time/tzset.c

   1 /* Copyright (C) 1991-2012 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <ctype.h>
  19 #include <errno.h>
  20 #include <bits/libc-lock.h>
  21 #include <stddef.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <time.h>
  26
  27
  28 #define NOID
  29 #include <timezone/tzfile.h>
  30
  31 char *__tzname[2] = { (char *) "GMT", (char *) "GMT" };
  32 int __daylight = 0;
  33 long int __timezone = 0L;
  34
  35 weak_alias (__tzname, tzname)
  36 weak_alias (__daylight, daylight)
  37 weak_alias (__timezone, timezone)
  38
  39 /* This locks all the state variables in tzfile.c and this file.  */
  40 __libc_lock_define_initialized (static, tzset_lock)
  41
  42
  43 #define min(a, b)       ((a) < (b) ? (a) : (b))
  44 #define max(a, b)       ((a) > (b) ? (a) : (b))
  45 #define sign(x)         ((x) < 0 ? -1 : 1)
  46
  47
  48 /* This structure contains all the information about a
  49    timezone given in the POSIX standard TZ envariable.  */
  50 typedef struct
  51   {
  52     const char *name;
  53
  54     /* When to change.  */
  55     enum { J0, J1, M } type;    /* Interpretation of:  */
  56     unsigned short int m, n, d; /* Month, week, day.  */
  57     unsigned int secs;          /* Time of day.  */
  58
  59     long int offset;            /* Seconds east of GMT (west if < 0).  */
  60
  61     /* We cache the computed time of change for a
  62        given year so we don't have to recompute it.  */
  63     time_t change;      /* When to change to this zone.  */
  64     int computed_for;   /* Year above is computed for.  */
  65   } tz_rule;
  66
  67 /* tz_rules[0] is standard, tz_rules[1] is daylight.  */
  68 static tz_rule tz_rules[2];
  69
  70
  71 static void compute_change (tz_rule *rule, int year) __THROW internal_function;
  72 static void tzset_internal (int always, int explicit)
  73      __THROW internal_function;
  74 \f
  75 /* List of buffers containing time zone strings. */
  76 struct tzstring_l
  77 {
  78   struct tzstring_l *next;
  79   size_t len;  /* strlen(data) - doesn't count terminating NUL! */
  80   char data[0];
  81 };
  82
  83 static struct tzstring_l *tzstring_list;
  84
  85 /* Allocate a permanent home for S.  It will never be moved or deallocated,
  86    but may share space with other strings.
  87    Don't modify the returned string. */
  88 char *
  89 __tzstring (const char *s)
  90 {
  91   char *p;
  92   struct tzstring_l *t, *u, *new;
  93   size_t len = strlen (s);
  94
  95   /* Walk the list and look for a match.  If this string is the same
  96      as the end of an already-allocated string, it can share space. */
  97   for (u = t = tzstring_list; t; u = t, t = t->next)
  98     if (len <= t->len)
  99       {
 100         p = &t->data[t->len - len];
 101         if (strcmp (s, p) == 0)
 102           return p;
 103       }
 104
 105   /* Not found; allocate a new buffer. */
 106   new = malloc (sizeof (struct tzstring_l) + len + 1);
 107   if (!new)
 108     return NULL;
 109
 110   new->next = NULL;
 111   new->len = len;
 112   strcpy (new->data, s);
 113
 114   if (u)
 115     u->next = new;
 116   else
 117     tzstring_list = new;
 118
 119   return new->data;
 120 }
 121 \f
 122 /* Maximum length of a timezone name.  tzset_internal keeps this up to date
 123    (never decreasing it) when ! __use_tzfile.
 124    tzfile.c keeps it up to date when __use_tzfile.  */
 125 size_t __tzname_cur_max;
 126
 127 long int
 128 __tzname_max ()
 129 {
 130   __libc_lock_lock (tzset_lock);
 131
 132   tzset_internal (0, 0);
 133
 134   __libc_lock_unlock (tzset_lock);
 135
 136   return __tzname_cur_max;
 137 }
 138 \f
 139 static char *old_tz;
 140
 141 static void
 142 internal_function
 143 update_vars (void)
 144 {
 145   __daylight = tz_rules[0].offset != tz_rules[1].offset;
 146   __timezone = -tz_rules[0].offset;
 147   __tzname[0] = (char *) tz_rules[0].name;
 148   __tzname[1] = (char *) tz_rules[1].name;
 149
 150   /* Keep __tzname_cur_max up to date.  */
 151   size_t len0 = strlen (__tzname[0]);
 152   size_t len1 = strlen (__tzname[1]);
 153   if (len0 > __tzname_cur_max)
 154     __tzname_cur_max = len0;
 155   if (len1 > __tzname_cur_max)
 156     __tzname_cur_max = len1;
 157 }
 158
 159
 160 static unsigned int
 161 __attribute_noinline__
 162 compute_offset (unsigned int ss, unsigned int mm, unsigned int hh)
 163 {
 164   return min (ss, 59) + min (mm, 59) * 60 + min (hh, 24) * 60 * 60;
 165 }
 166
 167
 168 /* Parse the POSIX TZ-style string.  */
 169 void
 170 __tzset_parse_tz (tz)
 171      const char *tz;
 172 {
 173   unsigned short int hh, mm, ss;
 174
 175   /* Clear out old state and reset to unnamed UTC.  */
 176   memset (tz_rules, '\0', sizeof tz_rules);
 177   tz_rules[0].name = tz_rules[1].name = "";
 178
 179   /* Get the standard timezone name.  */
 180   char *tzbuf = strdupa (tz);
 181
 182   int consumed;
 183   if (sscanf (tz, "%[A-Za-z]%n", tzbuf, &consumed) != 1)
 184     {
 185       /* Check for the quoted version.  */
 186       char *wp = tzbuf;
 187       if (__builtin_expect (*tz++ != '<', 0))
 188         goto out;
 189
 190       while (isalnum (*tz) || *tz == '+' || *tz == '-')
 191         *wp++ = *tz++;
 192       if (__builtin_expect (*tz++ != '>' || wp - tzbuf < 3, 0))
 193         goto out;
 194       *wp = '\0';
 195     }
 196   else if (__builtin_expect (consumed < 3, 0))
 197     goto out;
 198   else
 199     tz += consumed;
 200
 201   tz_rules[0].name = __tzstring (tzbuf);
 202
 203   /* Figure out the standard offset from UTC.  */
 204   if (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz)))
 205     goto out;
 206
 207   if (*tz == '-' || *tz == '+')
 208     tz_rules[0].offset = *tz++ == '-' ? 1L : -1L;
 209   else
 210     tz_rules[0].offset = -1L;
 211   switch (sscanf (tz, "%hu%n:%hu%n:%hu%n",
 212                   &hh, &consumed, &mm, &consumed, &ss, &consumed))
 213     {
 214     default:
 215       tz_rules[0].offset = 0;
 216       goto out;
 217     case 1:
 218       mm = 0;
 219     case 2:
 220       ss = 0;
 221     case 3:
 222       break;
 223     }
 224   tz_rules[0].offset *= compute_offset (ss, mm, hh);
 225   tz += consumed;
 226
 227   /* Get the DST timezone name (if any).  */
 228   if (*tz != '\0')
 229     {
 230       if (sscanf (tz, "%[A-Za-z]%n", tzbuf, &consumed) != 1)
 231         {
 232           /* Check for the quoted version.  */
 233           char *wp = tzbuf;
 234           const char *rp = tz;
 235           if (__builtin_expect (*rp++ != '<', 0))
 236             /* Punt on name, set up the offsets.  */
 237             goto done_names;
 238
 239           while (isalnum (*rp) || *rp == '+' || *rp == '-')
 240             *wp++ = *rp++;
 241           if (__builtin_expect (*rp++ != '>' || wp - tzbuf < 3, 0))
 242             /* Punt on name, set up the offsets.  */
 243             goto done_names;
 244           *wp = '\0';
 245           tz = rp;
 246         }
 247       else if (__builtin_expect (consumed < 3, 0))
 248         /* Punt on name, set up the offsets.  */
 249         goto done_names;
 250       else
 251         tz += consumed;
 252
 253       tz_rules[1].name = __tzstring (tzbuf);
 254
 255       /* Figure out the DST offset from GMT.  */
 256       if (*tz == '-' || *tz == '+')
 257         tz_rules[1].offset = *tz++ == '-' ? 1L : -1L;
 258       else
 259         tz_rules[1].offset = -1L;
 260
 261       switch (sscanf (tz, "%hu%n:%hu%n:%hu%n",
 262                       &hh, &consumed, &mm, &consumed, &ss, &consumed))
 263         {
 264         default:
 265           /* Default to one hour later than standard time.  */
 266           tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 267           break;
 268
 269         case 1:
 270           mm = 0;
 271         case 2:
 272           ss = 0;
 273         case 3:
 274           tz_rules[1].offset *= compute_offset (ss, mm, hh);
 275           tz += consumed;
 276           break;
 277         }
 278       if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 279         {
 280           /* There is no rule.  See if there is a default rule file.  */
 281           __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 282                             tz_rules[0].offset, tz_rules[1].offset);
 283           if (__use_tzfile)
 284             {
 285               free (old_tz);
 286               old_tz = NULL;
 287               return;
 288             }
 289         }
 290     }
 291   else
 292     {
 293       /* There is no DST.  */
 294       tz_rules[1].name = tz_rules[0].name;
 295       tz_rules[1].offset = tz_rules[0].offset;
 296       goto out;
 297     }
 298
 299  done_names:
 300   /* Figure out the standard <-> DST rules.  */
 301   for (unsigned int whichrule = 0; whichrule < 2; ++whichrule)
 302     {
 303       register tz_rule *tzr = &tz_rules[whichrule];
 304
 305       /* Ignore comma to support string following the incorrect
 306          specification in early POSIX.1 printings.  */
 307       tz += *tz == ',';
 308
 309       /* Get the date of the change.  */
 310       if (*tz == 'J' || isdigit (*tz))
 311         {
 312           char *end;
 313           tzr->type = *tz == 'J' ? J1 : J0;
 314           if (tzr->type == J1 && !isdigit (*++tz))
 315             goto out;
 316           unsigned long int d = strtoul (tz, &end, 10);
 317           if (end == tz || d > 365)
 318             goto out;
 319           if (tzr->type == J1 && d == 0)
 320             goto out;
 321           tzr->d = d;
 322           tz = end;
 323         }
 324       else if (*tz == 'M')
 325         {
 326           tzr->type = M;
 327           if (sscanf (tz, "M%hu.%hu.%hu%n",
 328                       &tzr->m, &tzr->n, &tzr->d, &consumed) != 3
 329               || tzr->m < 1 || tzr->m > 12
 330               || tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 331             goto out;
 332           tz += consumed;
 333         }
 334       else if (*tz == '\0')
 335         {
 336          /* Daylight time rules in the U.S. are defined in the
 337             U.S. Code, Title 15, Chapter 6, Subchapter IX - Standard
 338             Time.  These dates were established by Congress in the
 339             Energy Policy Act of 2005 [Pub. L. no. 109-58, 119 Stat 594
 340             (2005)].
 341             Below is the equivalent of "M3.2.0,M11.1.0" [/2 not needed
 342             since 2:00AM is the default].  */
 343           tzr->type = M;
 344           if (tzr == &tz_rules[0])
 345             {
 346               tzr->m = 3;
 347               tzr->n = 2;
 348               tzr->d = 0;
 349             }
 350           else
 351             {
 352               tzr->m = 11;
 353               tzr->n = 1;
 354               tzr->d = 0;
 355             }
 356         }
 357       else
 358         goto out;
 359
 360       if (*tz != '\0' && *tz != '/' && *tz != ',')
 361         goto out;
 362       else if (*tz == '/')
 363         {
 364           /* Get the time of day of the change.  */
 365           ++tz;
 366           if (*tz == '\0')
 367             goto out;
 368           consumed = 0;
 369           switch (sscanf (tz, "%hu%n:%hu%n:%hu%n",
 370                           &hh, &consumed, &mm, &consumed, &ss, &consumed))
 371             {
 372             default:
 373               hh = 2;           /* Default to 2:00 AM.  */
 374             case 1:
 375               mm = 0;
 376             case 2:
 377               ss = 0;
 378             case 3:
 379               break;
 380             }
 381           tz += consumed;
 382           tzr->secs = (hh * 60 * 60) + (mm * 60) + ss;
 383         }
 384       else
 385         /* Default to 2:00 AM.  */
 386         tzr->secs = 2 * 60 * 60;
 387
 388       tzr->computed_for = -1;
 389     }
 390
 391  out:
 392   update_vars ();
 393 }
 394
 395 /* Interpret the TZ envariable.  */
 396 static void
 397 internal_function
 398 tzset_internal (always, explicit)
 399      int always;
 400      int explicit;
 401 {
 402   static int is_initialized;
 403   register const char *tz;
 404
 405   if (is_initialized && !always)
 406     return;
 407   is_initialized = 1;
 408
 409   /* Examine the TZ environment variable.  */
 410   tz = getenv ("TZ");
 411   if (tz == NULL && !explicit)
 412     /* Use the site-wide default.  This is a file name which means we
 413        would not see changes to the file if we compare only the file
 414        name for change.  We want to notice file changes if tzset() has
 415        been called explicitly.  Leave TZ as NULL in this case.  */
 416     tz = TZDEFAULT;
 417   if (tz && *tz == '\0')
 418     /* User specified the empty string; use UTC explicitly.  */
 419     tz = "Universal";
 420
 421   /* A leading colon means "implementation defined syntax".
 422      We ignore the colon and always use the same algorithm:
 423      try a data file, and if none exists parse the 1003.1 syntax.  */
 424   if (tz && *tz == ':')
 425     ++tz;
 426
 427   /* Check whether the value changed since the last run.  */
 428   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 429     /* No change, simply return.  */
 430     return;
 431
 432   if (tz == NULL)
 433     /* No user specification; use the site-wide default.  */
 434     tz = TZDEFAULT;
 435
 436   tz_rules[0].name = NULL;
 437   tz_rules[1].name = NULL;
 438
 439   /* Save the value of `tz'.  */
 440   free (old_tz);
 441   old_tz = tz ? __strdup (tz) : NULL;
 442
 443   /* Try to read a data file.  */
 444   __tzfile_read (tz, 0, NULL);
 445   if (__use_tzfile)
 446     return;
 447
 448   /* No data file found.  Default to UTC if nothing specified.  */
 449
 450   if (tz == NULL || *tz == '\0'
 451       || (TZDEFAULT != NULL && strcmp (tz, TZDEFAULT) == 0))
 452     {
 453       memset (tz_rules, '\0', sizeof tz_rules);
 454       tz_rules[0].name = tz_rules[1].name = "UTC";
 455       if (J0 != 0)
 456         tz_rules[0].type = tz_rules[1].type = J0;
 457       tz_rules[0].change = tz_rules[1].change = (time_t) -1;
 458       update_vars ();
 459       return;
 460     }
 461
 462   __tzset_parse_tz (tz);
 463 }
 464 \f
 465 /* Figure out the exact time (as a time_t) in YEAR
 466    when the change described by RULE will occur and
 467    put it in RULE->change, saving YEAR in RULE->computed_for.  */
 468 static void
 469 internal_function
 470 compute_change (rule, year)
 471      tz_rule *rule;
 472      int year;
 473 {
 474   register time_t t;
 475
 476   if (year != -1 && rule->computed_for == year)
 477     /* Operations on times in 2 BC will be slower.  Oh well.  */
 478     return;
 479
 480   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 481   if (year > 1970)
 482     t = ((year - 1970) * 365
 483          + /* Compute the number of leapdays between 1970 and YEAR
 484               (exclusive).  There is a leapday every 4th year ...  */
 485          + ((year - 1) / 4 - 1970 / 4)
 486          /* ... except every 100th year ... */
 487          - ((year - 1) / 100 - 1970 / 100)
 488          /* ... but still every 400th year.  */
 489          + ((year - 1) / 400 - 1970 / 400)) * SECSPERDAY;
 490   else
 491     t = 0;
 492
 493   switch (rule->type)
 494     {
 495     case J1:
 496       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 497          In non-leap years, or if the day number is 59 or less, just
 498          add SECSPERDAY times the day number-1 to the time of
 499          January 1, midnight, to get the day.  */
 500       t += (rule->d - 1) * SECSPERDAY;
 501       if (rule->d >= 60 && __isleap (year))
 502         t += SECSPERDAY;
 503       break;
 504
 505     case J0:
 506       /* n - Day of year.
 507          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 508       t += rule->d * SECSPERDAY;
 509       break;
 510
 511     case M:
 512       /* Mm.n.d - Nth "Dth day" of month M.  */
 513       {
 514         unsigned int i;
 515         int d, m1, yy0, yy1, yy2, dow;
 516         const unsigned short int *myday =
 517           &__mon_yday[__isleap (year)][rule->m];
 518
 519         /* First add SECSPERDAY for each day in months before M.  */
 520         t += myday[-1] * SECSPERDAY;
 521
 522         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 523         m1 = (rule->m + 9) % 12 + 1;
 524         yy0 = (rule->m <= 2) ? (year - 1) : year;
 525         yy1 = yy0 / 100;
 526         yy2 = yy0 % 100;
 527         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 528         if (dow < 0)
 529           dow += 7;
 530
 531         /* DOW is the day-of-week of the first day of the month.  Get the
 532            day-of-month (zero-origin) of the first DOW day of the month.  */
 533         d = rule->d - dow;
 534         if (d < 0)
 535           d += 7;
 536         for (i = 1; i < rule->n; ++i)
 537           {
 538             if (d + 7 >= (int) myday[0] - myday[-1])
 539               break;
 540             d += 7;
 541           }
 542
 543         /* D is the day-of-month (zero-origin) of the day we want.  */
 544         t += d * SECSPERDAY;
 545       }
 546       break;
 547     }
 548
 549   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 550      Just add the time of day and local offset from GMT, and we're done.  */
 551
 552   rule->change = t - rule->offset + rule->secs;
 553   rule->computed_for = year;
 554 }
 555
 556
 557 /* Figure out the correct timezone for TM and set `__tzname',
 558    `__timezone', and `__daylight' accordingly.  */
 559 void
 560 internal_function
 561 __tz_compute (timer, tm, use_localtime)
 562      time_t timer;
 563      struct tm *tm;
 564      int use_localtime;
 565 {
 566   compute_change (&tz_rules[0], 1900 + tm->tm_year);
 567   compute_change (&tz_rules[1], 1900 + tm->tm_year);
 568
 569   if (use_localtime)
 570     {
 571       int isdst;
 572
 573       /* We have to distinguish between northern and southern
 574          hemisphere.  For the latter the daylight saving time
 575          ends in the next year.  */
 576       if (__builtin_expect (tz_rules[0].change
 577                             > tz_rules[1].change, 0))
 578         isdst = (timer < tz_rules[1].change
 579                  || timer >= tz_rules[0].change);
 580       else
 581         isdst = (timer >= tz_rules[0].change
 582                  && timer < tz_rules[1].change);
 583       tm->tm_isdst = isdst;
 584       tm->tm_zone = __tzname[isdst];
 585       tm->tm_gmtoff = tz_rules[isdst].offset;
 586     }
 587 }
 588 \f
 589 /* Reinterpret the TZ environment variable and set `tzname'.  */
 590 #undef tzset
 591
 592 void
 593 __tzset (void)
 594 {
 595   __libc_lock_lock (tzset_lock);
 596
 597   tzset_internal (1, 1);
 598
 599   if (!__use_tzfile)
 600     {
 601       /* Set `tzname'.  */
 602       __tzname[0] = (char *) tz_rules[0].name;
 603       __tzname[1] = (char *) tz_rules[1].name;
 604     }
 605
 606   __libc_lock_unlock (tzset_lock);
 607 }
 608 weak_alias (__tzset, tzset)
 609 \f
 610 /* Return the `struct tm' representation of *TIMER in the local timezone.
 611    Use local time if USE_LOCALTIME is nonzero, UTC otherwise.  */
 612 struct tm *
 613 __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
 614 {
 615   long int leap_correction;
 616   int leap_extra_secs;
 617
 618   if (timer == NULL)
 619     {
 620       __set_errno (EINVAL);
 621       return NULL;
 622     }
 623
 624   __libc_lock_lock (tzset_lock);
 625
 626   /* Update internal database according to current TZ setting.
 627      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
 628      This is a good idea since this allows at least a bit more parallelism.  */
 629   tzset_internal (tp == &_tmbuf && use_localtime, 1);
 630
 631   if (__use_tzfile)
 632     __tzfile_compute (*timer, use_localtime, &leap_correction,
 633                       &leap_extra_secs, tp);
 634   else
 635     {
 636       if (! __offtime (timer, 0, tp))
 637         tp = NULL;
 638       else
 639         __tz_compute (*timer, tp, use_localtime);
 640       leap_correction = 0L;
 641       leap_extra_secs = 0;
 642     }
 643
 644   if (tp)
 645     {
 646       if (! use_localtime)
 647         {
 648           tp->tm_isdst = 0;
 649           tp->tm_zone = "GMT";
 650           tp->tm_gmtoff = 0L;
 651         }
 652
 653       if (__offtime (timer, tp->tm_gmtoff - leap_correction, tp))
 654         tp->tm_sec += leap_extra_secs;
 655       else
 656         tp = NULL;
 657     }
 658
 659   __libc_lock_unlock (tzset_lock);
 660
 661   return tp;
 662 }
 663
 664
 665 libc_freeres_fn (free_mem)
 666 {
 667   while (tzstring_list != NULL)
 668     {
 669       struct tzstring_l *old = tzstring_list;
 670
 671       tzstring_list = tzstring_list->next;
 672       free (old);
 673     }
 674   free (old_tz);
 675   old_tz = NULL;
 676 }