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 /* List of buffers containing time zone strings. */
  92 struct tzstring_l
  93 {
  94   struct tzstring_l *next;
  95   size_t len;  /* strlen(data) - doesn't count terminating NUL! */
  96   char data[0];
  97 };
  98
  99 struct tzstring_l *tzstring_list;
 100
 101 /* Allocate a permanent home for S.  It will never be moved or deallocated,
 102    but may share space with other strings.
 103    Don't modify the returned string. */
 104 char *
 105 __tzstring (const char *s)
 106 {
 107   char *p;
 108   struct tzstring_l *t, *u, *new;
 109   size_t len = strlen(s);
 110
 111   /* Walk the list and look for a match.  If this string is the same
 112      as the end of an already-allocated string, it can share space. */
 113   for (u = t = tzstring_list; t; u = t, t = t->next)
 114     if (len <= t->len)
 115       {
 116         p = &t->data[t->len - len];
 117         if (strcmp (s, p) == 0)
 118           return p;
 119       }
 120
 121   /* Not found; allocate a new buffer. */
 122   new = malloc (sizeof (struct tzstring_l) + len + 1);
 123   if (!new)
 124     return NULL;
 125
 126   new->next = NULL;
 127   new->len = len;
 128   strcpy (new->data, s);
 129
 130   if (u)
 131     u->next = new;
 132   else
 133     tzstring_list = new;
 134
 135   return new->data;
 136 }
 137 \f
 138 static char *old_tz = NULL;
 139
 140 /* Interpret the TZ envariable.  */
 141 static void
 142 internal_function
 143 tzset_internal (always)
 144      int always;
 145 {
 146   static int is_initialized = 0;
 147   register const char *tz;
 148   register size_t l;
 149   char *tzbuf;
 150   unsigned short int hh, mm, ss;
 151   unsigned short int whichrule;
 152
 153   if (is_initialized && !always)
 154     return;
 155   is_initialized = 1;
 156
 157   /* Examine the TZ environment variable.  */
 158   tz = getenv ("TZ");
 159   if (tz == NULL)
 160     /* No user specification; use the site-wide default.  */
 161     tz = TZDEFAULT;
 162   else if (*tz == '\0')
 163     /* User specified the empty string; use UTC explicitly.  */
 164     tz = "Universal";
 165
 166   /* A leading colon means "implementation defined syntax".
 167      We ignore the colon and always use the same algorithm:
 168      try a data file, and if none exists parse the 1003.1 syntax.  */
 169   if (tz && *tz == ':')
 170     ++tz;
 171
 172   /* Check whether the value changes since the last run.  */
 173   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 174     /* No change, simply return.  */
 175     return;
 176
 177   tz_rules[0].name = NULL;
 178   tz_rules[1].name = NULL;
 179
 180   /* Save the value of `tz'.  */
 181   if (old_tz != NULL)
 182     free (old_tz);
 183   old_tz = tz ? __strdup (tz) : NULL;
 184
 185   /* Try to read a data file.  */
 186   __tzfile_read (tz);
 187   if (__use_tzfile)
 188     return;
 189
 190   /* No data file found.  Default to UTC if nothing specified.  */
 191
 192   if (tz == NULL || *tz == '\0')
 193     {
 194       tz_rules[0].name = tz_rules[1].name = "UTC";
 195       tz_rules[0].type = tz_rules[1].type = J0;
 196       tz_rules[0].m = tz_rules[0].n = tz_rules[0].d = 0;
 197       tz_rules[1].m = tz_rules[1].n = tz_rules[1].d = 0;
 198       tz_rules[0].secs = tz_rules[1].secs = 0;
 199       tz_rules[0].offset = tz_rules[1].offset = 0L;
 200       tz_rules[0].change = tz_rules[1].change = (time_t) -1;
 201       tz_rules[0].computed_for = tz_rules[1].computed_for = 0;
 202       return;
 203     }
 204
 205   /* Clear out old state and reset to unnamed UTC.  */
 206   memset (tz_rules, 0, sizeof tz_rules);
 207   tz_rules[0].name = tz_rules[1].name = "";
 208
 209   /* Get the standard timezone name.  */
 210   tzbuf = malloc (strlen (tz) + 1);
 211   if (! tzbuf)
 212     {
 213       /* Clear the old tz name so we will try again.  */
 214       free (old_tz);
 215       old_tz = NULL;
 216       return;
 217     }
 218
 219   if (sscanf (tz, "%[^0-9,+-]", tzbuf) != 1 ||
 220       (l = strlen (tzbuf)) < 3)
 221     {
 222       free (tzbuf);
 223       return;
 224     }
 225
 226   tz_rules[0].name = __tzstring (tzbuf);
 227
 228   tz += l;
 229
 230   /* Figure out the standard offset from UTC.  */
 231   if (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz)))
 232     {
 233       free (tzbuf);
 234       return;
 235     }
 236
 237   if (*tz == '-' || *tz == '+')
 238     tz_rules[0].offset = *tz++ == '-' ? 1L : -1L;
 239   else
 240     tz_rules[0].offset = -1L;
 241   switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 242     {
 243     default:
 244       free (tzbuf);
 245       return;
 246     case 1:
 247       mm = 0;
 248     case 2:
 249       ss = 0;
 250     case 3:
 251       break;
 252     }
 253   tz_rules[0].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 254                          (min (hh, 23) * 60 * 60));
 255
 256   for (l = 0; l < 3; ++l)
 257     {
 258       while (isdigit(*tz))
 259         ++tz;
 260       if (l < 2 && *tz == ':')
 261         ++tz;
 262     }
 263
 264   /* Get the DST timezone name (if any).  */
 265   if (*tz != '\0')
 266     {
 267       char *n = tzbuf + strlen (tzbuf) + 1;
 268       if (sscanf (tz, "%[^0-9,+-]", n) != 1 ||
 269           (l = strlen (n)) < 3)
 270         goto done_names;        /* Punt on name, set up the offsets.  */
 271
 272       tz_rules[1].name = __tzstring (n);
 273
 274       tz += l;
 275
 276       /* Figure out the DST offset from GMT.  */
 277       if (*tz == '-' || *tz == '+')
 278         tz_rules[1].offset = *tz++ == '-' ? 1L : -1L;
 279       else
 280         tz_rules[1].offset = -1L;
 281
 282       switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 283         {
 284         default:
 285           /* Default to one hour later than standard time.  */
 286           tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 287           break;
 288
 289         case 1:
 290           mm = 0;
 291         case 2:
 292           ss = 0;
 293         case 3:
 294           tz_rules[1].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 295                                  (min (hh, 23) * (60 * 60)));
 296           break;
 297         }
 298       for (l = 0; l < 3; ++l)
 299         {
 300           while (isdigit (*tz))
 301             ++tz;
 302           if (l < 2 && *tz == ':')
 303             ++tz;
 304         }
 305       if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 306         {
 307           /* There is no rule.  See if there is a default rule file.  */
 308           __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 309                             tz_rules[0].offset, tz_rules[1].offset);
 310           if (__use_tzfile)
 311             {
 312               free (old_tz);
 313               old_tz = NULL;
 314               free (tzbuf);
 315               return;
 316             }
 317         }
 318     }
 319   else
 320     {
 321       /* There is no DST.  */
 322       tz_rules[1].name = tz_rules[0].name;
 323       tz_rules[1].offset = tz_rules[0].offset;
 324       free (tzbuf);
 325       return;
 326     }
 327
 328  done_names:
 329   free (tzbuf);
 330
 331   /* Figure out the standard <-> DST rules.  */
 332   for (whichrule = 0; whichrule < 2; ++whichrule)
 333     {
 334       register tz_rule *tzr = &tz_rules[whichrule];
 335
 336       /* Ignore comma to support string following the incorrect
 337          specification in early POSIX.1 printings.  */
 338       tz += *tz == ',';
 339
 340       /* Get the date of the change.  */
 341       if (*tz == 'J' || isdigit (*tz))
 342         {
 343           char *end;
 344           tzr->type = *tz == 'J' ? J1 : J0;
 345           if (tzr->type == J1 && !isdigit (*++tz))
 346             return;
 347           tzr->d = (unsigned short int) strtoul (tz, &end, 10);
 348           if (end == tz || tzr->d > 365)
 349             return;
 350           else if (tzr->type == J1 && tzr->d == 0)
 351             return;
 352           tz = end;
 353         }
 354       else if (*tz == 'M')
 355         {
 356           int n;
 357           tzr->type = M;
 358           if (sscanf (tz, "M%hu.%hu.%hu%n",
 359                       &tzr->m, &tzr->n, &tzr->d, &n) != 3 ||
 360               tzr->m < 1 || tzr->m > 12 ||
 361               tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 362             return;
 363           tz += n;
 364         }
 365       else if (*tz == '\0')
 366         {
 367           /* United States Federal Law, the equivalent of "M4.1.0,M10.5.0".  */
 368           tzr->type = M;
 369           if (tzr == &tz_rules[0])
 370             {
 371               tzr->m = 4;
 372               tzr->n = 1;
 373               tzr->d = 0;
 374             }
 375           else
 376             {
 377               tzr->m = 10;
 378               tzr->n = 5;
 379               tzr->d = 0;
 380             }
 381         }
 382       else
 383         return;
 384
 385       if (*tz != '\0' && *tz != '/' && *tz != ',')
 386         return;
 387       else if (*tz == '/')
 388         {
 389           /* Get the time of day of the change.  */
 390           ++tz;
 391           if (*tz == '\0')
 392             return;
 393           switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 394             {
 395             default:
 396               hh = 2;           /* Default to 2:00 AM.  */
 397             case 1:
 398               mm = 0;
 399             case 2:
 400               ss = 0;
 401             case 3:
 402               break;
 403             }
 404           for (l = 0; l < 3; ++l)
 405             {
 406               while (isdigit (*tz))
 407                 ++tz;
 408               if (l < 2 && *tz == ':')
 409                 ++tz;
 410             }
 411           tzr->secs = (hh * 60 * 60) + (mm * 60) + ss;
 412         }
 413       else
 414         /* Default to 2:00 AM.  */
 415         tzr->secs = 2 * 60 * 60;
 416
 417       tzr->computed_for = -1;
 418     }
 419 }
 420 \f
 421 /* Maximum length of a timezone name.  __tz_compute keeps this up to date
 422    (never decreasing it) when ! __use_tzfile.
 423    tzfile.c keeps it up to date when __use_tzfile.  */
 424 size_t __tzname_cur_max;
 425
 426 long int
 427 __tzname_max ()
 428 {
 429   __libc_lock_lock (tzset_lock);
 430
 431   tzset_internal (0);
 432
 433   __libc_lock_unlock (tzset_lock);
 434
 435   return __tzname_cur_max;
 436 }
 437 \f
 438 /* Figure out the exact time (as a time_t) in YEAR
 439    when the change described by RULE will occur and
 440    put it in RULE->change, saving YEAR in RULE->computed_for.
 441    Return nonzero if successful, zero on failure.  */
 442 static int
 443 internal_function
 444 compute_change (rule, year)
 445      tz_rule *rule;
 446      int year;
 447 {
 448   register time_t t;
 449   int y;
 450
 451   if (year != -1 && rule->computed_for == year)
 452     /* Operations on times in 1969 will be slower.  Oh well.  */
 453     return 1;
 454
 455   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 456   t = 0;
 457   for (y = 1970; y < year; ++y)
 458     t += SECSPERDAY * (__isleap (y) ? 366 : 365);
 459
 460   switch (rule->type)
 461     {
 462     case J1:
 463       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 464          In non-leap years, or if the day number is 59 or less, just
 465          add SECSPERDAY times the day number-1 to the time of
 466          January 1, midnight, to get the day.  */
 467       t += (rule->d - 1) * SECSPERDAY;
 468       if (rule->d >= 60 && __isleap (year))
 469         t += SECSPERDAY;
 470       break;
 471
 472     case J0:
 473       /* n - Day of year.
 474          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 475       t += rule->d * SECSPERDAY;
 476       break;
 477
 478     case M:
 479       /* Mm.n.d - Nth "Dth day" of month M.  */
 480       {
 481         unsigned int i;
 482         int d, m1, yy0, yy1, yy2, dow;
 483         const unsigned short int *myday =
 484           &__mon_yday[__isleap (year)][rule->m];
 485
 486         /* First add SECSPERDAY for each day in months before M.  */
 487         t += myday[-1] * SECSPERDAY;
 488
 489         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 490         m1 = (rule->m + 9) % 12 + 1;
 491         yy0 = (rule->m <= 2) ? (year - 1) : year;
 492         yy1 = yy0 / 100;
 493         yy2 = yy0 % 100;
 494         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 495         if (dow < 0)
 496           dow += 7;
 497
 498         /* DOW is the day-of-week of the first day of the month.  Get the
 499            day-of-month (zero-origin) of the first DOW day of the month.  */
 500         d = rule->d - dow;
 501         if (d < 0)
 502           d += 7;
 503         for (i = 1; i < rule->n; ++i)
 504           {
 505             if (d + 7 >= (int) myday[0] - myday[-1])
 506               break;
 507             d += 7;
 508           }
 509
 510         /* D is the day-of-month (zero-origin) of the day we want.  */
 511         t += d * SECSPERDAY;
 512       }
 513       break;
 514     }
 515
 516   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 517      Just add the time of day and local offset from GMT, and we're done.  */
 518
 519   rule->change = t - rule->offset + rule->secs;
 520   rule->computed_for = year;
 521   return 1;
 522 }
 523
 524
 525 /* Figure out the correct timezone for *TIMER and TM (which must be the same)
 526    and set `__tzname', `__timezone', and `__daylight' accordingly.
 527    Return nonzero on success, zero on failure.  */
 528 static int
 529 internal_function
 530 tz_compute (timer, tm)
 531      time_t timer;
 532      const struct tm *tm;
 533 {
 534   if (! compute_change (&tz_rules[0], 1900 + tm->tm_year) ||
 535       ! compute_change (&tz_rules[1], 1900 + tm->tm_year))
 536     return 0;
 537
 538   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 539   __timezone = -tz_rules[0].offset;
 540   __tzname[0] = (char *) tz_rules[0].name;
 541   __tzname[1] = (char *) tz_rules[1].name;
 542
 543   {
 544     /* Keep __tzname_cur_max up to date.  */
 545     size_t len0 = strlen (__tzname[0]);
 546     size_t len1 = strlen (__tzname[1]);
 547     if (len0 > __tzname_cur_max)
 548       __tzname_cur_max = len0;
 549     if (len1 > __tzname_cur_max)
 550       __tzname_cur_max = len1;
 551   }
 552
 553   return 1;
 554 }
 555 \f
 556 /* Reinterpret the TZ environment variable and set `tzname'.  */
 557 #undef tzset
 558
 559 void
 560 __tzset (void)
 561 {
 562   __libc_lock_lock (tzset_lock);
 563
 564   tzset_internal (1);
 565
 566   if (!__use_tzfile)
 567     {
 568       /* Set `tzname'.  */
 569       __tzname[0] = (char *) tz_rules[0].name;
 570       __tzname[1] = (char *) tz_rules[1].name;
 571     }
 572
 573   __libc_lock_unlock (tzset_lock);
 574 }
 575 weak_alias (__tzset, tzset)
 576 \f
 577 /* Return the `struct tm' representation of *TIMER in the local timezone.
 578    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 579 struct tm *
 580 __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
 581 {
 582   long int leap_correction;
 583   int leap_extra_secs;
 584
 585   if (timer == NULL)
 586     {
 587       __set_errno (EINVAL);
 588       return NULL;
 589     }
 590
 591   __libc_lock_lock (tzset_lock);
 592
 593   /* Update internal database according to current TZ setting.
 594      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 595      This is a good idea since this allows at least a bit more parallelism.
 596      By analogy we apply the same rule to gmtime_r.  */
 597   tzset_internal (tp == &_tmbuf);
 598
 599   if (__use_tzfile)
 600     {
 601       if (! __tzfile_compute (*timer, use_localtime,
 602                               &leap_correction, &leap_extra_secs, tp))
 603         tp = NULL;
 604     }
 605   else
 606     {
 607       if (! (__offtime (timer, 0, tp) && tz_compute (*timer, tp)))
 608         tp = NULL;
 609       leap_correction = 0L;
 610       leap_extra_secs = 0;
 611     }
 612
 613   if (tp)
 614     {
 615       if (use_localtime)
 616         {
 617           if (!__use_tzfile)
 618             {
 619               int isdst = (*timer >= tz_rules[0].change
 620                            && *timer < tz_rules[1].change);
 621               tp->tm_isdst = isdst;
 622               tp->tm_zone = __tzname[isdst];
 623               tp->tm_gmtoff = tz_rules[isdst].offset;
 624             }
 625         }
 626       else
 627         {
 628           tp->tm_isdst = 0;
 629           tp->tm_zone = "GMT";
 630           tp->tm_gmtoff = 0L;
 631         }
 632
 633       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 634         tp->tm_sec += leap_extra_secs;
 635       else
 636         tp = NULL;
 637     }
 638
 639   __libc_lock_unlock (tzset_lock);
 640
 641   return tp;
 642 }