lib/mktime.c

   1 /* Copyright (C) 1993, 1994 Free Software Foundation, Inc.
   2    Contributed by Noel Cragg (noel@cs.oberlin.edu), with fixes by
   3    Michael E. Calwas (calwas@ttd.teradyne.com) and
   4    Wade Hampton (tasi029@tmn.com).
   5
   6
   7 NOTE: The canonical source of this file is maintained with the GNU C Library.
   8 Bugs can be reported to bug-glibc@prep.ai.mit.edu.
   9
  10 This program is free software; you can redistribute it and/or modify it
  11 under the terms of the GNU General Public License as published by the
  12 Free Software Foundation; either version 2, or (at your option) any
  13 later version.
  14
  15 This program is distributed in the hope that it will be useful,
  16 but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 GNU General Public License for more details.
  19
  20 You should have received a copy of the GNU General Public License
  21 along with this program; if not, write to the Free Software
  22 Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  23
  24 /* Define this to have a standalone program to test this implementation of
  25    mktime.  */
  26 /* #define DEBUG */
  27
  28 #ifdef HAVE_CONFIG_H
  29 #include <config.h>
  30 #endif
  31
  32 #include <sys/types.h>          /* Some systems define `time_t' here.  */
  33 #include <time.h>
  34
  35
  36 #ifndef __isleap
  37 /* Nonzero if YEAR is a leap year (every 4 years,
  38    except every 100th isn't, and every 400th is).  */
  39 #define __isleap(year)  \
  40   ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
  41 #endif
  42
  43 #ifndef __P
  44 #if defined (__GNUC__) || (defined (__STDC__) && __STDC__)
  45 #define __P(args) args
  46 #else
  47 #define __P(args) ()
  48 #endif  /* GCC.  */
  49 #endif  /* Not __P.  */
  50
  51 /* How many days are in each month.  */
  52 const unsigned short int __mon_lengths[2][12] =
  53   {
  54     /* Normal years.  */
  55     { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
  56     /* Leap years.  */
  57     { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
  58   };
  59
  60
  61 static int times_through_search; /* This library routine should never
  62                                     hang -- make sure we always return
  63                                     when we're searching for a value */
  64
  65
  66 #ifdef DEBUG
  67
  68 #include <stdio.h>
  69 #include <ctype.h>
  70
  71 int debugging_enabled = 0;
  72
  73 /* Print the values in a `struct tm'. */
  74 static void
  75 printtm (it)
  76      struct tm *it;
  77 {
  78   printf ("%02d/%02d/%04d %02d:%02d:%02d (%s) yday:%03d dst:%d gmtoffset:%ld",
  79           it->tm_mon + 1,
  80           it->tm_mday,
  81           it->tm_year + 1900,
  82           it->tm_hour,
  83           it->tm_min,
  84           it->tm_sec,
  85           it->tm_zone,
  86           it->tm_yday,
  87           it->tm_isdst,
  88           it->tm_gmtoff);
  89 }
  90 #endif
  91
  92
  93 static time_t
  94 dist_tm (t1, t2)
  95      struct tm *t1;
  96      struct tm *t2;
  97 {
  98   time_t distance = 0;
  99   unsigned long int v1, v2;
 100   int diff_flag = 0;
 101
 102   v1 = v2 = 0;
 103
 104 #define doit(x, secs)                                                         \
 105   v1 += t1->x * secs;                                                         \
 106   v2 += t2->x * secs;                                                         \
 107   if (!diff_flag)                                                             \
 108     {                                                                         \
 109       if (t1->x < t2->x)                                                      \
 110         diff_flag = -1;                                                       \
 111       else if (t1->x > t2->x)                                                 \
 112         diff_flag = 1;                                                        \
 113     }
 114
 115   doit (tm_year, 31536000);     /* Okay, not all years have 365 days. */
 116   doit (tm_mon, 2592000);       /* Okay, not all months have 30 days. */
 117   doit (tm_mday, 86400);
 118   doit (tm_hour, 3600);
 119   doit (tm_min, 60);
 120   doit (tm_sec, 1);
 121
 122 #undef doit
 123
 124   /* We should also make sure that the sign of DISTANCE is correct -- if
 125      DIFF_FLAG is positive, the distance should be positive and vice versa. */
 126
 127   distance = (v1 > v2) ? (v1 - v2) : (v2 - v1);
 128   if (diff_flag < 0)
 129     distance = -distance;
 130
 131   if (times_through_search > 20) /* Arbitrary # of calls, but makes sure we
 132                                     never hang if there's a problem with
 133                                     this algorithm.  */
 134     {
 135       distance = diff_flag;
 136     }
 137
 138   /* We need this DIFF_FLAG business because it is forseeable that the
 139      distance may be zero when, in actuality, the two structures are
 140      different.  This is usually the case when the dates are 366 days apart
 141      and one of the years is a leap year.  */
 142
 143   if (distance == 0 && diff_flag)
 144     distance = 86400 * diff_flag;
 145
 146   return distance;
 147 }
 148
 149
 150 /* MKTIME converts the values in a struct tm to a time_t.  The values
 151    in tm_wday and tm_yday are ignored; other values can be put outside
 152    of legal ranges since they will be normalized.  This routine takes
 153    care of that normalization. */
 154
 155 void
 156 do_normalization (tmptr)
 157      struct tm *tmptr;
 158 {
 159
 160 #define normalize(foo,x,y,bar); \
 161   while (tmptr->foo < x) \
 162     { \
 163       tmptr->bar--; \
 164       tmptr->foo = (y - (x - tmptr->foo) + 1); \
 165     } \
 166   while (tmptr->foo > y) \
 167     { \
 168       tmptr->foo = (x + (tmptr->foo - y) - 1); \
 169       tmptr->bar++; \
 170     }
 171
 172   normalize (tm_sec, 0, 59, tm_min);
 173   normalize (tm_min, 0, 59, tm_hour);
 174   normalize (tm_hour, 0, 23, tm_mday);
 175
 176   /* Do the month first, so day range can be found. */
 177   normalize (tm_mon, 0, 11, tm_year);
 178
 179   /* Since the day range modifies the month, we should be careful how
 180      we reference the array of month lengths -- it is possible that
 181      the month will go negative, hence the modulo...
 182
 183      Also, tm_year is the year - 1900, so we have to 1900 to have it
 184      work correctly. */
 185
 186   normalize (tm_mday, 1,
 187              __mon_lengths[__isleap (tmptr->tm_year + 1900)]
 188                           [((tmptr->tm_mon < 0)
 189                             ? (12 + (tmptr->tm_mon % 12))
 190                             : (tmptr->tm_mon % 12)) ],
 191              tm_mon);
 192
 193   /* Do the month again, because the day may have pushed it out of range. */
 194   normalize (tm_mon, 0, 11, tm_year);
 195
 196   /* Do the day again, because the month may have changed the range. */
 197   normalize (tm_mday, 1,
 198              __mon_lengths[__isleap (tmptr->tm_year + 1900)]
 199                           [((tmptr->tm_mon < 0)
 200                             ? (12 + (tmptr->tm_mon % 12))
 201                             : (tmptr->tm_mon % 12)) ],
 202              tm_mon);
 203
 204 #ifdef DEBUG
 205   if (debugging_enabled)
 206     {
 207       printf ("   After normalizing:\n     ");
 208       printtm (tmptr);
 209       putchar ('\n');
 210     }
 211 #endif
 212
 213 }
 214
 215
 216 /* Here's where the work gets done. */
 217
 218 #define BAD_STRUCT_TM ((time_t) -1)
 219
 220 time_t
 221 _mktime_internal (timeptr, producer)
 222      struct tm *timeptr;
 223      struct tm *(*producer) __P ((const time_t *));
 224 {
 225   struct tm our_tm;             /* our working space */
 226   struct tm *me = &our_tm;      /* a pointer to the above */
 227   time_t result;                /* the value we return */
 228
 229   *me = *timeptr;               /* copy the struct tm that was passed
 230                                    in by the caller */
 231
 232
 233   /***************************/
 234   /* Normalize the structure */
 235   /***************************/
 236
 237   /* This routine assumes that the value of TM_ISDST is -1, 0, or 1.
 238      If the user didn't pass it in that way, fix it. */
 239
 240   if (me->tm_isdst > 0)
 241     me->tm_isdst = 1;
 242   else if (me->tm_isdst < 0)
 243     me->tm_isdst = -1;
 244
 245   do_normalization (me);
 246
 247   /* Get out of here if it's not possible to represent this struct.
 248      If any of the values in the normalized struct tm are negative,
 249      our algorithms won't work.  Luckily, we only need to check the
 250      year at this point; normalization guarantees that all values will
 251      be in correct ranges EXCEPT the year. */
 252
 253   if (me->tm_year < 0)
 254     return BAD_STRUCT_TM;
 255
 256   /*************************************************/
 257   /* Find the appropriate time_t for the structure */
 258   /*************************************************/
 259
 260   /* Modified b-search -- make intelligent guesses as to where the
 261      time might lie along the timeline, assuming that our target time
 262      lies a linear distance (w/o considering time jumps of a
 263      particular region).
 264
 265      Assume that time does not fluctuate at all along the timeline --
 266      e.g., assume that a day will always take 86400 seconds, etc. --
 267      and come up with a hypothetical value for the time_t
 268      representation of the struct tm TARGET, in relation to the guess
 269      variable -- it should be pretty close!
 270
 271      After testing this, the maximum number of iterations that I had
 272      on any number that I tried was 3!  Not bad.
 273
 274      The reason this is not a subroutine is that we will modify some
 275      fields in the struct tm (yday and mday).  I've never felt good
 276      about side-effects when writing structured code... */
 277
 278   {
 279     struct tm *guess_tm;
 280     time_t guess = 0;
 281     time_t distance = 0;
 282     time_t last_distance = 0;
 283
 284     times_through_search = 0;
 285
 286     do
 287       {
 288         guess += distance;
 289
 290         times_through_search++;
 291
 292         guess_tm = (*producer) (&guess);
 293
 294 #ifdef DEBUG
 295         if (debugging_enabled)
 296           {
 297             printf ("   Guessing time_t == %d\n     ", (int) guess);
 298             printtm (guess_tm);
 299             putchar ('\n');
 300           }
 301 #endif
 302
 303         /* How far is our guess from the desired struct tm? */
 304         distance = dist_tm (me, guess_tm);
 305
 306         /* Handle periods of time where a period of time is skipped.
 307            For example, 2:15 3 April 1994 does not exist, because DST
 308            is in effect.  The distance function will alternately
 309            return values of 3600 and -3600, because it doesn't know
 310            that the requested time doesn't exist.  In these situations
 311            (even if the skip is not exactly an hour) the distances
 312            returned will be the same, but alternating in sign.  We
 313            want the later time, so check to see that the distance is
 314            oscillating and we've chosen the correct of the two
 315            possibilities.
 316
 317            Useful: 3 Apr 94 765356300, 30 Oct 94 783496000 */
 318
 319         if ((distance == -last_distance) && (distance < last_distance))
 320           {
 321             /* If the caller specified that the DST flag was off, it's
 322                not possible to represent this time. */
 323             if (me->tm_isdst == 0)
 324               {
 325 #ifdef DEBUG
 326             printf ("   Distance is oscillating -- dst flag nixes struct!\n");
 327 #endif
 328                 return BAD_STRUCT_TM;
 329               }
 330
 331 #ifdef DEBUG
 332             printf ("   Distance is oscillating -- chose the later time.\n");
 333 #endif
 334             distance = 0;
 335           }
 336
 337         if ((distance == 0) && (me->tm_isdst != -1)
 338             && (me->tm_isdst != guess_tm->tm_isdst))
 339           {
 340             /* If we're in this code, we've got the right time but the
 341                wrong daylight savings flag.  We need to move away from
 342                the time that we have and approach the other time from
 343                the other direction.  That is, if I've requested the
 344                non-DST version of a time and I get the DST version
 345                instead, I want to put us forward in time and search
 346                backwards to get the other time.  I checked all of the
 347                configuration files for the tz package -- no entry
 348                saves more than two hours, so I think we'll be safe by
 349                moving 24 hours in one direction.  IF THE AMOUNT OF
 350                TIME SAVED IN THE CONFIGURATION FILES CHANGES, THIS
 351                VALUE MAY NEED TO BE ADJUSTED.  Luckily, we can never
 352                have more than one level of overlaps, or this would
 353                never work. */
 354
 355 #define SKIP_VALUE 86400
 356
 357             if (guess_tm->tm_isdst == 0)
 358               /* we got the later one, but want the earlier one */
 359               distance = -SKIP_VALUE;
 360             else
 361               distance = SKIP_VALUE;
 362
 363 #ifdef DEBUG
 364             printf ("   Got the right time, wrong DST value -- adjusting\n");
 365 #endif
 366           }
 367
 368         last_distance = distance;
 369
 370       } while (distance != 0);
 371
 372     /* Check to see that the dst flag matches */
 373
 374     if (me->tm_isdst != -1)
 375       {
 376         if (me->tm_isdst != guess_tm->tm_isdst)
 377           {
 378 #ifdef DEBUG
 379             printf ("   DST flag doesn't match!  FIXME?\n");
 380 #endif
 381             return BAD_STRUCT_TM;
 382           }
 383       }
 384
 385     result = guess;             /* Success! */
 386
 387     /* On successful completion, the values of tm_wday and tm_yday
 388        have to be set appropriately. */
 389
 390     /* me->tm_yday = guess_tm->tm_yday;
 391        me->tm_mday = guess_tm->tm_mday; */
 392
 393     *me = *guess_tm;
 394   }
 395
 396   /* Update the caller's version of the structure */
 397
 398   *timeptr = *me;
 399
 400   return result;
 401 }
 402
 403 time_t
 404 #ifdef DEBUG                    /* make it work even if the system's
 405                                    libc has it's own mktime routine */
 406 my_mktime (timeptr)
 407 #else
 408 mktime (timeptr)
 409 #endif
 410      struct tm *timeptr;
 411 {
 412   return _mktime_internal (timeptr, localtime);
 413 }
 414 \f
 415 #ifdef DEBUG
 416 void
 417 main (argc, argv)
 418      int argc;
 419      char *argv[];
 420 {
 421   int time;
 422   int result_time;
 423   struct tm *tmptr;
 424
 425   if (argc == 1)
 426     {
 427       long q;
 428
 429       printf ("starting long test...\n");
 430
 431       for (q = 10000000; q < 1000000000; q += 599)
 432         {
 433           struct tm *tm = localtime ((time_t *) &q);
 434           if ((q % 10000) == 0) { printf ("%ld\n", q); fflush (stdout); }
 435           if (q != my_mktime (tm))
 436             { printf ("failed for %ld\n", q); fflush (stdout); }
 437         }
 438
 439       printf ("test finished\n");
 440
 441       exit (0);
 442     }
 443
 444   if (argc != 2)
 445     {
 446       printf ("wrong # of args\n");
 447       exit (0);
 448     }
 449
 450   debugging_enabled = 1;        /* We want to see the info */
 451
 452   ++argv;
 453   time = atoi (*argv);
 454
 455   tmptr = localtime ((time_t *) &time);
 456   printf ("Localtime tells us that a time_t of %d represents\n     ", time);
 457   printtm (tmptr);
 458   putchar ('\n');
 459
 460   printf ("   Given localtime's return val, mktime returns %d which is\n     ",
 461           (int) my_mktime (tmptr));
 462   printtm (tmptr);
 463   putchar ('\n');
 464
 465 #if 0
 466   tmptr->tm_sec -= 20;
 467   tmptr->tm_min -= 20;
 468   tmptr->tm_hour -= 20;
 469   tmptr->tm_mday -= 20;
 470   tmptr->tm_mon -= 20;
 471   tmptr->tm_year -= 20;
 472   tmptr->tm_gmtoff -= 20000;    /* This has no effect! */
 473   tmptr->tm_zone = NULL;        /* Nor does this! */
 474   tmptr->tm_isdst = -1;
 475 #endif
 476
 477   tmptr->tm_hour += 1;
 478   tmptr->tm_isdst = -1;
 479
 480   printf ("\n\nchanged ranges: ");
 481   printtm (tmptr);
 482   putchar ('\n');
 483
 484   result_time = my_mktime (tmptr);
 485   printf ("\nmktime: %d\n", result_time);
 486
 487   tmptr->tm_isdst = 0;
 488
 489   printf ("\n\nchanged ranges: ");
 490   printtm (tmptr);
 491   putchar ('\n');
 492
 493   result_time = my_mktime (tmptr);
 494   printf ("\nmktime: %d\n", result_time);
 495 }
 496 #endif /* DEBUG */
 497
 498 \f
 499 /*
 500 Local Variables:
 501 compile-command: "gcc -g mktime.c -o mktime -DDEBUG"
 502 End:
 503 */