1 /* mktime: convert a `struct tm' to a time_t value
2 Copyright (C) 1993-1997, 1998 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@prep.ai.mit.edu.
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
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,
23 /* Define this to have a standalone program to test this implementation of
32 # define HAVE_LIMITS_H 1
33 # define STDC_HEADERS 1
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
43 #include <sys/types.h> /* Some systems define `time_t' here. */
55 /* Make it work even if the system's libc has its own mktime routine. */
56 # define mktime my_mktime
60 # if defined (__GNUC__) || (defined (__STDC__) && __STDC__)
61 # define __P(args) args
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)))
80 # define INT_MIN TYPE_MINIMUM (int)
83 # define INT_MAX TYPE_MAXIMUM (int)
87 # define TIME_T_MIN TYPE_MINIMUM (time_t)
90 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
93 #define TM_YEAR_BASE 1900
94 #define EPOCH_YEAR 1970
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))
103 /* How many days come before each month (0-12). */
104 const unsigned short int __mon_yday[2][13] =
107 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
109 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
112 static struct tm *ranged_convert __P ((struct tm *(*) __P ((const time_t *,
114 time_t *, struct tm *));
115 static time_t ydhms_tm_diff __P ((int, int, int, int, int, const struct tm *));
116 time_t __mktime_internal __P ((struct tm *,
117 struct tm *(*) (const time_t *, struct tm *),
122 # define my_mktime_localtime_r __localtime_r
124 /* If we're a mktime substitute in a GNU program, then prefer
125 localtime to localtime_r, since many localtime_r implementations
127 static struct tm *my_mktime_localtime_r __P ((const time_t *, struct tm *));
129 my_mktime_localtime_r (const time_t *t, struct tm *tp)
131 struct tm *l = localtime (t);
140 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
141 measured in seconds, ignoring leap seconds.
142 YEAR uses the same numbering as TM->tm_year.
143 All values are in range, except possibly YEAR.
144 If TP is null, return a nonzero value.
145 If overflow occurs, yield the low order bits of the correct answer. */
147 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
154 /* Compute intervening leap days correctly even if year is negative.
155 Take care to avoid int overflow. time_t overflow is OK, since
156 only the low order bits of the correct time_t answer are needed.
157 Don't convert to time_t until after all divisions are done, since
158 time_t might be unsigned. */
159 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
160 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
161 int a100 = a4 / 25 - (a4 % 25 < 0);
162 int b100 = b4 / 25 - (b4 % 25 < 0);
163 int a400 = a100 >> 2;
164 int b400 = b100 >> 2;
165 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
166 time_t years = year - (time_t) tp->tm_year;
167 time_t days = (365 * years + intervening_leap_days
168 + (yday - tp->tm_yday));
169 return (60 * (60 * (24 * days + (hour - tp->tm_hour))
170 + (min - tp->tm_min))
171 + (sec - tp->tm_sec));
176 static time_t localtime_offset;
178 /* Convert *TP to a time_t value. */
180 mktime (struct tm *tp)
183 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
184 time zone names contained in the external variable `tzname' shall
185 be set as if the tzset() function had been called. */
189 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
192 /* Use CONVERT to convert *T to a broken down time in *TP.
193 If *T is out of range for conversion, adjust it so that
194 it is the nearest in-range value and then convert that. */
196 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
197 time_t *t, struct tm *tp)
201 if (! (r = (*convert) (t, tp)) && *t)
207 /* BAD is a known unconvertible time_t, and OK is a known good one.
208 Use binary search to narrow the range between BAD and OK until
210 while (bad != ok + (bad < 0 ? -1 : 1))
212 time_t mid = *t = (bad < 0
213 ? bad + ((ok - bad) >> 1)
214 : ok + ((bad - ok) >> 1));
215 if ((r = (*convert) (t, tp)))
226 /* The last conversion attempt failed;
227 revert to the most recent successful attempt. */
238 /* Convert *TP to a time_t value, inverting
239 the monotonic and mostly-unit-linear conversion function CONVERT.
240 Use *OFFSET to keep track of a guess at the offset of the result,
241 compared to what the result would be for UTC without leap seconds.
242 If *OFFSET's guess is correct, only one CONVERT call is needed. */
244 __mktime_internal (struct tm *tp,
245 struct tm *(*convert) (const time_t *, struct tm *),
248 time_t t, dt, t0, t1, t2;
251 /* The maximum number of probes (calls to CONVERT) should be enough
252 to handle any combinations of time zone rule changes, solar time,
253 leap seconds, and oscillations around a spring-forward gap.
254 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
255 int remaining_probes = 6;
257 /* Time requested. Copy it in case CONVERT modifies *TP; this can
258 occur if TP is localtime's returned value and CONVERT is localtime. */
259 int sec = tp->tm_sec;
260 int min = tp->tm_min;
261 int hour = tp->tm_hour;
262 int mday = tp->tm_mday;
263 int mon = tp->tm_mon;
264 int year_requested = tp->tm_year;
265 int isdst = tp->tm_isdst;
267 /* Ensure that mon is in range, and set year accordingly. */
268 int mon_remainder = mon % 12;
269 int negative_mon_remainder = mon_remainder < 0;
270 int mon_years = mon / 12 - negative_mon_remainder;
271 int year = year_requested + mon_years;
273 /* The other values need not be in range:
274 the remaining code handles minor overflows correctly,
275 assuming int and time_t arithmetic wraps around.
276 Major overflows are caught at the end. */
278 /* Calculate day of year from year, month, and day of month.
279 The result need not be in range. */
280 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
281 [mon_remainder + 12 * negative_mon_remainder])
284 int sec_requested = sec;
285 #if LEAP_SECONDS_POSSIBLE
286 /* Handle out-of-range seconds specially,
287 since ydhms_tm_diff assumes every minute has 60 seconds. */
294 /* Invert CONVERT by probing. First assume the same offset as last time.
295 Then repeatedly use the error to improve the guess. */
297 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
298 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
299 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
301 for (t = t1 = t2 = t0 + *offset;
302 (dt = ydhms_tm_diff (year, yday, hour, min, sec,
303 ranged_convert (convert, &t, &tm)));
304 t1 = t2, t2 = t, t += dt)
305 if (t == t1 && t != t2
306 && (isdst < 0 || tm.tm_isdst < 0
307 || (isdst != 0) != (tm.tm_isdst != 0)))
308 /* We can't possibly find a match, as we are oscillating
309 between two values. The requested time probably falls
310 within a spring-forward gap of size DT. Follow the common
311 practice in this case, which is to return a time that is DT
312 away from the requested time, preferring a time whose
313 tm_isdst differs from the requested value. In practice,
314 this is more useful than returning -1. */
316 else if (--remaining_probes == 0)
319 /* If we have a match, check whether tm.tm_isdst has the requested
321 if (dt == 0 && 0 <= isdst && 0 <= tm.tm_isdst)
323 int dst_diff = (isdst != 0) - (tm.tm_isdst != 0);
326 /* Move two hours in the direction indicated by the disagreement,
327 probe some more, and switch to a new time if found.
328 The largest known fallback due to daylight savings is two hours:
329 once, in Newfoundland, 1988-10-30 02:00 -> 00:00. */
330 time_t ot = t - 2 * 60 * 60 * dst_diff;
331 while (--remaining_probes != 0)
334 if (! (dt = ydhms_tm_diff (year, yday, hour, min, sec,
335 ranged_convert (convert, &ot, &otm))))
342 break; /* Avoid a redundant probe. */
349 #if LEAP_SECONDS_POSSIBLE
350 if (sec_requested != tm.tm_sec)
352 /* Adjust time to reflect the tm_sec requested, not the normalized value.
353 Also, repair any damage from a false match due to a leap second. */
354 t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
355 if (! (*convert) (&t, &tm))
360 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
362 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
363 so check for major overflows. A gross check suffices,
364 since if t has overflowed, it is off by a multiple of
365 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
366 the difference that is bounded by a small value. */
368 double dyear = (double) year_requested + mon_years - tm.tm_year;
369 double dday = 366 * dyear + mday;
370 double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
372 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
373 correct results, ie., it erroneously gives a positive value
374 of 715827882. Setting a variable first then doing math on it
375 seems to work. (ghazi@caip.rutgers.edu) */
377 const time_t time_t_max = TIME_T_MAX;
378 const time_t time_t_min = TIME_T_MIN;
380 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
389 weak_alias (mktime, timelocal)
399 return ((a->tm_sec ^ b->tm_sec)
400 | (a->tm_min ^ b->tm_min)
401 | (a->tm_hour ^ b->tm_hour)
402 | (a->tm_mday ^ b->tm_mday)
403 | (a->tm_mon ^ b->tm_mon)
404 | (a->tm_year ^ b->tm_year)
405 | (a->tm_mday ^ b->tm_mday)
406 | (a->tm_yday ^ b->tm_yday)
407 | (a->tm_isdst ^ b->tm_isdst));
415 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
416 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
417 tp->tm_hour, tp->tm_min, tp->tm_sec,
418 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
424 check_result (tk, tmk, tl, lt)
430 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
434 printf (")\nyields (");
436 printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
449 struct tm tm, tmk, tml;
454 if ((argc == 3 || argc == 4)
455 && (sscanf (argv[1], "%d-%d-%d%c",
456 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
458 && (sscanf (argv[2], "%d:%d:%d%c",
459 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
462 tm.tm_year -= TM_YEAR_BASE;
464 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
467 lt = localtime (&tl);
473 printf ("mktime returns %ld == ", (long) tl);
476 status = check_result (tl, tmk, tl, lt);
478 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
480 time_t from = atol (argv[1]);
481 time_t by = atol (argv[2]);
482 time_t to = atol (argv[3]);
485 for (tl = from; tl <= to; tl += by)
487 lt = localtime (&tl);
492 status |= check_result (tk, tmk, tl, tml);
496 printf ("localtime (%ld) yields 0\n", (long) tl);
501 for (tl = from; tl <= to; tl += by)
503 /* Null benchmark. */
504 lt = localtime (&tl);
509 status |= check_result (tk, tmk, tl, tml);
513 printf ("localtime (%ld) yields 0\n", (long) tl);
520 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
521 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
522 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
523 argv[0], argv[0], argv[0]);
532 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"