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[findutils.git] / lib / 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 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 Library General Public License as
8 published by the Free Software Foundation; either version 2 of the
9 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 Library General Public License for more details.
16 You should have received a copy of the GNU Library General Public
17 License along with the GNU C Library; see the file COPYING.LIB. If not,
18 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 Boston, MA 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 # endif
53 /* Make it work even if the system's libc has its own mktime routine. */
54 # define mktime my_mktime
55 #endif /* DEBUG */
57 #ifndef __P
58 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
59 # define __P(args) args
60 # else
61 # define __P(args) ()
62 # endif /* GCC. */
63 #endif /* Not __P. */
65 #ifndef CHAR_BIT
66 # define CHAR_BIT 8
67 #endif
69 /* The extra casts work around common compiler bugs. */
70 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
71 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
72 It is necessary at least when t == time_t. */
73 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
74 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
75 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
77 #ifndef INT_MIN
78 # define INT_MIN TYPE_MINIMUM (int)
79 #endif
80 #ifndef INT_MAX
81 # define INT_MAX TYPE_MAXIMUM (int)
82 #endif
84 #ifndef TIME_T_MIN
85 # define TIME_T_MIN TYPE_MINIMUM (time_t)
86 #endif
87 #ifndef TIME_T_MAX
88 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
89 #endif
91 #define TM_YEAR_BASE 1900
92 #define EPOCH_YEAR 1970
94 #ifndef __isleap
95 /* Nonzero if YEAR is a leap year (every 4 years,
96 except every 100th isn't, and every 400th is). */
97 # define __isleap(year) \
98 ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
99 #endif
101 /* How many days come before each month (0-12). */
102 const unsigned short int __mon_yday[2][13] =
104 /* Normal years. */
105 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
106 /* Leap years. */
107 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
111 #ifdef _LIBC
112 # define my_mktime_localtime_r __localtime_r
113 #else
114 /* If we're a mktime substitute in a GNU program, then prefer
115 localtime to localtime_r, since many localtime_r implementations
116 are buggy. */
117 static struct tm *
118 my_mktime_localtime_r (const time_t *t, struct tm *tp)
120 struct tm *l = localtime (t);
121 if (! l)
122 return 0;
123 *tp = *l;
124 return tp;
126 #endif /* ! _LIBC */
129 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
130 measured in seconds, ignoring leap seconds.
131 YEAR uses the same numbering as TM->tm_year.
132 All values are in range, except possibly YEAR.
133 If TP is null, return a nonzero value.
134 If overflow occurs, yield the low order bits of the correct answer. */
135 static time_t
136 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
137 const struct tm *tp)
139 if (!tp)
140 return 1;
141 else
143 /* Compute intervening leap days correctly even if year is negative.
144 Take care to avoid int overflow. time_t overflow is OK, since
145 only the low order bits of the correct time_t answer are needed.
146 Don't convert to time_t until after all divisions are done, since
147 time_t might be unsigned. */
148 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
149 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
150 int a100 = a4 / 25 - (a4 % 25 < 0);
151 int b100 = b4 / 25 - (b4 % 25 < 0);
152 int a400 = a100 >> 2;
153 int b400 = b100 >> 2;
154 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
155 time_t years = year - (time_t) tp->tm_year;
156 time_t days = (365 * years + intervening_leap_days
157 + (yday - tp->tm_yday));
158 return (60 * (60 * (24 * days + (hour - tp->tm_hour))
159 + (min - tp->tm_min))
160 + (sec - tp->tm_sec));
164 /* Use CONVERT to convert *T to a broken down time in *TP.
165 If *T is out of range for conversion, adjust it so that
166 it is the nearest in-range value and then convert that. */
167 static struct tm *
168 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
169 time_t *t, struct tm *tp)
171 struct tm *r;
173 if (! (r = (*convert) (t, tp)) && *t)
175 time_t bad = *t;
176 time_t ok = 0;
177 struct tm tm;
179 /* BAD is a known unconvertible time_t, and OK is a known good one.
180 Use binary search to narrow the range between BAD and OK until
181 they differ by 1. */
182 while (bad != ok + (bad < 0 ? -1 : 1))
184 time_t mid = *t = (bad < 0
185 ? bad + ((ok - bad) >> 1)
186 : ok + ((bad - ok) >> 1));
187 if ((r = (*convert) (t, tp)))
189 tm = *r;
190 ok = mid;
192 else
193 bad = mid;
196 if (!r && ok)
198 /* The last conversion attempt failed;
199 revert to the most recent successful attempt. */
200 *t = ok;
201 *tp = tm;
202 r = tp;
206 return r;
210 /* Convert *TP to a time_t value, inverting
211 the monotonic and mostly-unit-linear conversion function CONVERT.
212 Use *OFFSET to keep track of a guess at the offset of the result,
213 compared to what the result would be for UTC without leap seconds.
214 If *OFFSET's guess is correct, only one CONVERT call is needed. */
215 time_t
216 __mktime_internal (struct tm *tp,
217 struct tm *(*convert) (const time_t *, struct tm *),
218 time_t *offset)
220 time_t t, dt, t0, t1, t2;
221 struct tm tm;
223 /* The maximum number of probes (calls to CONVERT) should be enough
224 to handle any combinations of time zone rule changes, solar time,
225 leap seconds, and oscillations around a spring-forward gap.
226 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
227 int remaining_probes = 6;
229 /* Time requested. Copy it in case CONVERT modifies *TP; this can
230 occur if TP is localtime's returned value and CONVERT is localtime. */
231 int sec = tp->tm_sec;
232 int min = tp->tm_min;
233 int hour = tp->tm_hour;
234 int mday = tp->tm_mday;
235 int mon = tp->tm_mon;
236 int year_requested = tp->tm_year;
237 int isdst = tp->tm_isdst;
239 /* Ensure that mon is in range, and set year accordingly. */
240 int mon_remainder = mon % 12;
241 int negative_mon_remainder = mon_remainder < 0;
242 int mon_years = mon / 12 - negative_mon_remainder;
243 int year = year_requested + mon_years;
245 /* The other values need not be in range:
246 the remaining code handles minor overflows correctly,
247 assuming int and time_t arithmetic wraps around.
248 Major overflows are caught at the end. */
250 /* Calculate day of year from year, month, and day of month.
251 The result need not be in range. */
252 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
253 [mon_remainder + 12 * negative_mon_remainder])
254 + mday - 1);
256 int sec_requested = sec;
257 #if LEAP_SECONDS_POSSIBLE
258 /* Handle out-of-range seconds specially,
259 since ydhms_tm_diff assumes every minute has 60 seconds. */
260 if (sec < 0)
261 sec = 0;
262 if (59 < sec)
263 sec = 59;
264 #endif
266 /* Invert CONVERT by probing. First assume the same offset as last time.
267 Then repeatedly use the error to improve the guess. */
269 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
270 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
271 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
273 for (t = t1 = t2 = t0 + *offset;
274 (dt = ydhms_tm_diff (year, yday, hour, min, sec,
275 ranged_convert (convert, &t, &tm)));
276 t1 = t2, t2 = t, t += dt)
277 if (t == t1 && t != t2
278 && (isdst < 0 || 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. In practice,
286 this is more useful than returning -1. */
287 break;
288 else if (--remaining_probes == 0)
289 return -1;
291 /* If we have a match, check whether tm.tm_isdst has the requested
292 value, if any. */
293 if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
295 /* tm.tm_isdst has the wrong value. Look for a neighboring
296 time with the right value, and use its UTC offset.
297 Heuristic: probe the previous three calendar quarters (approximately),
298 looking for the desired isdst. This isn't perfect,
299 but it's good enough in practice. */
300 int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
301 int i;
303 /* If we're too close to the time_t limit, look in future quarters. */
304 if (t < TIME_T_MIN + 3 * quarter)
305 quarter = -quarter;
307 for (i = 1; i <= 3; i++)
309 time_t ot = t - i * quarter;
310 struct tm otm;
311 ranged_convert (convert, &ot, &otm);
312 if (otm.tm_isdst == isdst)
314 /* We found the desired tm_isdst.
315 Extrapolate back to the desired time. */
316 t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
317 ranged_convert (convert, &t, &tm);
318 break;
323 *offset = t - t0;
325 #if LEAP_SECONDS_POSSIBLE
326 if (sec_requested != tm.tm_sec)
328 /* Adjust time to reflect the tm_sec requested, not the normalized value.
329 Also, repair any damage from a false match due to a leap second. */
330 t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
331 if (! (*convert) (&t, &tm))
332 return -1;
334 #endif
336 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
338 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
339 so check for major overflows. A gross check suffices,
340 since if t has overflowed, it is off by a multiple of
341 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
342 the difference that is bounded by a small value. */
344 double dyear = (double) year_requested + mon_years - tm.tm_year;
345 double dday = 366 * dyear + mday;
346 double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
348 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
349 correct results, ie., it erroneously gives a positive value
350 of 715827882. Setting a variable first then doing math on it
351 seems to work. (ghazi@caip.rutgers.edu) */
353 const time_t time_t_max = TIME_T_MAX;
354 const time_t time_t_min = TIME_T_MIN;
356 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
357 return -1;
360 *tp = tm;
361 return t;
365 static time_t localtime_offset;
367 /* Convert *TP to a time_t value. */
368 time_t
369 mktime (tp)
370 struct tm *tp;
372 #ifdef _LIBC
373 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
374 time zone names contained in the external variable `tzname' shall
375 be set as if the tzset() function had been called. */
376 __tzset ();
377 #endif
379 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
382 #ifdef weak_alias
383 weak_alias (mktime, timelocal)
384 #endif
386 #if DEBUG
388 static int
389 not_equal_tm (a, b)
390 struct tm *a;
391 struct tm *b;
393 return ((a->tm_sec ^ b->tm_sec)
394 | (a->tm_min ^ b->tm_min)
395 | (a->tm_hour ^ b->tm_hour)
396 | (a->tm_mday ^ b->tm_mday)
397 | (a->tm_mon ^ b->tm_mon)
398 | (a->tm_year ^ b->tm_year)
399 | (a->tm_mday ^ b->tm_mday)
400 | (a->tm_yday ^ b->tm_yday)
401 | (a->tm_isdst ^ b->tm_isdst));
404 static void
405 print_tm (tp)
406 struct tm *tp;
408 if (tp)
409 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
410 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
411 tp->tm_hour, tp->tm_min, tp->tm_sec,
412 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
413 else
414 printf ("0");
417 static int
418 check_result (tk, tmk, tl, lt)
419 time_t tk;
420 struct tm tmk;
421 time_t tl;
422 struct tm *lt;
424 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
426 printf ("mktime (");
427 print_tm (&tmk);
428 printf (")\nyields (");
429 print_tm (lt);
430 printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
431 return 1;
434 return 0;
438 main (argc, argv)
439 int argc;
440 char **argv;
442 int status = 0;
443 struct tm tm, tmk, tml;
444 struct tm *lt;
445 time_t tk, tl;
446 char trailer;
448 if ((argc == 3 || argc == 4)
449 && (sscanf (argv[1], "%d-%d-%d%c",
450 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
451 == 3)
452 && (sscanf (argv[2], "%d:%d:%d%c",
453 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
454 == 3))
456 tm.tm_year -= TM_YEAR_BASE;
457 tm.tm_mon--;
458 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
459 tmk = tm;
460 tl = mktime (&tmk);
461 lt = localtime (&tl);
462 if (lt)
464 tml = *lt;
465 lt = &tml;
467 printf ("mktime returns %ld == ", (long) tl);
468 print_tm (&tmk);
469 printf ("\n");
470 status = check_result (tl, tmk, tl, lt);
472 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
474 time_t from = atol (argv[1]);
475 time_t by = atol (argv[2]);
476 time_t to = atol (argv[3]);
478 if (argc == 4)
479 for (tl = from; tl <= to; tl += by)
481 lt = localtime (&tl);
482 if (lt)
484 tmk = tml = *lt;
485 tk = mktime (&tmk);
486 status |= check_result (tk, tmk, tl, tml);
488 else
490 printf ("localtime (%ld) yields 0\n", (long) tl);
491 status = 1;
494 else
495 for (tl = from; tl <= to; tl += by)
497 /* Null benchmark. */
498 lt = localtime (&tl);
499 if (lt)
501 tmk = tml = *lt;
502 tk = tl;
503 status |= check_result (tk, tmk, tl, tml);
505 else
507 printf ("localtime (%ld) yields 0\n", (long) tl);
508 status = 1;
512 else
513 printf ("Usage:\
514 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
515 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
516 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
517 argv[0], argv[0], argv[0]);
519 return status;
522 #endif /* DEBUG */
525 Local Variables:
526 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
527 End: