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 = strdupa (tz);
 211
 212   if (sscanf (tz, "%[^0-9,+-]", tzbuf) != 1 ||
 213       (l = strlen (tzbuf)) < 3)
 214     return;
 215
 216   tz_rules[0].name = __tzstring (tzbuf);
 217
 218   tz += l;
 219
 220   /* Figure out the standard offset from UTC.  */
 221   if (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz)))
 222     return;
 223
 224   if (*tz == '-' || *tz == '+')
 225     tz_rules[0].offset = *tz++ == '-' ? 1L : -1L;
 226   else
 227     tz_rules[0].offset = -1L;
 228   switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 229     {
 230     default:
 231       return;
 232     case 1:
 233       mm = 0;
 234     case 2:
 235       ss = 0;
 236     case 3:
 237       break;
 238     }
 239   tz_rules[0].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 240                          (min (hh, 23) * 60 * 60));
 241
 242   for (l = 0; l < 3; ++l)
 243     {
 244       while (isdigit(*tz))
 245         ++tz;
 246       if (l < 2 && *tz == ':')
 247         ++tz;
 248     }
 249
 250   /* Get the DST timezone name (if any).  */
 251   if (*tz != '\0')
 252     {
 253       char *n = tzbuf + strlen (tzbuf) + 1;
 254       if (sscanf (tz, "%[^0-9,+-]", n) != 1 ||
 255           (l = strlen (n)) < 3)
 256         goto done_names;        /* Punt on name, set up the offsets.  */
 257
 258       tz_rules[1].name = __tzstring (n);
 259
 260       tz += l;
 261
 262       /* Figure out the DST offset from GMT.  */
 263       if (*tz == '-' || *tz == '+')
 264         tz_rules[1].offset = *tz++ == '-' ? 1L : -1L;
 265       else
 266         tz_rules[1].offset = -1L;
 267
 268       switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 269         {
 270         default:
 271           /* Default to one hour later than standard time.  */
 272           tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 273           break;
 274
 275         case 1:
 276           mm = 0;
 277         case 2:
 278           ss = 0;
 279         case 3:
 280           tz_rules[1].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 281                                  (min (hh, 23) * (60 * 60)));
 282           break;
 283         }
 284       for (l = 0; l < 3; ++l)
 285         {
 286           while (isdigit (*tz))
 287             ++tz;
 288           if (l < 2 && *tz == ':')
 289             ++tz;
 290         }
 291       if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 292         {
 293           /* There is no rule.  See if there is a default rule file.  */
 294           __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 295                             tz_rules[0].offset, tz_rules[1].offset);
 296           if (__use_tzfile)
 297             {
 298               free (old_tz);
 299               old_tz = NULL;
 300               return;
 301             }
 302         }
 303     }
 304   else
 305     {
 306       /* There is no DST.  */
 307       tz_rules[1].name = tz_rules[0].name;
 308       tz_rules[1].offset = tz_rules[0].offset;
 309       goto out;
 310     }
 311
 312  done_names:
 313   /* Figure out the standard <-> DST rules.  */
 314   for (whichrule = 0; whichrule < 2; ++whichrule)
 315     {
 316       register tz_rule *tzr = &tz_rules[whichrule];
 317
 318       /* Ignore comma to support string following the incorrect
 319          specification in early POSIX.1 printings.  */
 320       tz += *tz == ',';
 321
 322       /* Get the date of the change.  */
 323       if (*tz == 'J' || isdigit (*tz))
 324         {
 325           char *end;
 326           tzr->type = *tz == 'J' ? J1 : J0;
 327           if (tzr->type == J1 && !isdigit (*++tz))
 328             goto out;
 329           tzr->d = (unsigned short int) strtoul (tz, &end, 10);
 330           if (end == tz || tzr->d > 365)
 331             goto out;
 332           else if (tzr->type == J1 && tzr->d == 0)
 333             goto out;
 334           tz = end;
 335         }
 336       else if (*tz == 'M')
 337         {
 338           int n;
 339           tzr->type = M;
 340           if (sscanf (tz, "M%hu.%hu.%hu%n",
 341                       &tzr->m, &tzr->n, &tzr->d, &n) != 3 ||
 342               tzr->m < 1 || tzr->m > 12 ||
 343               tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 344             goto out;
 345           tz += n;
 346         }
 347       else if (*tz == '\0')
 348         {
 349           /* United States Federal Law, the equivalent of "M4.1.0,M10.5.0".  */
 350           tzr->type = M;
 351           if (tzr == &tz_rules[0])
 352             {
 353               tzr->m = 4;
 354               tzr->n = 1;
 355               tzr->d = 0;
 356             }
 357           else
 358             {
 359               tzr->m = 10;
 360               tzr->n = 5;
 361               tzr->d = 0;
 362             }
 363         }
 364       else
 365         goto out;
 366
 367       if (*tz != '\0' && *tz != '/' && *tz != ',')
 368         goto out;
 369       else if (*tz == '/')
 370         {
 371           /* Get the time of day of the change.  */
 372           ++tz;
 373           if (*tz == '\0')
 374             goto out;
 375           switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 376             {
 377             default:
 378               hh = 2;           /* Default to 2:00 AM.  */
 379             case 1:
 380               mm = 0;
 381             case 2:
 382               ss = 0;
 383             case 3:
 384               break;
 385             }
 386           for (l = 0; l < 3; ++l)
 387             {
 388               while (isdigit (*tz))
 389                 ++tz;
 390               if (l < 2 && *tz == ':')
 391                 ++tz;
 392             }
 393           tzr->secs = (hh * 60 * 60) + (mm * 60) + ss;
 394         }
 395       else
 396         /* Default to 2:00 AM.  */
 397         tzr->secs = 2 * 60 * 60;
 398
 399       tzr->computed_for = -1;
 400     }
 401
 402  out:
 403   /* We know the offset now, set `__timezone'.  */
 404   __timezone = -tz_rules[0].offset;
 405 }
 406 \f
 407 /* Maximum length of a timezone name.  __tz_compute keeps this up to date
 408    (never decreasing it) when ! __use_tzfile.
 409    tzfile.c keeps it up to date when __use_tzfile.  */
 410 size_t __tzname_cur_max;
 411
 412 long int
 413 __tzname_max ()
 414 {
 415   __libc_lock_lock (tzset_lock);
 416
 417   tzset_internal (0);
 418
 419   __libc_lock_unlock (tzset_lock);
 420
 421   return __tzname_cur_max;
 422 }
 423 \f
 424 /* Figure out the exact time (as a time_t) in YEAR
 425    when the change described by RULE will occur and
 426    put it in RULE->change, saving YEAR in RULE->computed_for.
 427    Return nonzero if successful, zero on failure.  */
 428 static int
 429 internal_function
 430 compute_change (rule, year)
 431      tz_rule *rule;
 432      int year;
 433 {
 434   register time_t t;
 435   int y;
 436
 437   if (year != -1 && rule->computed_for == year)
 438     /* Operations on times in 1969 will be slower.  Oh well.  */
 439     return 1;
 440
 441   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 442   t = 0;
 443   for (y = 1970; y < year; ++y)
 444     t += SECSPERDAY * (__isleap (y) ? 366 : 365);
 445
 446   switch (rule->type)
 447     {
 448     case J1:
 449       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 450          In non-leap years, or if the day number is 59 or less, just
 451          add SECSPERDAY times the day number-1 to the time of
 452          January 1, midnight, to get the day.  */
 453       t += (rule->d - 1) * SECSPERDAY;
 454       if (rule->d >= 60 && __isleap (year))
 455         t += SECSPERDAY;
 456       break;
 457
 458     case J0:
 459       /* n - Day of year.
 460          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 461       t += rule->d * SECSPERDAY;
 462       break;
 463
 464     case M:
 465       /* Mm.n.d - Nth "Dth day" of month M.  */
 466       {
 467         unsigned int i;
 468         int d, m1, yy0, yy1, yy2, dow;
 469         const unsigned short int *myday =
 470           &__mon_yday[__isleap (year)][rule->m];
 471
 472         /* First add SECSPERDAY for each day in months before M.  */
 473         t += myday[-1] * SECSPERDAY;
 474
 475         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 476         m1 = (rule->m + 9) % 12 + 1;
 477         yy0 = (rule->m <= 2) ? (year - 1) : year;
 478         yy1 = yy0 / 100;
 479         yy2 = yy0 % 100;
 480         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 481         if (dow < 0)
 482           dow += 7;
 483
 484         /* DOW is the day-of-week of the first day of the month.  Get the
 485            day-of-month (zero-origin) of the first DOW day of the month.  */
 486         d = rule->d - dow;
 487         if (d < 0)
 488           d += 7;
 489         for (i = 1; i < rule->n; ++i)
 490           {
 491             if (d + 7 >= (int) myday[0] - myday[-1])
 492               break;
 493             d += 7;
 494           }
 495
 496         /* D is the day-of-month (zero-origin) of the day we want.  */
 497         t += d * SECSPERDAY;
 498       }
 499       break;
 500     }
 501
 502   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 503      Just add the time of day and local offset from GMT, and we're done.  */
 504
 505   rule->change = t - rule->offset + rule->secs;
 506   rule->computed_for = year;
 507   return 1;
 508 }
 509
 510
 511 /* Figure out the correct timezone for *TIMER and TM (which must be the same)
 512    and set `__tzname', `__timezone', and `__daylight' accordingly.
 513    Return nonzero on success, zero on failure.  */
 514 static int
 515 internal_function
 516 tz_compute (timer, tm)
 517      time_t timer;
 518      const struct tm *tm;
 519 {
 520   if (! compute_change (&tz_rules[0], 1900 + tm->tm_year) ||
 521       ! compute_change (&tz_rules[1], 1900 + tm->tm_year))
 522     return 0;
 523
 524   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 525   __timezone = -tz_rules[0].offset;
 526   __tzname[0] = (char *) tz_rules[0].name;
 527   __tzname[1] = (char *) tz_rules[1].name;
 528
 529   {
 530     /* Keep __tzname_cur_max up to date.  */
 531     size_t len0 = strlen (__tzname[0]);
 532     size_t len1 = strlen (__tzname[1]);
 533     if (len0 > __tzname_cur_max)
 534       __tzname_cur_max = len0;
 535     if (len1 > __tzname_cur_max)
 536       __tzname_cur_max = len1;
 537   }
 538
 539   return 1;
 540 }
 541 \f
 542 /* Reinterpret the TZ environment variable and set `tzname'.  */
 543 #undef tzset
 544
 545 void
 546 __tzset (void)
 547 {
 548   __libc_lock_lock (tzset_lock);
 549
 550   tzset_internal (1);
 551
 552   if (!__use_tzfile)
 553     {
 554       /* Set `tzname'.  */
 555       __tzname[0] = (char *) tz_rules[0].name;
 556       __tzname[1] = (char *) tz_rules[1].name;
 557     }
 558
 559   __libc_lock_unlock (tzset_lock);
 560 }
 561 weak_alias (__tzset, tzset)
 562 \f
 563 /* Return the `struct tm' representation of *TIMER in the local timezone.
 564    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 565 struct tm *
 566 __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
 567 {
 568   long int leap_correction;
 569   int leap_extra_secs;
 570
 571   if (timer == NULL)
 572     {
 573       __set_errno (EINVAL);
 574       return NULL;
 575     }
 576
 577   __libc_lock_lock (tzset_lock);
 578
 579   /* Update internal database according to current TZ setting.
 580      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 581      This is a good idea since this allows at least a bit more parallelism.
 582      By analogy we apply the same rule to gmtime_r.  */
 583   tzset_internal (tp == &_tmbuf);
 584
 585   if (__use_tzfile)
 586     {
 587       if (! __tzfile_compute (*timer, use_localtime,
 588                               &leap_correction, &leap_extra_secs, tp))
 589         tp = NULL;
 590     }
 591   else
 592     {
 593       if (! (__offtime (timer, 0, tp) && tz_compute (*timer, tp)))
 594         tp = NULL;
 595       leap_correction = 0L;
 596       leap_extra_secs = 0;
 597     }
 598
 599   if (tp)
 600     {
 601       if (use_localtime)
 602         {
 603           if (!__use_tzfile)
 604             {
 605               int isdst = (*timer >= tz_rules[0].change
 606                            && *timer < tz_rules[1].change);
 607               tp->tm_isdst = isdst;
 608               tp->tm_zone = __tzname[isdst];
 609               tp->tm_gmtoff = tz_rules[isdst].offset;
 610             }
 611         }
 612       else
 613         {
 614           tp->tm_isdst = 0;
 615           tp->tm_zone = "GMT";
 616           tp->tm_gmtoff = 0L;
 617         }
 618
 619       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 620         tp->tm_sec += leap_extra_secs;
 621       else
 622         tp = NULL;
 623     }
 624
 625   __libc_lock_unlock (tzset_lock);
 626
 627   return tp;
 628 }