 struct tm tm, tmk, tml;
460 struct tm *lt;
461 time_t tk, tl;
462 char trailer;
464 if ((argc == 3 || argc == 4)
465 && (sscanf (argv[1], "%d-%d-%d%c",
466 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
467 == 3)
468 && (sscanf (argv[2], "%d:%d:%d%c",
469 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
470 == 3))
472 tm.tm_year -= TM_YEAR_BASE;
473 tm.tm_mon--;
474 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
475 tmk = tm;
476 tl = mktime (&tmk);
477 lt = localtime (&tl);
478 if (lt)
480 tml = *lt;
481 lt = &tml;
483 printf ("mktime returns %ld == ", (long) tl);
484 print_tm (&tmk);
485 printf ("\n");
486 status = check_result (tl, tmk, tl, lt);
488 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
490 time_t from = atol (argv[1]);
491 time_t by = atol (argv[2]);
492 time_t to = atol (argv[3]);
494 if (argc == 4)
495 for (tl = from; tl <= to; tl += by)
497 lt = localtime (&tl);
498 if (lt)
500 tmk = tml = *lt;
501 tk = mktime (&tmk);
502 status |= check_result (tk, tmk, tl, tml);
504 else
506 printf ("localtime (%ld) yields 0\n", (long) tl);
507 status = 1;
510 else
511 for (tl = from; tl <= to; tl += by)
513 /* Null benchmark. */
514 lt = localtime (&tl);
515 if (lt)
517 tmk = tml = *lt;
518 tk = tl;
519 status |= check_result (tk, tmk, tl, tml);
521 else
523 printf ("localtime (%ld) yields 0\n", (long) tl);
524 status = 1;
528 else
529 printf ("Usage:\
530 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
531 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
532 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
533 argv[0], argv[0], argv[0]);
535 return status;
538 #endif /* DEBUG */
541 Local Variables:
542 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
543 End: