src/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    Contributed by Paul Eggert (eggert@twinsun.com).
   4
   5    NOTE: The canonical source of this file is maintained with the GNU C Library.
   6    Bugs can be reported to bug-glibc@gnu.org.
   7
   8    This program is free software; you can redistribute it and/or modify it
   9    under the terms of the GNU General Public License as published by the
  10    Free Software Foundation; either version 2, or (at your option) any
  11    later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  21    USA.  */
  22
  23 /* Define this to have a standalone program to test this implementation of
  24    mktime.  */
  25 /* #define DEBUG 1 */
  26
  27 #ifdef HAVE_CONFIG_H
  28 # include <config.h>
  29 #endif
  30
  31 #ifdef _LIBC
  32 # define HAVE_LIMITS_H 1
  33 # define STDC_HEADERS 1
  34 #endif
  35
  36 /* Assume that leap seconds are possible, unless told otherwise.
  37    If the host has a `zic' command with a `-L leapsecondfilename' option,
  38    then it supports leap seconds; otherwise it probably doesn't.  */
  39 #ifndef LEAP_SECONDS_POSSIBLE
  40 # define LEAP_SECONDS_POSSIBLE 1
  41 #endif
  42
  43 #include <sys/types.h>          /* Some systems define `time_t' here.  */
  44 #include <time.h>
  45
  46 #if HAVE_LIMITS_H
  47 # include <limits.h>
  48 #endif
  49
  50 #if DEBUG
  51 # include <stdio.h>
  52 # if STDC_HEADERS
  53 #  include <stdlib.h>
  54 # endif
  55 /* Make it work even if the system's libc has its own mktime routine.  */
  56 # define mktime my_mktime
  57 #endif /* DEBUG */
  58
  59 #ifndef __P
  60 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
  61 #  define __P(args) args
  62 # else
  63 #  define __P(args) ()
  64 # endif  /* GCC.  */
  65 #endif  /* Not __P.  */
  66
  67 #ifndef CHAR_BIT
  68 # define CHAR_BIT 8
  69 #endif
  70
  71 /* The extra casts work around common compiler bugs.  */
  72 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  73 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
  74    It is necessary at least when t == time_t.  */
  75 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  76                               ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
  77 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  78
  79 #ifndef INT_MIN
  80 # define INT_MIN TYPE_MINIMUM (int)
  81 #endif
  82 #ifndef INT_MAX
  83 # define INT_MAX TYPE_MAXIMUM (int)
  84 #endif
  85
  86 #ifndef TIME_T_MIN
  87 # define TIME_T_MIN TYPE_MINIMUM (time_t)
  88 #endif
  89 #ifndef TIME_T_MAX
  90 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
  91 #endif
  92
  93 #define TM_YEAR_BASE 1900
  94 #define EPOCH_YEAR 1970
  95
  96 #ifndef __isleap
  97 /* Nonzero if YEAR is a leap year (every 4 years,
  98    except every 100th isn't, and every 400th is).  */
  99 # define __isleap(year) \
 100   ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
 101 #endif
 102
 103 /* How many days come before each month (0-12).  */
 104 const unsigned short int __mon_yday[2][13] =
 105   {
 106     /* Normal years.  */
 107     { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
 108     /* Leap years.  */
 109     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
 110   };
 111
 112
 113 #ifdef _LIBC
 114 # define my_mktime_localtime_r __localtime_r
 115 #else
 116 /* If we're a mktime substitute in a GNU program, then prefer
 117    localtime to localtime_r, since many localtime_r implementations
 118    are buggy.  */
 119 static struct tm *
 120 my_mktime_localtime_r (const time_t *t, struct tm *tp)
 121 {
 122   struct tm *l = localtime (t);
 123   if (! l)
 124     return 0;
 125   *tp = *l;
 126   return tp;
 127 }
 128 #endif /* ! _LIBC */
 129
 130
 131 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
 132    measured in seconds, ignoring leap seconds.
 133    YEAR uses the same numbering as TM->tm_year.
 134    All values are in range, except possibly YEAR.
 135    If TP is null, return a nonzero value.
 136    If overflow occurs, yield the low order bits of the correct answer.  */
 137 static time_t
 138 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
 139                const struct tm *tp)
 140 {
 141   if (!tp)
 142     return 1;
 143   else
 144     {
 145       /* Compute intervening leap days correctly even if year is negative.
 146          Take care to avoid int overflow.  time_t overflow is OK, since
 147          only the low order bits of the correct time_t answer are needed.
 148          Don't convert to time_t until after all divisions are done, since
 149          time_t might be unsigned.  */
 150       int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
 151       int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
 152       int a100 = a4 / 25 - (a4 % 25 < 0);
 153       int b100 = b4 / 25 - (b4 % 25 < 0);
 154       int a400 = a100 >> 2;
 155       int b400 = b100 >> 2;
 156       int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
 157       time_t years = year - (time_t) tp->tm_year;
 158       time_t days = (365 * years + intervening_leap_days
 159                      + (yday - tp->tm_yday));
 160       return (60 * (60 * (24 * days + (hour - tp->tm_hour))
 161                     + (min - tp->tm_min))
 162               + (sec - tp->tm_sec));
 163     }
 164 }
 165
 166 /* Use CONVERT to convert *T to a broken down time in *TP.
 167    If *T is out of range for conversion, adjust it so that
 168    it is the nearest in-range value and then convert that.  */
 169 static struct tm *
 170 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
 171                 time_t *t, struct tm *tp)
 172 {
 173   struct tm *r;
 174
 175   if (! (r = (*convert) (t, tp)) && *t)
 176     {
 177       time_t bad = *t;
 178       time_t ok = 0;
 179       struct tm tm;
 180
 181       /* BAD is a known unconvertible time_t, and OK is a known good one.
 182          Use binary search to narrow the range between BAD and OK until
 183          they differ by 1.  */
 184       while (bad != ok + (bad < 0 ? -1 : 1))
 185         {
 186           time_t mid = *t = (bad < 0
 187                              ? bad + ((ok - bad) >> 1)
 188                              : ok + ((bad - ok) >> 1));
 189           if ((r = (*convert) (t, tp)))
 190             {
 191               tm = *r;
 192               ok = mid;
 193             }
 194           else
 195             bad = mid;
 196         }
 197
 198       if (!r && ok)
 199         {
 200           /* The last conversion attempt failed;
 201              revert to the most recent successful attempt.  */
 202           *t = ok;
 203           *tp = tm;
 204           r = tp;
 205         }
 206     }
 207
 208   return r;
 209 }
 210
 211
 212 /* Convert *TP to a time_t value, inverting
 213    the monotonic and mostly-unit-linear conversion function CONVERT.
 214    Use *OFFSET to keep track of a guess at the offset of the result,
 215    compared to what the result would be for UTC without leap seconds.
 216    If *OFFSET's guess is correct, only one CONVERT call is needed.  */
 217 time_t
 218 __mktime_internal (struct tm *tp,
 219                    struct tm *(*convert) (const time_t *, struct tm *),
 220                    time_t *offset)
 221 {
 222   time_t t, dt, t0, t1, t2;
 223   struct tm tm;
 224
 225   /* The maximum number of probes (calls to CONVERT) should be enough
 226      to handle any combinations of time zone rule changes, solar time,
 227      leap seconds, and oscillations around a spring-forward gap.
 228      POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
 229   int remaining_probes = 6;
 230
 231   /* Time requested.  Copy it in case CONVERT modifies *TP; this can
 232      occur if TP is localtime's returned value and CONVERT is localtime.  */
 233   int sec = tp->tm_sec;
 234   int min = tp->tm_min;
 235   int hour = tp->tm_hour;
 236   int mday = tp->tm_mday;
 237   int mon = tp->tm_mon;
 238   int year_requested = tp->tm_year;
 239   int isdst = tp->tm_isdst;
 240
 241   /* Ensure that mon is in range, and set year accordingly.  */
 242   int mon_remainder = mon % 12;
 243   int negative_mon_remainder = mon_remainder < 0;
 244   int mon_years = mon / 12 - negative_mon_remainder;
 245   int year = year_requested + mon_years;
 246
 247   /* The other values need not be in range:
 248      the remaining code handles minor overflows correctly,
 249      assuming int and time_t arithmetic wraps around.
 250      Major overflows are caught at the end.  */
 251
 252   /* Calculate day of year from year, month, and day of month.
 253      The result need not be in range.  */
 254   int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
 255                [mon_remainder + 12 * negative_mon_remainder])
 256               + mday - 1);
 257
 258   int sec_requested = sec;
 259 #if LEAP_SECONDS_POSSIBLE
 260   /* Handle out-of-range seconds specially,
 261      since ydhms_tm_diff assumes every minute has 60 seconds.  */
 262   if (sec < 0)
 263     sec = 0;
 264   if (59 < sec)
 265     sec = 59;
 266 #endif
 267
 268   /* Invert CONVERT by probing.  First assume the same offset as last time.
 269      Then repeatedly use the error to improve the guess.  */
 270
 271   tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
 272   tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
 273   t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
 274
 275   for (t = t1 = t2 = t0 + *offset;
 276        (dt = ydhms_tm_diff (year, yday, hour, min, sec,
 277                             ranged_convert (convert, &t, &tm)));
 278        t1 = t2, t2 = t, t += dt)
 279     if (t == t1 && t != t2
 280         && (isdst < 0 || tm.tm_isdst < 0
 281             || (isdst != 0) != (tm.tm_isdst != 0)))
 282       /* We can't possibly find a match, as we are oscillating
 283          between two values.  The requested time probably falls
 284          within a spring-forward gap of size DT.  Follow the common
 285          practice in this case, which is to return a time that is DT
 286          away from the requested time, preferring a time whose
 287          tm_isdst differs from the requested value.  In practice,
 288          this is more useful than returning -1.  */
 289       break;
 290     else if (--remaining_probes == 0)
 291       return -1;
 292
 293   /* If we have a match, check whether tm.tm_isdst has the requested
 294      value, if any.  */
 295   if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
 296     {
 297       /* tm.tm_isdst has the wrong value.  Look for a neighboring
 298          time with the right value, and use its UTC offset.
 299          Heuristic: probe the previous three calendar quarters (approximately),
 300          looking for the desired isdst.  This isn't perfect,
 301          but it's good enough in practice.  */
 302       int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
 303       int i;
 304
 305       /* If we're too close to the time_t limit, look in future quarters.  */
 306       if (t < TIME_T_MIN + 3 * quarter)
 307         quarter = -quarter;
 308
 309       for (i = 1; i <= 3; i++)
 310         {
 311           time_t ot = t - i * quarter;
 312           struct tm otm;
 313           ranged_convert (convert, &ot, &otm);
 314           if (otm.tm_isdst == isdst)
 315             {
 316               /* We found the desired tm_isdst.
 317                  Extrapolate back to the desired time.  */
 318               t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
 319               ranged_convert (convert, &t, &tm);
 320               break;
 321             }
 322         }
 323     }
 324
 325   *offset = t - t0;
 326
 327 #if LEAP_SECONDS_POSSIBLE
 328   if (sec_requested != tm.tm_sec)
 329     {
 330       /* Adjust time to reflect the tm_sec requested, not the normalized value.
 331          Also, repair any damage from a false match due to a leap second.  */
 332       t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
 333       if (! (*convert) (&t, &tm))
 334         return -1;
 335     }
 336 #endif
 337
 338   if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
 339     {
 340       /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
 341          so check for major overflows.  A gross check suffices,
 342          since if t has overflowed, it is off by a multiple of
 343          TIME_T_MAX - TIME_T_MIN + 1.  So ignore any component of
 344          the difference that is bounded by a small value.  */
 345
 346       double dyear = (double) year_requested + mon_years - tm.tm_year;
 347       double dday = 366 * dyear + mday;
 348       double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
 349
 350       /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
 351          correct results, ie., it erroneously gives a positive value
 352          of 715827882.  Setting a variable first then doing math on it
 353          seems to work.  (ghazi@caip.rutgers.edu) */
 354
 355       const time_t time_t_max = TIME_T_MAX;
 356       const time_t time_t_min = TIME_T_MIN;
 357
 358       if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
 359         return -1;
 360     }
 361
 362   *tp = tm;
 363   return t;
 364 }
 365
 366
 367 static time_t localtime_offset;
 368
 369 /* Convert *TP to a time_t value.  */
 370 time_t
 371 mktime (tp)
 372      struct tm *tp;
 373 {
 374 #ifdef _LIBC
 375   /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
 376      time zone names contained in the external variable `tzname' shall
 377      be set as if the tzset() function had been called.  */
 378   __tzset ();
 379 #endif
 380
 381   return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
 382 }
 383
 384 #ifdef weak_alias
 385 weak_alias (mktime, timelocal)
 386 #endif
 387 \f
 388 #if DEBUG
 389
 390 static int
 391 not_equal_tm (a, b)
 392      struct tm *a;
 393      struct tm *b;
 394 {
 395   return ((a->tm_sec ^ b->tm_sec)
 396           | (a->tm_min ^ b->tm_min)
 397           | (a->tm_hour ^ b->tm_hour)
 398           | (a->tm_mday ^ b->tm_mday)
 399           | (a->tm_mon ^ b->tm_mon)
 400           | (a->tm_year ^ b->tm_year)
 401           | (a->tm_mday ^ b->tm_mday)
 402           | (a->tm_yday ^ b->tm_yday)
 403           | (a->tm_isdst ^ b->tm_isdst));
 404 }
 405
 406 static void
 407 print_tm (tp)
 408      struct tm *tp;
 409 {
 410   if (tp)
 411     printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
 412             tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
 413             tp->tm_hour, tp->tm_min, tp->tm_sec,
 414             tp->tm_yday, tp->tm_wday, tp->tm_isdst);
 415   else
 416     printf ("0");
 417 }
 418
 419 static int
 420 check_result (tk, tmk, tl, lt)
 421      time_t tk;
 422      struct tm tmk;
 423      time_t tl;
 424      struct tm *lt;
 425 {
 426   if (tk != tl || !lt || not_equal_tm (&tmk, lt))
 427     {
 428       printf ("mktime (");
 429       print_tm (&tmk);
 430       printf (")\nyields (");
 431       print_tm (lt);
 432       printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
 433       return 1;
 434     }
 435
 436   return 0;
 437 }
 438
 439 int
 440 main (argc, argv)
 441      int argc;
 442      char **argv;
 443 {
 444   int status = 0;
 445   struct tm tm, tmk, tml;
 446   struct tm *lt;
 447   time_t tk, tl;
 448   char trailer;
 449
 450   if ((argc == 3 || argc == 4)
 451       && (sscanf (argv[1], "%d-%d-%d%c",
 452                   &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
 453           == 3)
 454       && (sscanf (argv[2], "%d:%d:%d%c",
 455                   &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
 456           == 3))
 457     {
 458       tm.tm_year -= TM_YEAR_BASE;
 459       tm.tm_mon--;
 460       tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
 461       tmk = tm;
 462       tl = mktime (&tmk);
 463       lt = localtime (&tl);
 464       if (lt)
 465         {
 466           tml = *lt;
 467           lt = &tml;
 468         }
 469       printf ("mktime returns %ld == ", (long) tl);
 470       print_tm (&tmk);
 471       printf ("\n");
 472       status = check_result (tl, tmk, tl, lt);
 473     }
 474   else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
 475     {
 476       time_t from = atol (argv[1]);
 477       time_t by = atol (argv[2]);
 478       time_t to = atol (argv[3]);
 479
 480       if (argc == 4)
 481         for (tl = from; tl <= to; tl += by)
 482           {
 483             lt = localtime (&tl);
 484             if (lt)
 485               {
 486                 tmk = tml = *lt;
 487                 tk = mktime (&tmk);
 488                 status |= check_result (tk, tmk, tl, tml);
 489               }
 490             else
 491               {
 492                 printf ("localtime (%ld) yields 0\n", (long) tl);
 493                 status = 1;
 494               }
 495           }
 496       else
 497         for (tl = from; tl <= to; tl += by)
 498           {
 499             /* Null benchmark.  */
 500             lt = localtime (&tl);
 501             if (lt)
 502               {
 503                 tmk = tml = *lt;
 504                 tk = tl;
 505                 status |= check_result (tk, tmk, tl, tml);
 506               }
 507             else
 508               {
 509                 printf ("localtime (%ld) yields 0\n", (long) tl);
 510                 status = 1;
 511               }
 512           }
 513     }
 514   else
 515     printf ("Usage:\
 516 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
 517 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
 518 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
 519             argv[0], argv[0], argv[0]);
 520
 521   return status;
 522 }
 523
 524 #endif /* DEBUG */
 525 \f
 526 /*
 527 Local Variables:
 528 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
 529 End:
 530 */