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