lib/mktime.c

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