time/mktime.c

   1 /* Copyright (C) 1993, 94, 95, 96, 97, 98 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Paul Eggert (eggert@twinsun.com).
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 /* Define this to have a standalone program to test this implementation of
  21    mktime.  */
  22 /* #define DEBUG 1 */
  23
  24 #ifdef HAVE_CONFIG_H
  25 # include <config.h>
  26 #endif
  27
  28 /* Some systems require that one of these symbols be defined in
  29    order to declare localtime_r properly.  */
  30 #ifndef __EXTENSIONS__
  31 # define __EXTENSIONS__ 1
  32 #endif
  33 #ifndef _POSIX_THREAD_SAFE_FUNCTIONS
  34 # define _POSIX_THREAD_SAFE_FUNCTIONS 1
  35 #endif
  36
  37 #ifdef _LIBC
  38 # define HAVE_LIMITS_H 1
  39 # define HAVE_LOCALTIME_R 1
  40 # define STDC_HEADERS 1
  41 #endif
  42
  43 /* Assume that leap seconds are possible, unless told otherwise.
  44    If the host has a `zic' command with a `-L leapsecondfilename' option,
  45    then it supports leap seconds; otherwise it probably doesn't.  */
  46 #ifndef LEAP_SECONDS_POSSIBLE
  47 # define LEAP_SECONDS_POSSIBLE 1
  48 #endif
  49
  50 /* Some systems require <unistd.h> to be included before <time.h>
  51    for localtime_r to be declared properly.  */
  52 #if HAVE_UNISTD_H
  53 # include <unistd.h>
  54 #endif
  55
  56 #include <sys/types.h>          /* Some systems define `time_t' here.  */
  57 #include <time.h>
  58
  59 #if HAVE_LIMITS_H
  60 # include <limits.h>
  61 #endif
  62
  63 #if DEBUG
  64 # include <stdio.h>
  65 # if STDC_HEADERS
  66 #  include <stdlib.h>
  67 # endif
  68 /* Make it work even if the system's libc has its own mktime routine.  */
  69 # define mktime my_mktime
  70 #endif /* DEBUG */
  71
  72 #ifndef __P
  73 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
  74 #  define __P(args) args
  75 # else
  76 #  define __P(args) ()
  77 # endif  /* GCC.  */
  78 #endif  /* Not __P.  */
  79
  80 #ifndef CHAR_BIT
  81 # define CHAR_BIT 8
  82 #endif
  83
  84 /* The extra casts work around common compiler bugs.  */
  85 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  86 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
  87    It is necessary at least when t == time_t.  */
  88 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  89                               ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
  90 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  91
  92 #ifndef INT_MIN
  93 # define INT_MIN TYPE_MINIMUM (int)
  94 #endif
  95 #ifndef INT_MAX
  96 # define INT_MAX TYPE_MAXIMUM (int)
  97 #endif
  98
  99 #ifndef TIME_T_MIN
 100 # define TIME_T_MIN TYPE_MINIMUM (time_t)
 101 #endif
 102 #ifndef TIME_T_MAX
 103 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
 104 #endif
 105
 106 #define TM_YEAR_BASE 1900
 107 #define EPOCH_YEAR 1970
 108
 109 #ifndef __isleap
 110 /* Nonzero if YEAR is a leap year (every 4 years,
 111    except every 100th isn't, and every 400th is).  */
 112 # define __isleap(year) \
 113   ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
 114 #endif
 115
 116 /* How many days come before each month (0-12).  */
 117 const unsigned short int __mon_yday[2][13] =
 118   {
 119     /* Normal years.  */
 120     { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
 121     /* Leap years.  */
 122     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
 123   };
 124
 125 static struct tm *ranged_convert __P ((struct tm *(*) __P ((const time_t *,
 126                                                             struct tm *)),
 127                                        time_t *, struct tm *));
 128 static time_t ydhms_tm_diff __P ((int, int, int, int, int, const struct tm *));
 129 time_t __mktime_internal __P ((struct tm *,
 130                                struct tm *(*) (const time_t *, struct tm *),
 131                                time_t *));
 132
 133
 134 #ifdef _LIBC
 135 # define localtime_r __localtime_r
 136 #else
 137 # if HAVE_LOCALTIME_R == defined localtime_r
 138 /* Provide our own substitute for a missing or possibly broken localtime_r.  */
 139 static struct tm *my_mktime_localtime_r __P ((const time_t *, struct tm *));
 140 static struct tm *
 141 my_mktime_localtime_r (t, tp)
 142      const time_t *t;
 143      struct tm *tp;
 144 {
 145 #  ifdef localtime_r
 146   /* Digital Unix 4.0A and 4.0D have a macro localtime_r with the
 147      standard meaning, along with an unwanted, nonstandard function
 148      localtime_r.  The placeholder function my_mktime_localtime_r
 149      invokes the macro; use that instead of the system's bogus
 150      localtime_r.  */
 151   return localtime_r (t, tp);
 152 #   undef localtime_r
 153 #  else /* ! defined (localtime_r) */
 154   /* Approximate localtime_r as best we can in its absence.  */
 155   struct tm *l = localtime (t);
 156   if (! l)
 157     return 0;
 158   *tp = *l;
 159   return tp;
 160 #  endif /* ! defined localtime_r */
 161 }
 162 #  define localtime_r my_mktime_localtime_r
 163 # endif /* HAVE_LOCALTIME_R == defined localtime_r */
 164 #endif /* ! _LIBC */
 165
 166
 167 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
 168    measured in seconds, ignoring leap seconds.
 169    YEAR uses the same numbering as TM->tm_year.
 170    All values are in range, except possibly YEAR.
 171    If TP is null, return a nonzero value.
 172    If overflow occurs, yield the low order bits of the correct answer.  */
 173 static time_t
 174 ydhms_tm_diff (year, yday, hour, min, sec, tp)
 175      int year, yday, hour, min, sec;
 176      const struct tm *tp;
 177 {
 178   if (!tp)
 179     return 1;
 180   else
 181     {
 182       /* Compute intervening leap days correctly even if year is negative.
 183          Take care to avoid int overflow.  time_t overflow is OK, since
 184          only the low order bits of the correct time_t answer are needed.
 185          Don't convert to time_t until after all divisions are done, since
 186          time_t might be unsigned.  */
 187       int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
 188       int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
 189       int a100 = a4 / 25 - (a4 % 25 < 0);
 190       int b100 = b4 / 25 - (b4 % 25 < 0);
 191       int a400 = a100 >> 2;
 192       int b400 = b100 >> 2;
 193       int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
 194       time_t years = year - (time_t) tp->tm_year;
 195       time_t days = (365 * years + intervening_leap_days
 196                      + (yday - tp->tm_yday));
 197       return (60 * (60 * (24 * days + (hour - tp->tm_hour))
 198                     + (min - tp->tm_min))
 199               + (sec - tp->tm_sec));
 200     }
 201 }
 202
 203
 204 static time_t localtime_offset;
 205
 206 /* Convert *TP to a time_t value.  */
 207 time_t
 208 mktime (tp)
 209      struct tm *tp;
 210 {
 211 #ifdef _LIBC
 212   /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
 213      time zone names contained in the external variable `tzname' shall
 214      be set as if the tzset() function had been called.  */
 215   __tzset ();
 216 #endif
 217
 218   return __mktime_internal (tp, localtime_r, &localtime_offset);
 219 }
 220
 221 /* Use CONVERT to convert *T to a broken down time in *TP.
 222    If *T is out of range for conversion, adjust it so that
 223    it is the nearest in-range value and then convert that.  */
 224 static struct tm *
 225 ranged_convert (convert, t, tp)
 226      struct tm *(*convert) __P ((const time_t *, struct tm *));
 227      time_t *t;
 228      struct tm *tp;
 229 {
 230   struct tm *r;
 231
 232   if (! (r = (*convert) (t, tp)) && *t)
 233     {
 234       time_t bad = *t;
 235       time_t ok = 0;
 236       struct tm tm;
 237
 238       /* BAD is a known unconvertible time_t, and OK is a known good one.
 239          Use binary search to narrow the range between BAD and OK until
 240          they differ by 1.  */
 241       while (bad != ok + (bad < 0 ? -1 : 1))
 242         {
 243           time_t mid = *t = (bad < 0
 244                              ? bad + ((ok - bad) >> 1)
 245                              : ok + ((bad - ok) >> 1));
 246           if ((r = (*convert) (t, tp)))
 247             {
 248               tm = *r;
 249               ok = mid;
 250             }
 251           else
 252             bad = mid;
 253         }
 254
 255       if (!r && ok)
 256         {
 257           /* The last conversion attempt failed;
 258              revert to the most recent successful attempt.  */
 259           *t = ok;
 260           *tp = tm;
 261           r = tp;
 262         }
 263     }
 264
 265   return r;
 266 }
 267
 268
 269 /* Convert *TP to a time_t value, inverting
 270    the monotonic and mostly-unit-linear conversion function CONVERT.
 271    Use *OFFSET to keep track of a guess at the offset of the result,
 272    compared to what the result would be for UTC without leap seconds.
 273    If *OFFSET's guess is correct, only one CONVERT call is needed.  */
 274 time_t
 275 __mktime_internal (tp, convert, offset)
 276      struct tm *tp;
 277      struct tm *(*convert) __P ((const time_t *, struct tm *));
 278      time_t *offset;
 279 {
 280   time_t t, dt, t0, t1, t2;
 281   struct tm tm;
 282
 283   /* The maximum number of probes (calls to CONVERT) should be enough
 284      to handle any combinations of time zone rule changes, solar time,
 285      leap seconds, and oscillations around a spring-forward gap.
 286      POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
 287   int remaining_probes = 6;
 288
 289   /* Time requested.  Copy it in case CONVERT modifies *TP; this can
 290      occur if TP is localtime's returned value and CONVERT is localtime.  */
 291   int sec = tp->tm_sec;
 292   int min = tp->tm_min;
 293   int hour = tp->tm_hour;
 294   int mday = tp->tm_mday;
 295   int mon = tp->tm_mon;
 296   int year_requested = tp->tm_year;
 297   int isdst = tp->tm_isdst;
 298
 299   /* Ensure that mon is in range, and set year accordingly.  */
 300   int mon_remainder = mon % 12;
 301   int negative_mon_remainder = mon_remainder < 0;
 302   int mon_years = mon / 12 - negative_mon_remainder;
 303   int year = year_requested + mon_years;
 304
 305   /* The other values need not be in range:
 306      the remaining code handles minor overflows correctly,
 307      assuming int and time_t arithmetic wraps around.
 308      Major overflows are caught at the end.  */
 309
 310   /* Calculate day of year from year, month, and day of month.
 311      The result need not be in range.  */
 312   int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
 313                [mon_remainder + 12 * negative_mon_remainder])
 314               + mday - 1);
 315
 316   int sec_requested = sec;
 317 #if LEAP_SECONDS_POSSIBLE
 318   /* Handle out-of-range seconds specially,
 319      since ydhms_tm_diff assumes every minute has 60 seconds.  */
 320   if (sec < 0)
 321     sec = 0;
 322   if (59 < sec)
 323     sec = 59;
 324 #endif
 325
 326   /* Invert CONVERT by probing.  First assume the same offset as last time.
 327      Then repeatedly use the error to improve the guess.  */
 328
 329   tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
 330   tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
 331   t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
 332
 333   for (t = t1 = t2 = t0 + *offset;
 334        (dt = ydhms_tm_diff (year, yday, hour, min, sec,
 335                             ranged_convert (convert, &t, &tm)));
 336        t1 = t2, t2 = t, t += dt)
 337     if (t == t1 && t != t2
 338         && (isdst < 0 || tm.tm_isdst < 0
 339             || (isdst != 0) != (tm.tm_isdst != 0)))
 340       /* We can't possibly find a match, as we are oscillating
 341          between two values.  The requested time probably falls
 342          within a spring-forward gap of size DT.  Follow the common
 343          practice in this case, which is to return a time that is DT
 344          away from the requested time, preferring a time whose
 345          tm_isdst differs from the requested value.  In practice,
 346          this is more useful than returning -1.  */
 347       break;
 348     else if (--remaining_probes == 0)
 349       return -1;
 350
 351   /* If we have a match, check whether tm.tm_isdst has the requested
 352      value, if any.  */
 353   if (dt == 0 && 0 <= isdst && 0 <= tm.tm_isdst)
 354     {
 355       int dst_diff = (isdst != 0) - (tm.tm_isdst != 0);
 356       if (dst_diff)
 357         {
 358           /* Move two hours in the direction indicated by the disagreement,
 359              probe some more, and switch to a new time if found.
 360              The largest known fallback due to daylight savings is two hours:
 361              once, in Newfoundland, 1988-10-30 02:00 -> 00:00.  */
 362           time_t ot = t - 2 * 60 * 60 * dst_diff;
 363           while (--remaining_probes != 0)
 364             {
 365               struct tm otm;
 366               if (! (dt = ydhms_tm_diff (year, yday, hour, min, sec,
 367                                          ranged_convert (convert, &ot, &otm))))
 368                 {
 369                   t = ot;
 370                   tm = otm;
 371                   break;
 372                 }
 373               if ((ot += dt) == t)
 374                 break;  /* Avoid a redundant probe.  */
 375             }
 376         }
 377     }
 378
 379   *offset = t - t0;
 380
 381 #if LEAP_SECONDS_POSSIBLE
 382   if (sec_requested != tm.tm_sec)
 383     {
 384       /* Adjust time to reflect the tm_sec requested, not the normalized value.
 385          Also, repair any damage from a false match due to a leap second.  */
 386       t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
 387       if (! (*convert) (&t, &tm))
 388         return -1;
 389     }
 390 #endif
 391
 392   if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
 393     {
 394       /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
 395          so check for major overflows.  A gross check suffices,
 396          since if t has overflowed, it is off by a multiple of
 397          TIME_T_MAX - TIME_T_MIN + 1.  So ignore any component of
 398          the difference that is bounded by a small value.  */
 399
 400       double dyear = (double) year_requested + mon_years - tm.tm_year;
 401       double dday = 366 * dyear + mday;
 402       double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
 403
 404       /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
 405          correct results, ie., it erroneously gives a positive value
 406          of 715827882.  Setting a variable first then doing math on it
 407          seems to work.  (ghazi@caip.rutgers.edu) */
 408
 409       const time_t time_t_max = TIME_T_MAX;
 410       const time_t time_t_min = TIME_T_MIN;
 411
 412       if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
 413         return -1;
 414     }
 415
 416   *tp = tm;
 417   return t;
 418 }
 419
 420 #ifdef weak_alias
 421 weak_alias (mktime, timelocal)
 422 #endif
 423 \f
 424 #if DEBUG
 425
 426 static int
 427 not_equal_tm (a, b)
 428      struct tm *a;
 429      struct tm *b;
 430 {
 431   return ((a->tm_sec ^ b->tm_sec)
 432           | (a->tm_min ^ b->tm_min)
 433           | (a->tm_hour ^ b->tm_hour)
 434           | (a->tm_mday ^ b->tm_mday)
 435           | (a->tm_mon ^ b->tm_mon)
 436           | (a->tm_year ^ b->tm_year)
 437           | (a->tm_mday ^ b->tm_mday)
 438           | (a->tm_yday ^ b->tm_yday)
 439           | (a->tm_isdst ^ b->tm_isdst));
 440 }
 441
 442 static void
 443 print_tm (tp)
 444      struct tm *tp;
 445 {
 446   if (tp)
 447     printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
 448             tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
 449             tp->tm_hour, tp->tm_min, tp->tm_sec,
 450             tp->tm_yday, tp->tm_wday, tp->tm_isdst);
 451   else
 452     printf ("0");
 453 }
 454
 455 static int
 456 check_result (tk, tmk, tl, lt)
 457      time_t tk;
 458      struct tm tmk;
 459      time_t tl;
 460      struct tm *lt;
 461 {
 462   if (tk != tl || !lt || not_equal_tm (&tmk, lt))
 463     {
 464       printf ("mktime (");
 465       print_tm (&tmk);
 466       printf (")\nyields (");
 467       print_tm (lt);
 468       printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
 469       return 1;
 470     }
 471
 472   return 0;
 473 }
 474
 475 int
 476 main (argc, argv)
 477      int argc;
 478      char **argv;
 479 {
 480   int status = 0;
 481   struct tm tm, tmk, tml;
 482   struct tm *lt;
 483   time_t tk, tl;
 484   char trailer;
 485
 486   if ((argc == 3 || argc == 4)
 487       && (sscanf (argv[1], "%d-%d-%d%c",
 488                   &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
 489           == 3)
 490       && (sscanf (argv[2], "%d:%d:%d%c",
 491                   &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
 492           == 3))
 493     {
 494       tm.tm_year -= TM_YEAR_BASE;
 495       tm.tm_mon--;
 496       tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
 497       tmk = tm;
 498       tl = mktime (&tmk);
 499       lt = localtime (&tl);
 500       if (lt)
 501         {
 502           tml = *lt;
 503           lt = &tml;
 504         }
 505       printf ("mktime returns %ld == ", (long) tl);
 506       print_tm (&tmk);
 507       printf ("\n");
 508       status = check_result (tl, tmk, tl, lt);
 509     }
 510   else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
 511     {
 512       time_t from = atol (argv[1]);
 513       time_t by = atol (argv[2]);
 514       time_t to = atol (argv[3]);
 515
 516       if (argc == 4)
 517         for (tl = from; tl <= to; tl += by)
 518           {
 519             lt = localtime (&tl);
 520             if (lt)
 521               {
 522                 tmk = tml = *lt;
 523                 tk = mktime (&tmk);
 524                 status |= check_result (tk, tmk, tl, tml);
 525               }
 526             else
 527               {
 528                 printf ("localtime (%ld) yields 0\n", (long) tl);
 529                 status = 1;
 530               }
 531           }
 532       else
 533         for (tl = from; tl <= to; tl += by)
 534           {
 535             /* Null benchmark.  */
 536             lt = localtime (&tl);
 537             if (lt)
 538               {
 539                 tmk = tml = *lt;
 540                 tk = tl;
 541                 status |= check_result (tk, tmk, tl, tml);
 542               }
 543             else
 544               {
 545                 printf ("localtime (%ld) yields 0\n", (long) tl);
 546                 status = 1;
 547               }
 548           }
 549     }
 550   else
 551     printf ("Usage:\
 552 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
 553 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
 554 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
 555             argv[0], argv[0], argv[0]);
 556
 557   return status;
 558 }
 559
 560 #endif /* DEBUG */
 561 \f
 562 /*
 563 Local Variables:
 564 compile-command: "gcc -DDEBUG -D__EXTENSIONS__ -DHAVE_LIMITS_H -DHAVE_LOCALTIME_R -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
 565 End:
 566 */