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