1 /* Convert a `struct tm' to a time_t value.
2 Copyright (C) 1993-1999, 2002, 2003 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Paul Eggert (eggert@twinsun.com).
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 This program 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
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License along
17 with this program; if not, write to the Free Software Foundation,
18 Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
20 /* Define this to have a standalone program to test this implementation of
29 # define STDC_HEADERS 1
32 /* Assume that leap seconds are possible, unless told otherwise.
33 If the host has a `zic' command with a `-L leapsecondfilename' option,
34 then it supports leap seconds; otherwise it probably doesn't. */
35 #ifndef LEAP_SECONDS_POSSIBLE
36 # define LEAP_SECONDS_POSSIBLE 1
39 #include <sys/types.h> /* Some systems define `time_t' here. */
50 /* Make it work even if the system's libc has its own mktime routine. */
51 # define mktime my_mktime
54 /* The extra casts work around common compiler bugs. */
55 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
56 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
57 It is necessary at least when t == time_t. */
58 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
59 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
60 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
63 # define TIME_T_MIN TYPE_MINIMUM (time_t)
66 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
69 #define TM_YEAR_BASE 1900
70 #define EPOCH_YEAR 1970
73 /* Nonzero if YEAR is a leap year (every 4 years,
74 except every 100th isn't, and every 400th is). */
75 # define __isleap(year) \
76 ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
79 /* How many days come before each month (0-12). */
83 const unsigned short int __mon_yday[2][13] =
86 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
88 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
93 # define my_mktime_localtime_r __localtime_r
95 /* If we're a mktime substitute in a GNU program, then prefer
96 localtime to localtime_r, since many localtime_r implementations
99 my_mktime_localtime_r (const time_t *t, struct tm *tp)
101 struct tm *l = localtime (t);
110 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
111 measured in seconds, ignoring leap seconds.
112 YEAR uses the same numbering as TM->tm_year.
113 All values are in range, except possibly YEAR.
114 If TP is null, return a nonzero value.
115 If overflow occurs, yield the low order bits of the correct answer. */
117 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
124 /* Compute intervening leap days correctly even if year is negative.
125 Take care to avoid int overflow. time_t overflow is OK, since
126 only the low order bits of the correct time_t answer are needed.
127 Don't convert to time_t until after all divisions are done, since
128 time_t might be unsigned. */
129 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
130 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
131 int a100 = a4 / 25 - (a4 % 25 < 0);
132 int b100 = b4 / 25 - (b4 % 25 < 0);
133 int a400 = a100 >> 2;
134 int b400 = b100 >> 2;
135 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
136 time_t years = year - (time_t) tp->tm_year;
137 time_t days = (365 * years + intervening_leap_days
138 + (yday - tp->tm_yday));
139 return (60 * (60 * (24 * days + (hour - tp->tm_hour))
140 + (min - tp->tm_min))
141 + (sec - tp->tm_sec));
145 /* Use CONVERT to convert *T to a broken down time in *TP.
146 If *T is out of range for conversion, adjust it so that
147 it is the nearest in-range value and then convert that. */
149 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
150 time_t *t, struct tm *tp)
154 if (! (r = (*convert) (t, tp)) && *t)
160 /* BAD is a known unconvertible time_t, and OK is a known good one.
161 Use binary search to narrow the range between BAD and OK until
163 while (bad != ok + (bad < 0 ? -1 : 1))
165 time_t mid = *t = (bad < 0
166 ? bad + ((ok - bad) >> 1)
167 : ok + ((bad - ok) >> 1));
168 if ((r = (*convert) (t, tp)))
179 /* The last conversion attempt failed;
180 revert to the most recent successful attempt. */
191 /* Convert *TP to a time_t value, inverting
192 the monotonic and mostly-unit-linear conversion function CONVERT.
193 Use *OFFSET to keep track of a guess at the offset of the result,
194 compared to what the result would be for UTC without leap seconds.
195 If *OFFSET's guess is correct, only one CONVERT call is needed. */
200 __mktime_internal (struct tm *tp,
201 struct tm *(*convert) (const time_t *, struct tm *),
204 time_t t, dt, t0, t1, t2;
207 /* The maximum number of probes (calls to CONVERT) should be enough
208 to handle any combinations of time zone rule changes, solar time,
209 leap seconds, and oscillations around a spring-forward gap.
210 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
211 int remaining_probes = 6;
213 /* Time requested. Copy it in case CONVERT modifies *TP; this can
214 occur if TP is localtime's returned value and CONVERT is localtime. */
215 int sec = tp->tm_sec;
216 int min = tp->tm_min;
217 int hour = tp->tm_hour;
218 int mday = tp->tm_mday;
219 int mon = tp->tm_mon;
220 int year_requested = tp->tm_year;
221 int isdst = tp->tm_isdst;
223 /* 1 if the previous probe was DST. */
226 /* Ensure that mon is in range, and set year accordingly. */
227 int mon_remainder = mon % 12;
228 int negative_mon_remainder = mon_remainder < 0;
229 int mon_years = mon / 12 - negative_mon_remainder;
230 int year = year_requested + mon_years;
232 /* The other values need not be in range:
233 the remaining code handles minor overflows correctly,
234 assuming int and time_t arithmetic wraps around.
235 Major overflows are caught at the end. */
237 /* Calculate day of year from year, month, and day of month.
238 The result need not be in range. */
239 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
240 [mon_remainder + 12 * negative_mon_remainder])
243 int sec_requested = sec;
245 #if LEAP_SECONDS_POSSIBLE
246 /* Handle out-of-range seconds specially,
247 since ydhms_tm_diff assumes every minute has 60 seconds. */
254 /* Invert CONVERT by probing. First assume the same offset as last time.
255 Then repeatedly use the error to improve the guess. */
257 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
258 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
259 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
261 if ((t < t0) != (*offset < 0))
264 for (t1 = t2 = t, dst2 = 0;
265 (dt = ydhms_tm_diff (year, yday, hour, min, sec,
266 ranged_convert (convert, &t, &tm)));
267 t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
268 if (t == t1 && t != t2
271 ? dst2 <= (tm.tm_isdst != 0)
272 : (isdst != 0) != (tm.tm_isdst != 0))))
273 /* We can't possibly find a match, as we are oscillating
274 between two values. The requested time probably falls
275 within a spring-forward gap of size DT. Follow the common
276 practice in this case, which is to return a time that is DT
277 away from the requested time, preferring a time whose
278 tm_isdst differs from the requested value. (If no tm_isdst
279 was requested and only one of the two values has a nonzero
280 tm_isdst, prefer that value.) In practice, this is more
281 useful than returning -1. */
283 else if (--remaining_probes == 0)
286 /* If we have a match, check whether tm.tm_isdst has the requested
288 if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
290 /* tm.tm_isdst has the wrong value. Look for a neighboring
291 time with the right value, and use its UTC offset.
292 Heuristic: probe the previous three calendar quarters (approximately),
293 looking for the desired isdst. This isn't perfect,
294 but it's good enough in practice. */
295 int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
298 /* If we're too close to the time_t limit, look in future quarters. */
299 if (t < TIME_T_MIN + 3 * quarter)
302 for (i = 1; i <= 3; i++)
304 time_t ot = t - i * quarter;
306 ranged_convert (convert, &ot, &otm);
307 if (otm.tm_isdst == isdst)
309 /* We found the desired tm_isdst.
310 Extrapolate back to the desired time. */
311 t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
312 ranged_convert (convert, &t, &tm);
320 #if LEAP_SECONDS_POSSIBLE
321 if (sec_requested != tm.tm_sec)
323 /* Adjust time to reflect the tm_sec requested, not the normalized value.
324 Also, repair any damage from a false match due to a leap second. */
325 t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
326 if (! (*convert) (&t, &tm))
331 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
333 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
334 so check for major overflows. A gross check suffices,
335 since if t has overflowed, it is off by a multiple of
336 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
337 the difference that is bounded by a small value. */
339 double dyear = (double) year_requested + mon_years - tm.tm_year;
340 double dday = 366 * dyear + mday;
341 double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
343 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
344 correct results, ie., it erroneously gives a positive value
345 of 715827882. Setting a variable first then doing math on it
346 seems to work. (ghazi@caip.rutgers.edu) */
348 const time_t time_t_max = TIME_T_MAX;
349 const time_t time_t_min = TIME_T_MIN;
351 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
360 static long int localtime_offset;
362 /* Convert *TP to a time_t value. */
364 mktime (struct tm *tp)
367 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
368 time zone names contained in the external variable `tzname' shall
369 be set as if the tzset() function had been called. */
373 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
377 weak_alias (mktime, timelocal)
381 libc_hidden_def (mktime)
382 libc_hidden_weak (timelocal)
388 not_equal_tm (struct tm const *a, struct tm const *b)
390 return ((a->tm_sec ^ b->tm_sec)
391 | (a->tm_min ^ b->tm_min)
392 | (a->tm_hour ^ b->tm_hour)
393 | (a->tm_mday ^ b->tm_mday)
394 | (a->tm_mon ^ b->tm_mon)
395 | (a->tm_year ^ b->tm_year)
396 | (a->tm_mday ^ b->tm_mday)
397 | (a->tm_yday ^ b->tm_yday)
398 | (a->tm_isdst ^ b->tm_isdst));
402 print_tm (struct tm const *tp)
405 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
406 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
407 tp->tm_hour, tp->tm_min, tp->tm_sec,
408 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
414 check_result (time_t tk, struct tm tmk, time_t tl, struct tm const *lt)
416 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
420 printf (")\nyields (");
422 printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
430 main (int argc, char **argv)
433 struct tm tm, tmk, tml;
438 if ((argc == 3 || argc == 4)
439 && (sscanf (argv[1], "%d-%d-%d%c",
440 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
442 && (sscanf (argv[2], "%d:%d:%d%c",
443 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
446 tm.tm_year -= TM_YEAR_BASE;
448 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
451 lt = localtime (&tl);
457 printf ("mktime returns %ld == ", (long) tl);
460 status = check_result (tl, tmk, tl, lt);
462 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
464 time_t from = atol (argv[1]);
465 time_t by = atol (argv[2]);
466 time_t to = atol (argv[3]);
469 for (tl = from; tl <= to; tl += by)
471 lt = localtime (&tl);
476 status |= check_result (tk, tmk, tl, &tml);
480 printf ("localtime (%ld) yields 0\n", (long) tl);
485 for (tl = from; tl <= to; tl += by)
487 /* Null benchmark. */
488 lt = localtime (&tl);
493 status |= check_result (tk, tmk, tl, &tml);
497 printf ("localtime (%ld) yields 0\n", (long) tl);
504 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
505 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
506 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
507 argv[0], argv[0], argv[0]);
516 compile-command: "gcc -DDEBUG -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"