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
21 /* Define this to have a standalone program to test this implementation of
30 # define HAVE_LIMITS_H 1
31 # define STDC_HEADERS 1
32 # define STATIC /* empty */
34 # define STATIC static
37 /* Assume that leap seconds are possible, unless told otherwise.
38 If the host has a `zic' command with a `-L leapsecondfilename' option,
39 then it supports leap seconds; otherwise it probably doesn't. */
40 #ifndef LEAP_SECONDS_POSSIBLE
41 # define LEAP_SECONDS_POSSIBLE 1
44 #include <sys/types.h> /* Some systems define `time_t' here. */
57 /* Make it work even if the system's libc has its own mktime routine. */
58 # define mktime my_mktime
62 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
63 # define __P(args) args
73 /* The extra casts work around common compiler bugs. */
74 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
75 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
76 It is necessary at least when t == time_t. */
77 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
78 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
79 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
82 # define INT_MIN TYPE_MINIMUM (int)
85 # define INT_MAX TYPE_MAXIMUM (int)
89 # define TIME_T_MIN TYPE_MINIMUM (time_t)
92 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
95 #define TM_YEAR_BASE 1900
96 #define EPOCH_YEAR 1970
99 /* Nonzero if YEAR is a leap year (every 4 years,
100 except every 100th isn't, and every 400th is). */
101 # define __isleap(year) \
102 ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
105 /* How many days come before each month (0-12). */
106 STATIC const unsigned short int __mon_yday[2][13] =
109 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
111 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
116 # define my_mktime_localtime_r __localtime_r
118 /* If we're a mktime substitute in a GNU program, then prefer
119 localtime to localtime_r, since many localtime_r implementations
122 my_mktime_localtime_r (const time_t *t, struct tm *tp)
124 struct tm *l = localtime (t);
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. */
140 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
147 /* Compute intervening leap days correctly even if year is negative.
148 Take care to avoid int overflow. time_t overflow is OK, since
149 only the low order bits of the correct time_t answer are needed.
150 Don't convert to time_t until after all divisions are done, since
151 time_t might be unsigned. */
152 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
153 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
154 int a100 = a4 / 25 - (a4 % 25 < 0);
155 int b100 = b4 / 25 - (b4 % 25 < 0);
156 int a400 = a100 >> 2;
157 int b400 = b100 >> 2;
158 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
159 time_t years = year - (time_t) tp->tm_year;
160 time_t days = (365 * years + intervening_leap_days
161 + (yday - tp->tm_yday));
162 return (60 * (60 * (24 * days + (hour - tp->tm_hour))
163 + (min - tp->tm_min))
164 + (sec - tp->tm_sec));
168 /* Use CONVERT to convert *T to a broken down time in *TP.
169 If *T is out of range for conversion, adjust it so that
170 it is the nearest in-range value and then convert that. */
172 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
173 time_t *t, struct tm *tp)
177 if (! (r = (*convert) (t, tp)) && *t)
183 /* BAD is a known unconvertible time_t, and OK is a known good one.
184 Use binary search to narrow the range between BAD and OK until
186 while (bad != ok + (bad < 0 ? -1 : 1))
188 time_t mid = *t = (bad < 0
189 ? bad + ((ok - bad) >> 1)
190 : ok + ((bad - ok) >> 1));
191 if ((r = (*convert) (t, tp)))
202 /* The last conversion attempt failed;
203 revert to the most recent successful attempt. */
214 /* Convert *TP to a time_t value, inverting
215 the monotonic and mostly-unit-linear conversion function CONVERT.
216 Use *OFFSET to keep track of a guess at the offset of the result,
217 compared to what the result would be for UTC without leap seconds.
218 If *OFFSET's guess is correct, only one CONVERT call is needed. */
220 __mktime_internal (struct tm *tp,
221 struct tm *(*convert) (const time_t *, struct tm *),
224 time_t t, dt, t0, t1, t2;
227 /* The maximum number of probes (calls to CONVERT) should be enough
228 to handle any combinations of time zone rule changes, solar time,
229 leap seconds, and oscillations around a spring-forward gap.
230 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
231 int remaining_probes = 6;
233 /* Time requested. Copy it in case CONVERT modifies *TP; this can
234 occur if TP is localtime's returned value and CONVERT is localtime. */
235 int sec = tp->tm_sec;
236 int min = tp->tm_min;
237 int hour = tp->tm_hour;
238 int mday = tp->tm_mday;
239 int mon = tp->tm_mon;
240 int year_requested = tp->tm_year;
241 int isdst = tp->tm_isdst;
243 /* 1 if the previous probe was DST. */
246 /* Ensure that mon is in range, and set year accordingly. */
247 int mon_remainder = mon % 12;
248 int negative_mon_remainder = mon_remainder < 0;
249 int mon_years = mon / 12 - negative_mon_remainder;
250 int year = year_requested + mon_years;
252 /* The other values need not be in range:
253 the remaining code handles minor overflows correctly,
254 assuming int and time_t arithmetic wraps around.
255 Major overflows are caught at the end. */
257 /* Calculate day of year from year, month, and day of month.
258 The result need not be in range. */
259 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
260 [mon_remainder + 12 * negative_mon_remainder])
263 int sec_requested = sec;
265 /* Only years after 1970 are defined.
266 If year is 69, it might still be representable due to
267 timezone differences. */
271 #if LEAP_SECONDS_POSSIBLE
272 /* Handle out-of-range seconds specially,
273 since ydhms_tm_diff assumes every minute has 60 seconds. */
280 /* Invert CONVERT by probing. First assume the same offset as last time.
281 Then repeatedly use the error to improve the guess. */
283 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
284 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
285 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
287 for (t = t1 = t2 = t0 + *offset, dst2 = 0;
288 (dt = ydhms_tm_diff (year, yday, hour, min, sec,
289 ranged_convert (convert, &t, &tm)));
290 t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
291 if (t == t1 && t != t2
294 ? dst2 <= (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. (If no tm_isdst
302 was requested and only one of the two values has a nonzero
303 tm_isdst, prefer that value.) In practice, this is more
304 useful than returning -1. */
306 else if (--remaining_probes == 0)
309 /* If we have a match, check whether tm.tm_isdst has the requested
311 if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
313 /* tm.tm_isdst has the wrong value. Look for a neighboring
314 time with the right value, and use its UTC offset.
315 Heuristic: probe the previous three calendar quarters (approximately),
316 looking for the desired isdst. This isn't perfect,
317 but it's good enough in practice. */
318 int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
321 /* If we're too close to the time_t limit, look in future quarters. */
322 if (t < TIME_T_MIN + 3 * quarter)
325 for (i = 1; i <= 3; i++)
327 time_t ot = t - i * quarter;
329 ranged_convert (convert, &ot, &otm);
330 if (otm.tm_isdst == isdst)
332 /* We found the desired tm_isdst.
333 Extrapolate back to the desired time. */
334 t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
335 ranged_convert (convert, &t, &tm);
343 #if LEAP_SECONDS_POSSIBLE
344 if (sec_requested != tm.tm_sec)
346 /* Adjust time to reflect the tm_sec requested, not the normalized value.
347 Also, repair any damage from a false match due to a leap second. */
348 t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
349 if (! (*convert) (&t, &tm))
354 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
356 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
357 so check for major overflows. A gross check suffices,
358 since if t has overflowed, it is off by a multiple of
359 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of
360 the difference that is bounded by a small value. */
362 double dyear = (double) year_requested + mon_years - tm.tm_year;
363 double dday = 366 * dyear + mday;
364 double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
366 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
367 correct results, ie., it erroneously gives a positive value
368 of 715827882. Setting a variable first then doing math on it
369 seems to work. (ghazi@caip.rutgers.edu) */
371 const time_t time_t_max = TIME_T_MAX;
372 const time_t time_t_min = TIME_T_MIN;
374 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
380 /* If year was 69, need to check whether the time was representable
382 if (t < 0 || t > 2 * 24 * 60 * 60)
391 static time_t localtime_offset;
393 /* Convert *TP to a time_t value. */
399 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
400 time zone names contained in the external variable `tzname' shall
401 be set as if the tzset() function had been called. */
405 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
409 weak_alias (mktime, timelocal)
413 libc_hidden_def (mktime)
414 libc_hidden_weak (timelocal)
424 return ((a->tm_sec ^ b->tm_sec)
425 | (a->tm_min ^ b->tm_min)
426 | (a->tm_hour ^ b->tm_hour)
427 | (a->tm_mday ^ b->tm_mday)
428 | (a->tm_mon ^ b->tm_mon)
429 | (a->tm_year ^ b->tm_year)
430 | (a->tm_mday ^ b->tm_mday)
431 | (a->tm_yday ^ b->tm_yday)
432 | (a->tm_isdst ^ b->tm_isdst));
440 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
441 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
442 tp->tm_hour, tp->tm_min, tp->tm_sec,
443 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
449 check_result (tk, tmk, tl, lt)
455 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
459 printf (")\nyields (");
461 printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
474 struct tm tm, tmk, tml;
479 if ((argc == 3 || argc == 4)
480 && (sscanf (argv[1], "%d-%d-%d%c",
481 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
483 && (sscanf (argv[2], "%d:%d:%d%c",
484 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
487 tm.tm_year -= TM_YEAR_BASE;
489 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
492 lt = localtime (&tl);
498 printf ("mktime returns %ld == ", (long) tl);
501 status = check_result (tl, tmk, tl, lt);
503 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
505 time_t from = atol (argv[1]);
506 time_t by = atol (argv[2]);
507 time_t to = atol (argv[3]);
510 for (tl = from; tl <= to; tl += by)
512 lt = localtime (&tl);
517 status |= check_result (tk, tmk, tl, tml);
521 printf ("localtime (%ld) yields 0\n", (long) tl);
526 for (tl = from; tl <= to; tl += by)
528 /* Null benchmark. */
529 lt = localtime (&tl);
534 status |= check_result (tk, tmk, tl, tml);
538 printf ("localtime (%ld) yields 0\n", (long) tl);
545 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
546 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
547 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
548 argv[0], argv[0], argv[0]);
557 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"