1/* Convert a `struct tm' to a time_t value. 2 Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, 2003, 3 2004, 2005, 2006, 2007 Free Software Foundation, Inc. 4 Contributed by Paul Eggert (eggert@twinsun.com). 5 6 NOTE: The canonical source of this file is maintained with the GNU C Library. 7 Bugs can be reported to bug-glibc@gnu.org. 8 9 This program is free software; you can redistribute it and/or modify it 10 under the terms of the GNU General Public License as published by the 11 Free Software Foundation; either version 2, or (at your option) any 12 later version. 13 14 This program is distributed in the hope that it will be useful, 15 but WITHOUT ANY WARRANTY; without even the implied warranty of 16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 17 GNU General Public License for more details. 18 19 You should have received a copy of the GNU General Public License 20 along with this program; if not, write to the Free Software 21 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, 22 USA. */ 23 24/* Define this to have a standalone program to test this implementation of 25 mktime. */ 26/* #define DEBUG 1 */ 27 28#ifdef HAVE_CONFIG_H 29# include <config.h> 30#endif 31 32#ifdef _LIBC 33# define HAVE_LIMITS_H 1 34# define STDC_HEADERS 1 35#endif 36 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 42#endif 43 44#include <sys/types.h> /* Some systems define `time_t' here. */ 45#include <time.h> 46 47#if HAVE_LIMITS_H 48# include <limits.h> 49#endif 50 51#if DEBUG 52# include <stdio.h> 53# if STDC_HEADERS 54# include <stdlib.h> 55# endif 56/* Make it work even if the system's libc has its own mktime routine. */ 57# define mktime my_mktime 58#endif /* DEBUG */ 59 60#ifndef __P 61# if defined __GNUC__ || (defined __STDC__ && __STDC__) 62# define __P(args) args 63# else 64# define __P(args) () 65# endif /* GCC. */ 66#endif /* Not __P. */ 67 68#ifndef CHAR_BIT 69# define CHAR_BIT 8 70#endif 71 72/* The extra casts work around common compiler bugs. */ 73#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1)) 74/* The outer cast is needed to work around a bug in Cray C 5.0.3.0. 75 It is necessary at least when t == time_t. */ 76#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \ 77 ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0)) 78#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t))) 79 80#ifndef INT_MIN 81# define INT_MIN TYPE_MINIMUM (int) 82#endif 83#ifndef INT_MAX 84# define INT_MAX TYPE_MAXIMUM (int) 85#endif 86 87#ifndef TIME_T_MIN 88# define TIME_T_MIN TYPE_MINIMUM (time_t) 89#endif 90#ifndef TIME_T_MAX 91# define TIME_T_MAX TYPE_MAXIMUM (time_t) 92#endif 93 94#define TM_YEAR_BASE 1900 95#define EPOCH_YEAR 1970 96 97#ifndef __isleap 98/* Nonzero if YEAR is a leap year (every 4 years, 99 except every 100th isn't, and every 400th is). */ 100# define __isleap(year) \ 101 ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0)) 102#endif 103 104/* How many days come before each month (0-12). */ 105const unsigned short int __mon_yday[2][13] = 106 { 107 /* Normal years. */ 108 { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 }, 109 /* Leap years. */ 110 { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 } 111 }; 112 113 114#ifdef _LIBC 115# define my_mktime_localtime_r __localtime_r 116#else 117/* If we're a mktime substitute in a GNU program, then prefer 118 localtime to localtime_r, since many localtime_r implementations 119 are buggy. */ 120static struct tm * 121my_mktime_localtime_r (t, tp) 122 const time_t *t; 123 struct tm *tp; 124{ 125 struct tm *l = localtime (t); 126 if (! l) 127 return 0; 128 *tp = *l; 129 return tp; 130} 131#endif /* ! _LIBC */ 132 133 134/* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP), 135 measured in seconds, ignoring leap seconds. 136 YEAR uses the same numbering as TM->tm_year. 137 All values are in range, except possibly YEAR. 138 If TP is null, return a nonzero value. 139 If overflow occurs, yield the low order bits of the correct answer. */ 140static time_t 141ydhms_tm_diff (year, yday, hour, min, sec, tp) 142 int year, yday, hour, min, sec; 143 const struct tm *tp; 144{ 145 if (!tp) 146 return 1; 147 else 148 { 149 /* Compute intervening leap days correctly even if year is negative. 150 Take care to avoid int overflow. time_t overflow is OK, since 151 only the low order bits of the correct time_t answer are needed. 152 Don't convert to time_t until after all divisions are done, since 153 time_t might be unsigned. */ 154 int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3); 155 int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3); 156 int a100 = a4 / 25 - (a4 % 25 < 0); 157 int b100 = b4 / 25 - (b4 % 25 < 0); 158 int a400 = a100 >> 2; 159 int b400 = b100 >> 2; 160 int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400); 161 time_t years = year - (time_t) tp->tm_year; 162 time_t days = (365 * years + intervening_leap_days 163 + (yday - tp->tm_yday)); 164 return (60 * (60 * (24 * days + (hour - tp->tm_hour)) 165 + (min - tp->tm_min)) 166 + (sec - tp->tm_sec)); 167 } 168} 169 170/* Use CONVERT to convert *T to a broken down time in *TP. 171 If *T is out of range for conversion, adjust it so that 172 it is the nearest in-range value and then convert that. */ 173static struct tm * 174ranged_convert (convert, t, tp) 175#ifdef PROTOTYPES 176 struct tm *(*convert) (const time_t *, struct tm *); 177#else 178 struct tm *(*convert)(); 179#endif 180 time_t *t; 181 struct tm *tp; 182{ 183 struct tm *r; 184 185 if (! (r = (*convert) (t, tp)) && *t) 186 { 187 time_t bad = *t; 188 time_t ok = 0; 189 struct tm tm; 190 191 /* BAD is a known unconvertible time_t, and OK is a known good one. 192 Use binary search to narrow the range between BAD and OK until 193 they differ by 1. */ 194 while (bad != ok + (bad < 0 ? -1 : 1)) 195 { 196 time_t mid = *t = (bad < 0 197 ? bad + ((ok - bad) >> 1) 198 : ok + ((bad - ok) >> 1)); 199 if ((r = (*convert) (t, tp))) 200 { 201 tm = *r; 202 ok = mid; 203 } 204 else 205 bad = mid; 206 } 207 208 if (!r && ok) 209 { 210 /* The last conversion attempt failed; 211 revert to the most recent successful attempt. */ 212 *t = ok; 213 *tp = tm; 214 r = tp; 215 } 216 } 217 218 return r; 219} 220 221 222/* Convert *TP to a time_t value, inverting 223 the monotonic and mostly-unit-linear conversion function CONVERT. 224 Use *OFFSET to keep track of a guess at the offset of the result, 225 compared to what the result would be for UTC without leap seconds. 226 If *OFFSET's guess is correct, only one CONVERT call is needed. */ 227time_t 228__mktime_internal (tp, convert, offset) 229 struct tm *tp; 230#ifdef PROTOTYPES 231 struct tm *(*convert) (const time_t *, struct tm *); 232#else 233 struct tm *(*convert)(); 234#endif 235 time_t *offset; 236{ 237 time_t t, dt, t0, t1, t2; 238 struct tm tm; 239 240 /* The maximum number of probes (calls to CONVERT) should be enough 241 to handle any combinations of time zone rule changes, solar time, 242 leap seconds, and oscillations around a spring-forward gap. 243 POSIX.1 prohibits leap seconds, but some hosts have them anyway. */ 244 int remaining_probes = 6; 245 246 /* Time requested. Copy it in case CONVERT modifies *TP; this can 247 occur if TP is localtime's returned value and CONVERT is localtime. */ 248 int sec = tp->tm_sec; 249 int min = tp->tm_min; 250 int hour = tp->tm_hour; 251 int mday = tp->tm_mday; 252 int mon = tp->tm_mon; 253 int year_requested = tp->tm_year; 254 int isdst = tp->tm_isdst; 255 256 /* 1 if the previous probe was DST. */ 257 int dst2; 258 259 /* Ensure that mon is in range, and set year accordingly. */ 260 int mon_remainder = mon % 12; 261 int negative_mon_remainder = mon_remainder < 0; 262 int mon_years = mon / 12 - negative_mon_remainder; 263 int year = year_requested + mon_years; 264 265 /* The other values need not be in range: 266 the remaining code handles minor overflows correctly, 267 assuming int and time_t arithmetic wraps around. 268 Major overflows are caught at the end. */ 269 270 /* Calculate day of year from year, month, and day of month. 271 The result need not be in range. */ 272 int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)] 273 [mon_remainder + 12 * negative_mon_remainder]) 274 + mday - 1); 275 276 int sec_requested = sec; 277 278 /* Only years after 1970 are defined. 279 If year is 69, it might still be representable due to 280 timezone differences. */ 281 if (year < 69) 282 return -1; 283 284#if LEAP_SECONDS_POSSIBLE 285 /* Handle out-of-range seconds specially, 286 since ydhms_tm_diff assumes every minute has 60 seconds. */ 287 if (sec < 0) 288 sec = 0; 289 if (59 < sec) 290 sec = 59; 291#endif 292 293 /* Invert CONVERT by probing. First assume the same offset as last time. 294 Then repeatedly use the error to improve the guess. */ 295 296 tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE; 297 tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0; 298 t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm); 299 300 for (t = t1 = t2 = t0 + *offset, dst2 = 0; 301 (dt = ydhms_tm_diff (year, yday, hour, min, sec, 302 ranged_convert (convert, &t, &tm))); 303 t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0) 304 if (t == t1 && t != t2 305 && (tm.tm_isdst < 0 306 || (isdst < 0 307 ? dst2 <= (tm.tm_isdst != 0) 308 : (isdst != 0) != (tm.tm_isdst != 0)))) 309 /* We can't possibly find a match, as we are oscillating 310 between two values. The requested time probably falls 311 within a spring-forward gap of size DT. Follow the common 312 practice in this case, which is to return a time that is DT 313 away from the requested time, preferring a time whose 314 tm_isdst differs from the requested value. (If no tm_isdst 315 was requested and only one of the two values has a nonzero 316 tm_isdst, prefer that value.) In practice, this is more 317 useful than returning -1. */ 318 break; 319 else if (--remaining_probes == 0) 320 return -1; 321 322 /* If we have a match, check whether tm.tm_isdst has the requested 323 value, if any. */ 324 if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst) 325 { 326 /* tm.tm_isdst has the wrong value. Look for a neighboring 327 time with the right value, and use its UTC offset. 328 Heuristic: probe the previous three calendar quarters (approximately), 329 looking for the desired isdst. This isn't perfect, 330 but it's good enough in practice. */ 331 int quarter = 7889238; /* seconds per average 1/4 Gregorian year */ 332 int i; 333 334 /* If we're too close to the time_t limit, look in future quarters. */ 335 if (t < TIME_T_MIN + 3 * quarter) 336 quarter = -quarter; 337 338 for (i = 1; i <= 3; i++) 339 { 340 time_t ot = t - i * quarter; 341 struct tm otm; 342 ranged_convert (convert, &ot, &otm); 343 if (otm.tm_isdst == isdst) 344 { 345 /* We found the desired tm_isdst. 346 Extrapolate back to the desired time. */ 347 t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm); 348 ranged_convert (convert, &t, &tm); 349 break; 350 } 351 } 352 } 353 354 *offset = t - t0; 355 356#if LEAP_SECONDS_POSSIBLE 357 if (sec_requested != tm.tm_sec) 358 { 359 /* Adjust time to reflect the tm_sec requested, not the normalized value. 360 Also, repair any damage from a false match due to a leap second. */ 361 t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60); 362 if (! (*convert) (&t, &tm)) 363 return -1; 364 } 365#endif 366 367 if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3) 368 { 369 /* time_t isn't large enough to rule out overflows in ydhms_tm_diff, 370 so check for major overflows. A gross check suffices, 371 since if t has overflowed, it is off by a multiple of 372 TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of 373 the difference that is bounded by a small value. */ 374 375 double dyear = (double) year_requested + mon_years - tm.tm_year; 376 double dday = 366 * dyear + mday; 377 double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested; 378 379 /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce 380 correct results, ie., it erroneously gives a positive value 381 of 715827882. Setting a variable first then doing math on it 382 seems to work. (ghazi@caip.rutgers.edu) */ 383 384 const time_t time_t_max = TIME_T_MAX; 385 const time_t time_t_min = TIME_T_MIN; 386 387 if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec)) 388 return -1; 389 } 390 391 if (year == 69) 392 { 393 /* If year was 69, need to check whether the time was representable 394 or not. */ 395 if (t < 0 || t > 2 * 24 * 60 * 60) 396 return -1; 397 } 398 399 *tp = tm; 400 return t; 401} 402 403 404static time_t localtime_offset; 405 406/* Convert *TP to a time_t value. */ 407time_t 408mktime (tp) 409 struct tm *tp; 410{ 411#ifdef _LIBC 412 /* POSIX.1 8.1.1 requires that whenever mktime() is called, the 413 time zone names contained in the external variable `tzname' shall 414 be set as if the tzset() function had been called. */ 415 __tzset (); 416#endif 417 418 return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset); 419} 420 421#ifdef weak_alias 422weak_alias (mktime, timelocal) 423#endif 424 425#if DEBUG 426 427static int 428not_equal_tm (a, b) 429 struct tm *a; 430 struct tm *b; 431{ 432 return ((a->tm_sec ^ b->tm_sec) 433 | (a->tm_min ^ b->tm_min) 434 | (a->tm_hour ^ b->tm_hour) 435 | (a->tm_mday ^ b->tm_mday) 436 | (a->tm_mon ^ b->tm_mon) 437 | (a->tm_year ^ b->tm_year) 438 | (a->tm_mday ^ b->tm_mday) 439 | (a->tm_yday ^ b->tm_yday) 440 | (a->tm_isdst ^ b->tm_isdst)); 441} 442 443static void 444print_tm (tp) 445 struct tm *tp; 446{ 447 if (tp) 448 printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d", 449 tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday, 450 tp->tm_hour, tp->tm_min, tp->tm_sec, 451 tp->tm_yday, tp->tm_wday, tp->tm_isdst); 452 else 453 printf ("0"); 454} 455 456static int 457check_result (tk, tmk, tl, lt) 458 time_t tk; 459 struct tm tmk; 460 time_t tl; 461 struct tm *lt; 462{ 463 if (tk != tl || !lt || not_equal_tm (&tmk, lt)) 464 { 465 printf ("mktime ("); 466 print_tm (&tmk); 467 printf (")\nyields ("); 468 print_tm (lt); 469 printf (") == %ld, should be %ld\n", (long) tl, (long) tk); 470 return 1; 471 } 472 473 return 0; 474} 475 476int 477main (argc, argv) 478 int argc; 479 char **argv; 480{ 481 int status = 0; 482 struct tm tm, tmk, tml; 483 struct tm *lt; 484 time_t tk, tl; 485 char trailer; 486 487 if ((argc == 3 || argc == 4) 488 && (sscanf (argv[1], "%d-%d-%d%c", 489 &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer) 490 == 3) 491 && (sscanf (argv[2], "%d:%d:%d%c", 492 &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer) 493 == 3)) 494 { 495 tm.tm_year -= TM_YEAR_BASE; 496 tm.tm_mon--; 497 tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]); 498 tmk = tm; 499 tl = mktime (&tmk); 500 lt = localtime (&tl); 501 if (lt) 502 { 503 tml = *lt; 504 lt = &tml; 505 } 506 printf ("mktime returns %ld == ", (long) tl); 507 print_tm (&tmk); 508 printf ("\n"); 509 status = check_result (tl, tmk, tl, lt); 510 } 511 else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0)) 512 { 513 time_t from = atol (argv[1]); 514 time_t by = atol (argv[2]); 515 time_t to = atol (argv[3]); 516 517 if (argc == 4) 518 for (tl = from; tl <= to; tl += by) 519 { 520 lt = localtime (&tl); 521 if (lt) 522 { 523 tmk = tml = *lt; 524 tk = mktime (&tmk); 525 status |= check_result (tk, tmk, tl, tml); 526 } 527 else 528 { 529 printf ("localtime (%ld) yields 0\n", (long) tl); 530 status = 1; 531 } 532 } 533 else 534 for (tl = from; tl <= to; tl += by) 535 { 536 /* Null benchmark. */ 537 lt = localtime (&tl); 538 if (lt) 539 { 540 tmk = tml = *lt; 541 tk = tl; 542 status |= check_result (tk, tmk, tl, tml); 543 } 544 else 545 { 546 printf ("localtime (%ld) yields 0\n", (long) tl); 547 status = 1; 548 } 549 } 550 } 551 else 552 printf ("Usage:\ 553\t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\ 554\t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\ 555\t%s FROM BY TO - # Do not test those values (for benchmark).\n", 556 argv[0], argv[0], argv[0]); 557 558 return status; 559} 560 561#endif /* DEBUG */ 562 563/* 564Local Variables: 565compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime" 566End: 567*/ 568 569/* arch-tag: 9456752f-7ddd-47cb-8286-fa807b1355ae 570 (do not change this comment) */ 571