time/tzset.c

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