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