time/mktime.c

   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).
   5
   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.
  10
  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.
  15
  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
  19    02111-1307 USA.  */
  20
  21 /* Define this to have a standalone program to test this implementation of
  22    mktime.  */
  23 /* #define DEBUG 1 */
  24
  25 #ifdef HAVE_CONFIG_H
  26 # include <config.h>
  27 #endif
  28
  29 #ifdef _LIBC
  30 # define HAVE_LIMITS_H 1
  31 # define STDC_HEADERS 1
  32 #endif
  33
  34 /* Assume that leap seconds are possible, unless told otherwise.
  35    If the host has a `zic' command with a `-L leapsecondfilename' option,
  36    then it supports leap seconds; otherwise it probably doesn't.  */
  37 #ifndef LEAP_SECONDS_POSSIBLE
  38 # define LEAP_SECONDS_POSSIBLE 1
  39 #endif
  40
  41 #include <sys/types.h>          /* Some systems define `time_t' here.  */
  42 #include <time.h>
  43
  44 #if HAVE_LIMITS_H
  45 # include <limits.h>
  46 #endif
  47
  48 #if DEBUG
  49 # include <stdio.h>
  50 # if STDC_HEADERS
  51 #  include <stdlib.h>
  52 #  include <string.h>
  53 # endif
  54 /* Make it work even if the system's libc has its own mktime routine.  */
  55 # define mktime my_mktime
  56 #endif /* DEBUG */
  57
  58 #ifndef __P
  59 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
  60 #  define __P(args) args
  61 # else
  62 #  define __P(args) ()
  63 # endif  /* GCC.  */
  64 #endif  /* Not __P.  */
  65
  66 #ifndef CHAR_BIT
  67 # define CHAR_BIT 8
  68 #endif
  69
  70 /* The extra casts work around common compiler bugs.  */
  71 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  72 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
  73    It is necessary at least when t == time_t.  */
  74 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  75                               ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
  76 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  77
  78 #ifndef INT_MIN
  79 # define INT_MIN TYPE_MINIMUM (int)
  80 #endif
  81 #ifndef INT_MAX
  82 # define INT_MAX TYPE_MAXIMUM (int)
  83 #endif
  84
  85 #ifndef TIME_T_MIN
  86 # define TIME_T_MIN TYPE_MINIMUM (time_t)
  87 #endif
  88 #ifndef TIME_T_MAX
  89 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
  90 #endif
  91
  92 #define TM_YEAR_BASE 1900
  93 #define EPOCH_YEAR 1970
  94
  95 #ifndef __isleap
  96 /* Nonzero if YEAR is a leap year (every 4 years,
  97    except every 100th isn't, and every 400th is).  */
  98 # define __isleap(year) \
  99   ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
 100 #endif
 101
 102 /* How many days come before each month (0-12).  */
 103 #ifndef _LIBC
 104 static
 105 #endif
 106 const unsigned short int __mon_yday[2][13] =
 107   {
 108     /* Normal years.  */
 109     { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
 110     /* Leap years.  */
 111     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
 112   };
 113
 114
 115 #ifdef _LIBC
 116 # define my_mktime_localtime_r __localtime_r
 117 #else
 118 /* If we're a mktime substitute in a GNU program, then prefer
 119    localtime to localtime_r, since many localtime_r implementations
 120    are buggy.  */
 121 static struct tm *
 122 my_mktime_localtime_r (const time_t *t, struct tm *tp)
 123 {
 124   struct tm *l = localtime (t);
 125   if (! l)
 126     return 0;
 127   *tp = *l;
 128   return tp;
 129 }
 130 #endif /* ! _LIBC */
 131
 132
 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.  */
 139 static time_t
 140 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
 141                const struct tm *tp)
 142 {
 143   if (!tp)
 144     return 1;
 145   else
 146     {
 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));
 165     }
 166 }
 167
 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.  */
 171 static struct tm *
 172 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
 173                 time_t *t, struct tm *tp)
 174 {
 175   struct tm *r;
 176
 177   if (! (r = (*convert) (t, tp)) && *t)
 178     {
 179       time_t bad = *t;
 180       time_t ok = 0;
 181       struct tm tm;
 182
 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
 185          they differ by 1.  */
 186       while (bad != ok + (bad < 0 ? -1 : 1))
 187         {
 188           time_t mid = *t = (bad < 0
 189                              ? bad + ((ok - bad) >> 1)
 190                              : ok + ((bad - ok) >> 1));
 191           if ((r = (*convert) (t, tp)))
 192             {
 193               tm = *r;
 194               ok = mid;
 195             }
 196           else
 197             bad = mid;
 198         }
 199
 200       if (!r && ok)
 201         {
 202           /* The last conversion attempt failed;
 203              revert to the most recent successful attempt.  */
 204           *t = ok;
 205           *tp = tm;
 206           r = tp;
 207         }
 208     }
 209
 210   return r;
 211 }
 212
 213
 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.  */
 219 #ifndef _LIBC
 220 static
 221 #endif
 222 time_t
 223 __mktime_internal (struct tm *tp,
 224                    struct tm *(*convert) (const time_t *, struct tm *),
 225                    time_t *offset)
 226 {
 227   time_t t, dt, t0, t1, t2;
 228   struct tm tm;
 229
 230   /* The maximum number of probes (calls to CONVERT) should be enough
 231      to handle any combinations of time zone rule changes, solar time,
 232      leap seconds, and oscillations around a spring-forward gap.
 233      POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
 234   int remaining_probes = 6;
 235
 236   /* Time requested.  Copy it in case CONVERT modifies *TP; this can
 237      occur if TP is localtime's returned value and CONVERT is localtime.  */
 238   int sec = tp->tm_sec;
 239   int min = tp->tm_min;
 240   int hour = tp->tm_hour;
 241   int mday = tp->tm_mday;
 242   int mon = tp->tm_mon;
 243   int year_requested = tp->tm_year;
 244   int isdst = tp->tm_isdst;
 245
 246   /* 1 if the previous probe was DST.  */
 247   int dst2;
 248
 249   /* Ensure that mon is in range, and set year accordingly.  */
 250   int mon_remainder = mon % 12;
 251   int negative_mon_remainder = mon_remainder < 0;
 252   int mon_years = mon / 12 - negative_mon_remainder;
 253   int year = year_requested + mon_years;
 254
 255   /* The other values need not be in range:
 256      the remaining code handles minor overflows correctly,
 257      assuming int and time_t arithmetic wraps around.
 258      Major overflows are caught at the end.  */
 259
 260   /* Calculate day of year from year, month, and day of month.
 261      The result need not be in range.  */
 262   int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
 263                [mon_remainder + 12 * negative_mon_remainder])
 264               + mday - 1);
 265
 266   int sec_requested = sec;
 267
 268   /* Only years after 1970 are defined.
 269      If year is 69, it might still be representable due to
 270      timezone differences.  */
 271   if (year < 69)
 272     return -1;
 273
 274 #if LEAP_SECONDS_POSSIBLE
 275   /* Handle out-of-range seconds specially,
 276      since ydhms_tm_diff assumes every minute has 60 seconds.  */
 277   if (sec < 0)
 278     sec = 0;
 279   if (59 < sec)
 280     sec = 59;
 281 #endif
 282
 283   /* Invert CONVERT by probing.  First assume the same offset as last time.
 284      Then repeatedly use the error to improve the guess.  */
 285
 286   tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
 287   tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
 288   t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
 289
 290   for (t = t1 = t2 = t0 + *offset, dst2 = 0;
 291        (dt = ydhms_tm_diff (year, yday, hour, min, sec,
 292                             ranged_convert (convert, &t, &tm)));
 293        t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
 294     if (t == t1 && t != t2
 295         && (tm.tm_isdst < 0
 296             || (isdst < 0
 297                 ? dst2 <= (tm.tm_isdst != 0)
 298                 : (isdst != 0) != (tm.tm_isdst != 0))))
 299       /* We can't possibly find a match, as we are oscillating
 300          between two values.  The requested time probably falls
 301          within a spring-forward gap of size DT.  Follow the common
 302          practice in this case, which is to return a time that is DT
 303          away from the requested time, preferring a time whose
 304          tm_isdst differs from the requested value.  (If no tm_isdst
 305          was requested and only one of the two values has a nonzero
 306          tm_isdst, prefer that value.)  In practice, this is more
 307          useful than returning -1.  */
 308       break;
 309     else if (--remaining_probes == 0)
 310       return -1;
 311
 312   /* If we have a match, check whether tm.tm_isdst has the requested
 313      value, if any.  */
 314   if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
 315     {
 316       /* tm.tm_isdst has the wrong value.  Look for a neighboring
 317          time with the right value, and use its UTC offset.
 318          Heuristic: probe the previous three calendar quarters (approximately),
 319          looking for the desired isdst.  This isn't perfect,
 320          but it's good enough in practice.  */
 321       int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
 322       int i;
 323
 324       /* If we're too close to the time_t limit, look in future quarters.  */
 325       if (t < TIME_T_MIN + 3 * quarter)
 326         quarter = -quarter;
 327
 328       for (i = 1; i <= 3; i++)
 329         {
 330           time_t ot = t - i * quarter;
 331           struct tm otm;
 332           ranged_convert (convert, &ot, &otm);
 333           if (otm.tm_isdst == isdst)
 334             {
 335               /* We found the desired tm_isdst.
 336                  Extrapolate back to the desired time.  */
 337               t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
 338               ranged_convert (convert, &t, &tm);
 339               break;
 340             }
 341         }
 342     }
 343
 344   *offset = t - t0;
 345
 346 #if LEAP_SECONDS_POSSIBLE
 347   if (sec_requested != tm.tm_sec)
 348     {
 349       /* Adjust time to reflect the tm_sec requested, not the normalized value.
 350          Also, repair any damage from a false match due to a leap second.  */
 351       t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
 352       if (! (*convert) (&t, &tm))
 353         return -1;
 354     }
 355 #endif
 356
 357   if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
 358     {
 359       /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
 360          so check for major overflows.  A gross check suffices,
 361          since if t has overflowed, it is off by a multiple of
 362          TIME_T_MAX - TIME_T_MIN + 1.  So ignore any component of
 363          the difference that is bounded by a small value.  */
 364
 365       double dyear = (double) year_requested + mon_years - tm.tm_year;
 366       double dday = 366 * dyear + mday;
 367       double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
 368
 369       /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
 370          correct results, ie., it erroneously gives a positive value
 371          of 715827882.  Setting a variable first then doing math on it
 372          seems to work.  (ghazi@caip.rutgers.edu) */
 373
 374       const time_t time_t_max = TIME_T_MAX;
 375       const time_t time_t_min = TIME_T_MIN;
 376
 377       if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
 378         return -1;
 379     }
 380
 381   if (year == 69)
 382     {
 383       /* If year was 69, need to check whether the time was representable
 384          or not.  */
 385       if (t < 0 || t > 2 * 24 * 60 * 60)
 386         return -1;
 387     }
 388
 389   *tp = tm;
 390   return t;
 391 }
 392
 393
 394 static time_t localtime_offset;
 395
 396 /* Convert *TP to a time_t value.  */
 397 time_t
 398 mktime (tp)
 399      struct tm *tp;
 400 {
 401 #ifdef _LIBC
 402   /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
 403      time zone names contained in the external variable `tzname' shall
 404      be set as if the tzset() function had been called.  */
 405   __tzset ();
 406 #endif
 407
 408   return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
 409 }
 410
 411 #ifdef weak_alias
 412 weak_alias (mktime, timelocal)
 413 #endif
 414
 415 #ifdef _LIBC
 416 libc_hidden_def (mktime)
 417 libc_hidden_weak (timelocal)
 418 #endif
 419 \f
 420 #if DEBUG
 421
 422 static int
 423 not_equal_tm (a, b)
 424      struct tm *a;
 425      struct tm *b;
 426 {
 427   return ((a->tm_sec ^ b->tm_sec)
 428           | (a->tm_min ^ b->tm_min)
 429           | (a->tm_hour ^ b->tm_hour)
 430           | (a->tm_mday ^ b->tm_mday)
 431           | (a->tm_mon ^ b->tm_mon)
 432           | (a->tm_year ^ b->tm_year)
 433           | (a->tm_mday ^ b->tm_mday)
 434           | (a->tm_yday ^ b->tm_yday)
 435           | (a->tm_isdst ^ b->tm_isdst));
 436 }
 437
 438 static void
 439 print_tm (tp)
 440      struct tm *tp;
 441 {
 442   if (tp)
 443     printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
 444             tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
 445             tp->tm_hour, tp->tm_min, tp->tm_sec,
 446             tp->tm_yday, tp->tm_wday, tp->tm_isdst);
 447   else
 448     printf ("0");
 449 }
 450
 451 static int
 452 check_result (tk, tmk, tl, lt)
 453      time_t tk;
 454      struct tm tmk;
 455      time_t tl;
 456      struct tm *lt;
 457 {
 458   if (tk != tl || !lt || not_equal_tm (&tmk, lt))
 459     {
 460       printf ("mktime (");
 461       print_tm (&tmk);
 462       printf (")\nyields (");
 463       print_tm (lt);
 464       printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
 465       return 1;
 466     }
 467
 468   return 0;
 469 }
 470
 471 int
 472 main (argc, argv)
 473      int argc;
 474      char **argv;
 475 {
 476   int status = 0;
 477   struct tm tm, tmk, tml;
 478   struct tm *lt;
 479   time_t tk, tl;
 480   char trailer;
 481
 482   if ((argc == 3 || argc == 4)
 483       && (sscanf (argv[1], "%d-%d-%d%c",
 484                   &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
 485           == 3)
 486       && (sscanf (argv[2], "%d:%d:%d%c",
 487                   &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
 488           == 3))
 489     {
 490       tm.tm_year -= TM_YEAR_BASE;
 491       tm.tm_mon--;
 492       tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
 493       tmk = tm;
 494       tl = mktime (&tmk);
 495       lt = localtime (&tl);
 496       if (lt)
 497         {
 498           tml = *lt;
 499           lt = &tml;
 500         }
 501       printf ("mktime returns %ld == ", (long) tl);
 502       print_tm (&tmk);
 503       printf ("\n");
 504       status = check_result (tl, tmk, tl, lt);
 505     }
 506   else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
 507     {
 508       time_t from = atol (argv[1]);
 509       time_t by = atol (argv[2]);
 510       time_t to = atol (argv[3]);
 511
 512       if (argc == 4)
 513         for (tl = from; tl <= to; tl += by)
 514           {
 515             lt = localtime (&tl);
 516             if (lt)
 517               {
 518                 tmk = tml = *lt;
 519                 tk = mktime (&tmk);
 520                 status |= check_result (tk, tmk, tl, tml);
 521               }
 522             else
 523               {
 524                 printf ("localtime (%ld) yields 0\n", (long) tl);
 525                 status = 1;
 526               }
 527           }
 528       else
 529         for (tl = from; tl <= to; tl += by)
 530           {
 531             /* Null benchmark.  */
 532             lt = localtime (&tl);
 533             if (lt)
 534               {
 535                 tmk = tml = *lt;
 536                 tk = tl;
 537                 status |= check_result (tk, tmk, tl, tml);
 538               }
 539             else
 540               {
 541                 printf ("localtime (%ld) yields 0\n", (long) tl);
 542                 status = 1;
 543               }
 544           }
 545     }
 546   else
 547     printf ("Usage:\
 548 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
 549 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
 550 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
 551             argv[0], argv[0], argv[0]);
 552
 553   return status;
 554 }
 555
 556 #endif /* DEBUG */
 557 \f
 558 /*
 559 Local Variables:
 560 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
 561 End:
 562 */