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). */
109 const unsigned short int __mon_yday[2][13] =
112 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
114 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
119 # define my_mktime_localtime_r __localtime_r
121 /* If we're a mktime substitute in a GNU program, then prefer
122 localtime to localtime_r, since many localtime_r implementations
125 my_mktime_localtime_r (const time_t *t, struct tm *tp)
127 struct tm *l = localtime (t);
136 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
137 measured in seconds, ignoring leap seconds.
138 YEAR uses the same numbering as TM->tm_year.
139 All values are in range, except possibly YEAR.
140 If TP is null, return a nonzero value.
141 If overflow occurs, yield the low order bits of the correct answer. */
143 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
150 /* Compute intervening leap days correctly even if year is negative.
151 Take care to avoid int overflow. time_t overflow is OK, since
152 only the low order bits of the correct time_t answer are needed.
153 Don't convert to time_t until after all divisions are done, since
154 time_t might be unsigned. */
155 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
156 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
157 int a100 = a4 / 25 - (a4 % 25 < 0);
158 int b100 = b4 / 25 - (b4 % 25 < 0);
159 int a400 = a100 >> 2;
160 int b400 = b100 >> 2;
161 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
162 time_t years = year - (time_t) tp->tm_year;
163 time_t days = (365 * years + intervening_leap_days
164 + (yday - tp->tm_yday));
165 return (60 * (60 * (24 * days + (hour - tp->tm_hour))
166 + (min - tp->tm_min))
167 + (sec - tp->tm_sec));
171 /* Use CONVERT to convert *T to a broken down time in *TP.
172 If *T is out of range for conversion, adjust it so that
173 it is the nearest in-range value and then convert that. */
175 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
176 time_t *t, struct tm *tp)
180 if (! (r = (*convert) (t, tp)) && *t)
186 /* BAD is a known unconvertible time_t, and OK is a known good one.
187 Use binary search to narrow the range between BAD and OK until
189 while (bad != ok + (bad < 0 ? -1 : 1))
191 time_t mid = *t = (bad < 0
192 ? bad + ((ok - bad) >> 1)
193 : ok + ((bad - ok) >> 1));
194 if ((r = (*convert) (t, tp)))
205 /* The last conversion attempt failed;
206 revert to the most recent successful attempt. */
217 /* Convert *TP to a time_t value, inverting
218 the monotonic and mostly-unit-linear conversion function CONVERT.
219 Use *OFFSET to keep track of a guess at the offset of the result,
220 compared to what the result would be for UTC without leap seconds.
221 If *OFFSET's guess is correct, only one CONVERT call is needed. */
226 __mktime_internal (struct tm *tp,
227 struct tm *(*convert) (const time_t *, struct tm *),
230 time_t t, dt, t0, t1, t2;
233 /* The maximum number of probes (calls to CONVERT) should be enough
234 to handle any combinations of time zone rule changes, solar time,
235 leap seconds, and oscillations around a spring-forward gap.
236 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */
237 int remaining_probes = 6;
239 /* Time requested. Copy it in case CONVERT modifies *TP; this can
240 occur if TP is localtime's returned value and CONVERT is localtime. */
241 int sec = tp->tm_sec;
242 int min = tp->tm_min;
243 int hour = tp->tm_hour;
244 int mday = tp->tm_mday;
245 int mon = tp->tm_mon;
246 int year_requested = tp->tm_year;
247 int isdst = tp->tm_isdst;
249 /* 1 if the previous probe was DST. */
252 /* Ensure that mon is in range, and set year accordingly. */
253 int mon_remainder = mon % 12;
254 int negative_mon_remainder = mon_remainder < 0;
255 int mon_years = mon / 12 - negative_mon_remainder;
256 int year = year_requested + mon_years;
258 /* The other values need not be in range:
259 the remaining code handles minor overflows correctly,
260 assuming int and time_t arithmetic wraps around.
261 Major overflows are caught at the end. */
263 /* Calculate day of year from year, month, and day of month.
264 The result need not be in range. */
265 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
266 [mon_remainder + 12 * negative_mon_remainder])
269 int sec_requested = sec;
271 /* Only years after 1970 are defined.
272 If year is 69, it might still be representable due to
273 timezone differences. */
277 #if LEAP_SECONDS_POSSIBLE
278 /* Handle out-of-range seconds specially,
279 since ydhms_tm_diff assumes every minute has 60 seconds. */
286 /* Invert CONVERT by probing. First assume the same offset as last time.
287 Then repeatedly use the error to improve the guess. */
289 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
290 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
291 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
293 for (t = t1 = t2 = t0 + *offset, dst2 = 0;
294 (dt = ydhms_tm_diff (year, yday, hour, min, sec,
295 ranged_convert (convert, &t, &tm)));
296 t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
297 if (t == t1 && t != t2
300 ? dst2 <= (tm.tm_isdst != 0)
301 : (isdst != 0) != (tm.tm_isdst != 0))))
302 /* We can't possibly find a match, as we are oscillating
303 between two values. The requested time probably falls
304 within a spring-forward gap of size DT. Follow the common
305 practice in this case, which is to return a time that is DT
306 away from the requested time, preferring a time whose
307 tm_isdst differs from the requested value. (If no tm_isdst
308 was requested and only one of the two values has a nonzero
309 tm_isdst, prefer that value.) In practice, this is more
310 useful than returning -1. */
312 else if (--remaining_probes == 0)
315 /* If we have a match, check whether tm.tm_isdst has the requested
317 if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
319 /* tm.tm_isdst has the wrong value. Look for a neighboring
320 time with the right value, and use its UTC offset.
321 Heuristic: probe the previous three calendar quarters (approximately),
322 looking for the desired isdst. This isn't perfect,
323 but it's good enough in practice. */
324 int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
327 /* If we're too close to the time_t limit, look in future quarters. */
328 if (t < TIME_T_MIN + 3 * quarter)
331 for (i = 1; i <= 3; i++)
333 time_t ot = t - i * quarter;
335 ranged_convert (convert, &ot, &otm);
336 if (otm.tm_isdst == isdst)
338 /* We found the desired tm_isdst.
339 Extrapolate back to the desired time. */
340 t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
341 ranged_convert (convert, &t, &tm);
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))
386 /* If year was 69, need to check whether the time was representable
388 if (t < 0 || t > 2 * 24 * 60 * 60)
397 static time_t localtime_offset;
399 /* Convert *TP to a time_t value. */
405 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
406 time zone names contained in the external variable `tzname' shall
407 be set as if the tzset() function had been called. */
411 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
415 weak_alias (mktime, timelocal)
419 libc_hidden_def (mktime)
420 libc_hidden_weak (timelocal)
430 return ((a->tm_sec ^ b->tm_sec)
431 | (a->tm_min ^ b->tm_min)
432 | (a->tm_hour ^ b->tm_hour)
433 | (a->tm_mday ^ b->tm_mday)
434 | (a->tm_mon ^ b->tm_mon)
435 | (a->tm_year ^ b->tm_year)
436 | (a->tm_mday ^ b->tm_mday)
437 | (a->tm_yday ^ b->tm_yday)
438 | (a->tm_isdst ^ b->tm_isdst));
446 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
447 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
448 tp->tm_hour, tp->tm_min, tp->tm_sec,
449 tp->tm_yday, tp->tm_wday, tp->tm_isdst);
455 check_result (tk, tmk, tl, lt)
461 if (tk != tl || !lt || not_equal_tm (&tmk, lt))
465 printf (")\nyields (");
467 printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
480 struct tm tm, tmk, tml;
485 if ((argc == 3 || argc == 4)
486 && (sscanf (argv[1], "%d-%d-%d%c",
487 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
489 && (sscanf (argv[2], "%d:%d:%d%c",
490 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
493 tm.tm_year -= TM_YEAR_BASE;
495 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
498 lt = localtime (&tl);
504 printf ("mktime returns %ld == ", (long) tl);
507 status = check_result (tl, tmk, tl, lt);
509 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
511 time_t from = atol (argv[1]);
512 time_t by = atol (argv[2]);
513 time_t to = atol (argv[3]);
516 for (tl = from; tl <= to; tl += by)
518 lt = localtime (&tl);
523 status |= check_result (tk, tmk, tl, tml);
527 printf ("localtime (%ld) yields 0\n", (long) tl);
532 for (tl = from; tl <= to; tl += by)
534 /* Null benchmark. */
535 lt = localtime (&tl);
540 status |= check_result (tk, tmk, tl, tml);
544 printf ("localtime (%ld) yields 0\n", (long) tl);
551 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
552 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
553 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
554 argv[0], argv[0], argv[0]);
563 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"