time/tzset.c

   1 /* Copyright (C) 1991,92,93,94,95,96,97,98 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <ctype.h>
  20 #include <errno.h>
  21 #include <bits/libc-lock.h>
  22 #include <stddef.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <time.h>
  27
  28 /* Defined in mktime.c.  */
  29 extern const unsigned short int __mon_yday[2][13];
  30
  31 /* Defined in localtime.c.  */
  32 extern struct tm _tmbuf;
  33
  34 #define NOID
  35 #include <timezone/tzfile.h>
  36
  37 extern int __use_tzfile;
  38 extern void __tzfile_read __P ((const char *file));
  39 extern int __tzfile_compute __P ((time_t timer, int use_localtime,
  40                                   long int *leap_correct, int *leap_hit,
  41                                   struct tm *tp));
  42 extern void __tzfile_default __P ((const char *std, const char *dst,
  43                                    long int stdoff, long int dstoff));
  44 extern char *__tzstring __P ((const char *string));
  45
  46 char *__tzname[2] = { (char *) "GMT", (char *) "GMT" };
  47 int __daylight = 0;
  48 long int __timezone = 0L;
  49
  50 weak_alias (__tzname, tzname)
  51 weak_alias (__daylight, daylight)
  52 weak_alias (__timezone, timezone)
  53
  54 /* This locks all the state variables in tzfile.c and this file.  */
  55 __libc_lock_define (static, tzset_lock)
  56
  57
  58 #define min(a, b)       ((a) < (b) ? (a) : (b))
  59 #define max(a, b)       ((a) > (b) ? (a) : (b))
  60 #define sign(x)         ((x) < 0 ? -1 : 1)
  61
  62
  63 /* This structure contains all the information about a
  64    timezone given in the POSIX standard TZ envariable.  */
  65 typedef struct
  66   {
  67     const char *name;
  68
  69     /* When to change.  */
  70     enum { J0, J1, M } type;    /* Interpretation of:  */
  71     unsigned short int m, n, d; /* Month, week, day.  */
  72     unsigned int secs;          /* Time of day.  */
  73
  74     long int offset;            /* Seconds east of GMT (west if < 0).  */
  75
  76     /* We cache the computed time of change for a
  77        given year so we don't have to recompute it.  */
  78     time_t change;      /* When to change to this zone.  */
  79     int computed_for;   /* Year above is computed for.  */
  80   } tz_rule;
  81
  82 /* tz_rules[0] is standard, tz_rules[1] is daylight.  */
  83 static tz_rule tz_rules[2];
  84
  85
  86 static int compute_change __P ((tz_rule *rule, int year)) internal_function;
  87 static int tz_compute __P ((time_t timer, const struct tm *tm))
  88      internal_function;
  89 static void tzset_internal __P ((int always)) internal_function;
  90 \f
  91 /* Header for a list of buffers containing time zone strings.  */
  92 struct tzstring_head
  93 {
  94   struct tzstring_head *next;
  95   /* The buffer itself immediately follows the header.
  96      The buffer contains zero or more (possibly overlapping) strings.
  97      The last string is followed by 2 '\0's instead of the usual 1.  */
  98 };
  99
 100 /* First in a list of buffers containing time zone strings.
 101    All the buffers but the last are read-only.  */
 102 static struct
 103 {
 104   struct tzstring_head head;
 105   char data[48];
 106 } tzstring_list;
 107
 108 /* Size of the last buffer in the list, not counting its header.  */
 109 static size_t tzstring_last_buffer_size = sizeof tzstring_list.data;
 110
 111 /* Allocate a time zone string with given contents.
 112    The string will never be moved or deallocated.
 113    However, its contents may be shared with other such strings.  */
 114 char *
 115 __tzstring (string)
 116      const char *string;
 117 {
 118   struct tzstring_head *h;
 119   size_t needed;
 120   char *p;
 121
 122   /* Look through time zone string list for a duplicate of this one.  */
 123   for (h = &tzstring_list.head;  ;  h = h->next)
 124     {
 125       for (p = (char *) (h + 1);  p[0] | p[1];  ++p)
 126         if (strcmp (p, string) == 0)
 127           return p;
 128       if (! h->next)
 129         break;
 130     }
 131
 132   /* No duplicate was found.  Copy to the end of this buffer if there's room;
 133      otherwise, append a large-enough new buffer to the list and use it.  */
 134   ++p;
 135   needed = strlen (string) + 2; /* Need 2 trailing '\0's after last string.  */
 136
 137   if ((size_t) ((char *) (h + 1) + tzstring_last_buffer_size - p) < needed)
 138     {
 139       size_t buffer_size = tzstring_last_buffer_size;
 140       while ((buffer_size *= 2) < needed)
 141         continue;
 142       h = malloc (sizeof *h + buffer_size);
 143       if (h == NULL)
 144         return NULL;
 145       h->next = NULL;
 146       tzstring_last_buffer_size = buffer_size;
 147       p = (char *) (h + 1);
 148     }
 149
 150   return strncpy (p, string, needed);
 151 }
 152 \f
 153 static char *old_tz = NULL;
 154
 155 /* Interpret the TZ envariable.  */
 156 static void
 157 internal_function
 158 tzset_internal (always)
 159      int always;
 160 {
 161   static int is_initialized = 0;
 162   register const char *tz;
 163   register size_t l;
 164   char *tzbuf;
 165   unsigned short int hh, mm, ss;
 166   unsigned short int whichrule;
 167
 168   if (is_initialized && !always)
 169     return;
 170   is_initialized = 1;
 171
 172   /* Examine the TZ environment variable.  */
 173   tz = getenv ("TZ");
 174   if (tz == NULL)
 175     /* No user specification; use the site-wide default.  */
 176     tz = TZDEFAULT;
 177   else if (*tz == '\0')
 178     /* User specified the empty string; use UTC explicitly.  */
 179     tz = "Universal";
 180
 181   /* A leading colon means "implementation defined syntax".
 182      We ignore the colon and always use the same algorithm:
 183      try a data file, and if none exists parse the 1003.1 syntax.  */
 184   if (tz && *tz == ':')
 185     ++tz;
 186
 187   /* Check whether the value changes since the last run.  */
 188   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 189     /* No change, simply return.  */
 190     return;
 191
 192   tz_rules[0].name = NULL;
 193   tz_rules[1].name = NULL;
 194
 195   /* Save the value of `tz'.  */
 196   if (old_tz != NULL)
 197     free (old_tz);
 198   old_tz = tz ? __strdup (tz) : NULL;
 199
 200   /* Try to read a data file.  */
 201   __tzfile_read (tz);
 202   if (__use_tzfile)
 203     return;
 204
 205   /* No data file found.  Default to UTC if nothing specified.  */
 206
 207   if (tz == NULL || *tz == '\0')
 208     {
 209       tz_rules[0].name = tz_rules[1].name = "UTC";
 210       tz_rules[0].type = tz_rules[1].type = J0;
 211       tz_rules[0].m = tz_rules[0].n = tz_rules[0].d = 0;
 212       tz_rules[1].m = tz_rules[1].n = tz_rules[1].d = 0;
 213       tz_rules[0].secs = tz_rules[1].secs = 0;
 214       tz_rules[0].offset = tz_rules[1].offset = 0L;
 215       tz_rules[0].change = tz_rules[1].change = (time_t) -1;
 216       tz_rules[0].computed_for = tz_rules[1].computed_for = 0;
 217       return;
 218     }
 219
 220   /* Clear out old state and reset to unnamed UTC.  */
 221   memset (tz_rules, 0, sizeof tz_rules);
 222   tz_rules[0].name = tz_rules[1].name = "";
 223
 224   /* Get the standard timezone name.  */
 225   tzbuf = malloc (strlen (tz) + 1);
 226   if (! tzbuf)
 227     {
 228       /* Clear the old tz name so we will try again.  */
 229       free (old_tz);
 230       old_tz = NULL;
 231       return;
 232     }
 233
 234   if (sscanf (tz, "%[^0-9,+-]", tzbuf) != 1 ||
 235       (l = strlen (tzbuf)) < 3)
 236     {
 237       free (tzbuf);
 238       return;
 239     }
 240
 241   tz_rules[0].name = __tzstring (tzbuf);
 242
 243   tz += l;
 244
 245   /* Figure out the standard offset from UTC.  */
 246   if (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz)))
 247     {
 248       free (tzbuf);
 249       return;
 250     }
 251
 252   if (*tz == '-' || *tz == '+')
 253     tz_rules[0].offset = *tz++ == '-' ? 1L : -1L;
 254   else
 255     tz_rules[0].offset = -1L;
 256   switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 257     {
 258     default:
 259       free (tzbuf);
 260       return;
 261     case 1:
 262       mm = 0;
 263     case 2:
 264       ss = 0;
 265     case 3:
 266       break;
 267     }
 268   tz_rules[0].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 269                          (min (hh, 23) * 60 * 60));
 270
 271   for (l = 0; l < 3; ++l)
 272     {
 273       while (isdigit(*tz))
 274         ++tz;
 275       if (l < 2 && *tz == ':')
 276         ++tz;
 277     }
 278
 279   /* Get the DST timezone name (if any).  */
 280   if (*tz != '\0')
 281     {
 282       char *n = tzbuf + strlen (tzbuf) + 1;
 283       if (sscanf (tz, "%[^0-9,+-]", n) != 1 ||
 284           (l = strlen (n)) < 3)
 285         goto done_names;        /* Punt on name, set up the offsets.  */
 286
 287       tz_rules[1].name = __tzstring (n);
 288
 289       tz += l;
 290
 291       /* Figure out the DST offset from GMT.  */
 292       if (*tz == '-' || *tz == '+')
 293         tz_rules[1].offset = *tz++ == '-' ? 1L : -1L;
 294       else
 295         tz_rules[1].offset = -1L;
 296
 297       switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 298         {
 299         default:
 300           /* Default to one hour later than standard time.  */
 301           tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 302           break;
 303
 304         case 1:
 305           mm = 0;
 306         case 2:
 307           ss = 0;
 308         case 3:
 309           tz_rules[1].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 310                                  (min (hh, 23) * (60 * 60)));
 311           break;
 312         }
 313       for (l = 0; l < 3; ++l)
 314         {
 315           while (isdigit (*tz))
 316             ++tz;
 317           if (l < 2 && *tz == ':')
 318             ++tz;
 319         }
 320       if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 321         {
 322           /* There is no rule.  See if there is a default rule file.  */
 323           __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 324                             tz_rules[0].offset, tz_rules[1].offset);
 325           if (__use_tzfile)
 326             {
 327               free (old_tz);
 328               old_tz = NULL;
 329               free (tzbuf);
 330               return;
 331             }
 332         }
 333     }
 334   else
 335     {
 336       /* There is no DST.  */
 337       tz_rules[1].name = tz_rules[0].name;
 338       tz_rules[1].offset = tz_rules[0].offset;
 339       free (tzbuf);
 340       return;
 341     }
 342
 343  done_names:
 344   free (tzbuf);
 345
 346   /* Figure out the standard <-> DST rules.  */
 347   for (whichrule = 0; whichrule < 2; ++whichrule)
 348     {
 349       register tz_rule *tzr = &tz_rules[whichrule];
 350
 351       /* Ignore comma to support string following the incorrect
 352          specification in early POSIX.1 printings.  */
 353       tz += *tz == ',';
 354
 355       /* Get the date of the change.  */
 356       if (*tz == 'J' || isdigit (*tz))
 357         {
 358           char *end;
 359           tzr->type = *tz == 'J' ? J1 : J0;
 360           if (tzr->type == J1 && !isdigit (*++tz))
 361             return;
 362           tzr->d = (unsigned short int) strtoul (tz, &end, 10);
 363           if (end == tz || tzr->d > 365)
 364             return;
 365           else if (tzr->type == J1 && tzr->d == 0)
 366             return;
 367           tz = end;
 368         }
 369       else if (*tz == 'M')
 370         {
 371           int n;
 372           tzr->type = M;
 373           if (sscanf (tz, "M%hu.%hu.%hu%n",
 374                       &tzr->m, &tzr->n, &tzr->d, &n) != 3 ||
 375               tzr->m < 1 || tzr->m > 12 ||
 376               tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 377             return;
 378           tz += n;
 379         }
 380       else if (*tz == '\0')
 381         {
 382           /* United States Federal Law, the equivalent of "M4.1.0,M10.5.0".  */
 383           tzr->type = M;
 384           if (tzr == &tz_rules[0])
 385             {
 386               tzr->m = 4;
 387               tzr->n = 1;
 388               tzr->d = 0;
 389             }
 390           else
 391             {
 392               tzr->m = 10;
 393               tzr->n = 5;
 394               tzr->d = 0;
 395             }
 396         }
 397       else
 398         return;
 399
 400       if (*tz != '\0' && *tz != '/' && *tz != ',')
 401         return;
 402       else if (*tz == '/')
 403         {
 404           /* Get the time of day of the change.  */
 405           ++tz;
 406           if (*tz == '\0')
 407             return;
 408           switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 409             {
 410             default:
 411               hh = 2;           /* Default to 2:00 AM.  */
 412             case 1:
 413               mm = 0;
 414             case 2:
 415               ss = 0;
 416             case 3:
 417               break;
 418             }
 419           for (l = 0; l < 3; ++l)
 420             {
 421               while (isdigit (*tz))
 422                 ++tz;
 423               if (l < 2 && *tz == ':')
 424                 ++tz;
 425             }
 426           tzr->secs = (hh * 60 * 60) + (mm * 60) + ss;
 427         }
 428       else
 429         /* Default to 2:00 AM.  */
 430         tzr->secs = 2 * 60 * 60;
 431
 432       tzr->computed_for = -1;
 433     }
 434 }
 435 \f
 436 /* Maximum length of a timezone name.  __tz_compute keeps this up to date
 437    (never decreasing it) when ! __use_tzfile.
 438    tzfile.c keeps it up to date when __use_tzfile.  */
 439 size_t __tzname_cur_max;
 440
 441 long int
 442 __tzname_max ()
 443 {
 444   __libc_lock_lock (tzset_lock);
 445
 446   tzset_internal (0);
 447
 448   __libc_lock_unlock (tzset_lock);
 449
 450   return __tzname_cur_max;
 451 }
 452 \f
 453 /* Figure out the exact time (as a time_t) in YEAR
 454    when the change described by RULE will occur and
 455    put it in RULE->change, saving YEAR in RULE->computed_for.
 456    Return nonzero if successful, zero on failure.  */
 457 static int
 458 internal_function
 459 compute_change (rule, year)
 460      tz_rule *rule;
 461      int year;
 462 {
 463   register time_t t;
 464   int y;
 465
 466   if (year != -1 && rule->computed_for == year)
 467     /* Operations on times in 1969 will be slower.  Oh well.  */
 468     return 1;
 469
 470   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 471   t = 0;
 472   for (y = 1970; y < year; ++y)
 473     t += SECSPERDAY * (__isleap (y) ? 366 : 365);
 474
 475   switch (rule->type)
 476     {
 477     case J1:
 478       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 479          In non-leap years, or if the day number is 59 or less, just
 480          add SECSPERDAY times the day number-1 to the time of
 481          January 1, midnight, to get the day.  */
 482       t += (rule->d - 1) * SECSPERDAY;
 483       if (rule->d >= 60 && __isleap (year))
 484         t += SECSPERDAY;
 485       break;
 486
 487     case J0:
 488       /* n - Day of year.
 489          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 490       t += rule->d * SECSPERDAY;
 491       break;
 492
 493     case M:
 494       /* Mm.n.d - Nth "Dth day" of month M.  */
 495       {
 496         unsigned int i;
 497         int d, m1, yy0, yy1, yy2, dow;
 498         const unsigned short int *myday =
 499           &__mon_yday[__isleap (year)][rule->m];
 500
 501         /* First add SECSPERDAY for each day in months before M.  */
 502         t += myday[-1] * SECSPERDAY;
 503
 504         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 505         m1 = (rule->m + 9) % 12 + 1;
 506         yy0 = (rule->m <= 2) ? (year - 1) : year;
 507         yy1 = yy0 / 100;
 508         yy2 = yy0 % 100;
 509         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 510         if (dow < 0)
 511           dow += 7;
 512
 513         /* DOW is the day-of-week of the first day of the month.  Get the
 514            day-of-month (zero-origin) of the first DOW day of the month.  */
 515         d = rule->d - dow;
 516         if (d < 0)
 517           d += 7;
 518         for (i = 1; i < rule->n; ++i)
 519           {
 520             if (d + 7 >= (int) myday[0] - myday[-1])
 521               break;
 522             d += 7;
 523           }
 524
 525         /* D is the day-of-month (zero-origin) of the day we want.  */
 526         t += d * SECSPERDAY;
 527       }
 528       break;
 529     }
 530
 531   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 532      Just add the time of day and local offset from GMT, and we're done.  */
 533
 534   rule->change = t - rule->offset + rule->secs;
 535   rule->computed_for = year;
 536   return 1;
 537 }
 538
 539
 540 /* Figure out the correct timezone for *TIMER and TM (which must be the same)
 541    and set `__tzname', `__timezone', and `__daylight' accordingly.
 542    Return nonzero on success, zero on failure.  */
 543 static int
 544 internal_function
 545 tz_compute (timer, tm)
 546      time_t timer;
 547      const struct tm *tm;
 548 {
 549   if (! compute_change (&tz_rules[0], 1900 + tm->tm_year) ||
 550       ! compute_change (&tz_rules[1], 1900 + tm->tm_year))
 551     return 0;
 552
 553   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 554   __timezone = -tz_rules[0].offset;
 555   __tzname[0] = (char *) tz_rules[0].name;
 556   __tzname[1] = (char *) tz_rules[1].name;
 557
 558   {
 559     /* Keep __tzname_cur_max up to date.  */
 560     size_t len0 = strlen (__tzname[0]);
 561     size_t len1 = strlen (__tzname[1]);
 562     if (len0 > __tzname_cur_max)
 563       __tzname_cur_max = len0;
 564     if (len1 > __tzname_cur_max)
 565       __tzname_cur_max = len1;
 566   }
 567
 568   return 1;
 569 }
 570 \f
 571 /* Reinterpret the TZ environment variable and set `tzname'.  */
 572 #undef tzset
 573
 574 void
 575 __tzset (void)
 576 {
 577   __libc_lock_lock (tzset_lock);
 578
 579   tzset_internal (1);
 580
 581   if (!__use_tzfile)
 582     {
 583       /* Set `tzname'.  */
 584       __tzname[0] = (char *) tz_rules[0].name;
 585       __tzname[1] = (char *) tz_rules[1].name;
 586     }
 587
 588   __libc_lock_unlock (tzset_lock);
 589 }
 590 weak_alias (__tzset, tzset)
 591 \f
 592 /* Return the `struct tm' representation of *TIMER in the local timezone.
 593    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 594 struct tm *
 595 __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
 596 {
 597   long int leap_correction;
 598   int leap_extra_secs;
 599
 600   if (timer == NULL)
 601     {
 602       __set_errno (EINVAL);
 603       return NULL;
 604     }
 605
 606   __libc_lock_lock (tzset_lock);
 607
 608   /* Update internal database according to current TZ setting.
 609      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 610      This is a good idea since this allows at least a bit more parallelism.
 611      By analogy we apply the same rule to gmtime_r.  */
 612   tzset_internal (tp == &_tmbuf);
 613
 614   if (__use_tzfile)
 615     {
 616       if (! __tzfile_compute (*timer, use_localtime,
 617                               &leap_correction, &leap_extra_secs, tp))
 618         tp = NULL;
 619     }
 620   else
 621     {
 622       if (! (__offtime (timer, 0, tp) && tz_compute (*timer, tp)))
 623         tp = NULL;
 624       leap_correction = 0L;
 625       leap_extra_secs = 0;
 626     }
 627
 628   if (tp)
 629     {
 630       if (use_localtime)
 631         {
 632           if (!__use_tzfile)
 633             {
 634               int isdst = (*timer >= tz_rules[0].change
 635                            && *timer < tz_rules[1].change);
 636               tp->tm_isdst = isdst;
 637               tp->tm_zone = __tzname[isdst];
 638               tp->tm_gmtoff = tz_rules[isdst].offset;
 639             }
 640         }
 641       else
 642         {
 643           tp->tm_isdst = 0;
 644           tp->tm_zone = "GMT";
 645           tp->tm_gmtoff = 0L;
 646         }
 647
 648       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 649         tp->tm_sec += leap_extra_secs;
 650       else
 651         tp = NULL;
 652     }
 653
 654   __libc_lock_unlock (tzset_lock);
 655
 656   return tp;
 657 }