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 <stddef.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <time.h>
  25
  26 /* Defined in mktime.c.  */
  27 extern const unsigned short int __mon_yday[2][13];
  28
  29 #define NOID
  30 #include "tzfile.h"
  31
  32 extern int __use_tzfile;
  33 extern void __tzfile_read __P ((const char *file));
  34 extern void __tzfile_default __P ((char *std, char *dst,
  35                                    long int stdoff, long int dstoff));
  36 extern int __tz_compute __P ((time_t timer, const struct tm *tm));
  37
  38 char *__tzname[2] = { (char *) "GMT", (char *) "GMT" };
  39 int __daylight = 0;
  40 long int __timezone = 0L;
  41
  42 weak_alias (__tzname, tzname)
  43 weak_alias (__daylight, daylight)
  44 weak_alias (__timezone, timezone)
  45
  46
  47 #define min(a, b)       ((a) < (b) ? (a) : (b))
  48 #define max(a, b)       ((a) > (b) ? (a) : (b))
  49 #define sign(x)         ((x) < 0 ? -1 : 1)
  50
  51
  52 /* This structure contains all the information about a
  53    timezone given in the POSIX standard TZ envariable.  */
  54 typedef struct
  55   {
  56     char *name;
  57
  58     /* When to change.  */
  59     enum { J0, J1, M } type;    /* Interpretation of:  */
  60     unsigned short int m, n, d; /* Month, week, day.  */
  61     unsigned int secs;          /* Time of day.  */
  62
  63     long int offset;            /* Seconds east of GMT (west if < 0).  */
  64
  65     /* We cache the computed time of change for a
  66        given year so we don't have to recompute it.  */
  67     time_t change;      /* When to change to this zone.  */
  68     int computed_for;   /* Year above is computed for.  */
  69   } tz_rule;
  70
  71 /* tz_rules[0] is standard, tz_rules[1] is daylight.  */
  72 static tz_rule tz_rules[2];
  73
  74
  75 static int compute_change __P ((tz_rule *rule, int year));
  76 \f
  77 static char *old_tz = NULL;
  78
  79 /* Interpret the TZ envariable.  */
  80 void __tzset_internal __P ((int always));
  81 void
  82 __tzset_internal (always)
  83      int always;
  84 {
  85   static int is_initialized = 0;
  86   register const char *tz;
  87   register size_t l;
  88   unsigned short int hh, mm, ss;
  89   unsigned short int whichrule;
  90
  91   if (is_initialized && !always)
  92     return;
  93   is_initialized = 1;
  94
  95   /* Examine the TZ environment variable.  */
  96   tz = getenv ("TZ");
  97   if (tz == NULL)
  98     /* No user specification; use the site-wide default.  */
  99     tz = TZDEFAULT;
 100   else if (*tz == '\0')
 101     /* User specified the empty string; use UTC explicitly.  */
 102     tz = "Universal";
 103
 104   /* A leading colon means "implementation defined syntax".
 105      We ignore the colon and always use the same algorithm:
 106      try a data file, and if none exists parse the 1003.1 syntax.  */
 107   if (tz && *tz == ':')
 108     ++tz;
 109
 110   /* Check whether the value changes since the last run.  */
 111   if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
 112     /* No change, simply return.  */
 113     return;
 114
 115   /* Free old storage.  */
 116   if (tz_rules[0].name != NULL && *tz_rules[0].name != '\0')
 117     free ((void *) tz_rules[0].name);
 118   if (tz_rules[1].name != NULL && *tz_rules[1].name != '\0' &&
 119       tz_rules[1].name != tz_rules[0].name)
 120     free ((void *) tz_rules[1].name);
 121   tz_rules[0].name = NULL;
 122   tz_rules[1].name = NULL;
 123
 124   /* Save the value of `tz'.  */
 125   if (old_tz != NULL)
 126     free (old_tz);
 127   old_tz = tz ? __strdup (tz) : NULL;
 128
 129   /* Try to read a data file.  */
 130   __tzfile_read (tz);
 131   if (__use_tzfile)
 132     return;
 133
 134   /* No data file found.  Default to UTC if nothing specified.  */
 135
 136   if (tz == NULL || *tz == '\0')
 137     {
 138       static const char UTC[] = "UTC";
 139       size_t len = sizeof UTC;
 140       tz_rules[0].name = (char *) malloc (len);
 141       if (tz_rules[0].name == NULL)
 142         return;
 143       tz_rules[1].name = (char *) malloc (len);
 144       if (tz_rules[1].name == NULL)
 145         return;
 146       memcpy ((void *) tz_rules[0].name, UTC, len);
 147       memcpy ((void *) tz_rules[1].name, UTC, len);
 148       tz_rules[0].type = tz_rules[1].type = J0;
 149       tz_rules[0].m = tz_rules[0].n = tz_rules[0].d = 0;
 150       tz_rules[1].m = tz_rules[1].n = tz_rules[1].d = 0;
 151       tz_rules[0].secs = tz_rules[1].secs = 0;
 152       tz_rules[0].offset = tz_rules[1].offset = 0L;
 153       tz_rules[0].change = tz_rules[1].change = (time_t) -1;
 154       tz_rules[0].computed_for = tz_rules[1].computed_for = 0;
 155       return;
 156     }
 157
 158   /* Clear out old state and reset to unnamed UTC.  */
 159   memset (tz_rules, 0, sizeof tz_rules);
 160   tz_rules[0].name = tz_rules[1].name = (char *) "";
 161
 162   /* Get the standard timezone name.  */
 163   tz_rules[0].name = (char *) malloc (strlen (tz) + 1);
 164   if (tz_rules[0].name == NULL)
 165     {
 166       /* Clear the old tz name so we will try again.  */
 167       free (old_tz);
 168       old_tz = NULL;
 169       return;
 170     }
 171
 172   if (sscanf (tz, "%[^0-9,+-]", tz_rules[0].name) != 1 ||
 173       (l = strlen(tz_rules[0].name)) < 3)
 174     {
 175       free (tz_rules[0].name);
 176       tz_rules[0].name = (char *) "";
 177       return;
 178     }
 179
 180   {
 181     char *n = realloc ((void *) tz_rules[0].name, l + 1);
 182     if (n != NULL)
 183       tz_rules[0].name = n;
 184   }
 185
 186   tz += l;
 187
 188   /* Figure out the standard offset from UTC.  */
 189   if (*tz == '\0' || (*tz != '+' && *tz != '-' && !isdigit (*tz)))
 190     return;
 191
 192   if (*tz == '-' || *tz == '+')
 193     tz_rules[0].offset = *tz++ == '-' ? 1L : -1L;
 194   else
 195     tz_rules[0].offset = -1L;
 196   switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 197     {
 198     default:
 199       return;
 200     case 1:
 201       mm = 0;
 202     case 2:
 203       ss = 0;
 204     case 3:
 205       break;
 206     }
 207   tz_rules[0].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 208                          (min (hh, 23) * 60 * 60));
 209
 210   for (l = 0; l < 3; ++l)
 211     {
 212       while (isdigit(*tz))
 213         ++tz;
 214       if (l < 2 && *tz == ':')
 215         ++tz;
 216     }
 217
 218   /* Get the DST timezone name (if any).  */
 219   if (*tz != '\0')
 220     {
 221       char *n = malloc (strlen (tz) + 1);
 222       if (n != NULL)
 223         {
 224           tz_rules[1].name = n;
 225           if (sscanf (tz, "%[^0-9,+-]", tz_rules[1].name) != 1 ||
 226               (l = strlen (tz_rules[1].name)) < 3)
 227             {
 228               free (n);
 229               tz_rules[1].name = (char *) "";
 230               goto done_names;  /* Punt on name, set up the offsets.  */
 231             }
 232           n = realloc ((void *) tz_rules[1].name, l + 1);
 233           if (n != NULL)
 234             tz_rules[1].name = n;
 235
 236           tz += l;
 237         }
 238
 239       /* Figure out the DST offset from GMT.  */
 240       if (*tz == '-' || *tz == '+')
 241         tz_rules[1].offset = *tz++ == '-' ? 1L : -1L;
 242       else
 243         tz_rules[1].offset = -1L;
 244
 245       switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 246         {
 247         default:
 248           /* Default to one hour later than standard time.  */
 249           tz_rules[1].offset = tz_rules[0].offset + (60 * 60);
 250           break;
 251
 252         case 1:
 253           mm = 0;
 254         case 2:
 255           ss = 0;
 256         case 3:
 257           tz_rules[1].offset *= (min (ss, 59) + (min (mm, 59) * 60) +
 258                                  (min (hh, 23) * (60 * 60)));
 259           break;
 260         }
 261       for (l = 0; l < 3; ++l)
 262         {
 263           while (isdigit (*tz))
 264             ++tz;
 265           if (l < 2 && *tz == ':')
 266             ++tz;
 267         }
 268     }
 269   else
 270     /* There is no DST.  */
 271     tz_rules[1].name = tz_rules[0].name;
 272
 273  done_names:
 274
 275   if (*tz == '\0' || (tz[0] == ',' && tz[1] == '\0'))
 276     {
 277       /* There is no rule.  See if there is a default rule file.  */
 278       __tzfile_default (tz_rules[0].name, tz_rules[1].name,
 279                         tz_rules[0].offset, tz_rules[1].offset);
 280       if (__use_tzfile)
 281         {
 282           free (old_tz);
 283           old_tz = NULL;
 284           return;
 285         }
 286     }
 287
 288   /* Figure out the standard <-> DST rules.  */
 289   for (whichrule = 0; whichrule < 2; ++whichrule)
 290     {
 291       register tz_rule *tzr = &tz_rules[whichrule];
 292
 293       if (*tz == ',')
 294         {
 295           ++tz;
 296           if (*tz == '\0')
 297             return;
 298         }
 299
 300       /* Get the date of the change.  */
 301       if (*tz == 'J' || isdigit (*tz))
 302         {
 303           char *end;
 304           tzr->type = *tz == 'J' ? J1 : J0;
 305           if (tzr->type == J1 && !isdigit (*++tz))
 306             return;
 307           tzr->d = (unsigned short int) strtoul (tz, &end, 10);
 308           if (end == tz || tzr->d > 365)
 309             return;
 310           else if (tzr->type == J1 && tzr->d == 0)
 311             return;
 312           tz = end;
 313         }
 314       else if (*tz == 'M')
 315         {
 316           int n;
 317           tzr->type = M;
 318           if (sscanf (tz, "M%hu.%hu.%hu%n",
 319                       &tzr->m, &tzr->n, &tzr->d, &n) != 3 ||
 320               tzr->m < 1 || tzr->m > 12 ||
 321               tzr->n < 1 || tzr->n > 5 || tzr->d > 6)
 322             return;
 323           tz += n;
 324         }
 325       else if (*tz == '\0')
 326         {
 327           /* United States Federal Law, the equivalent of "M4.1.0,M10.5.0".  */
 328           tzr->type = M;
 329           if (tzr == &tz_rules[0])
 330             {
 331               tzr->m = 4;
 332               tzr->n = 1;
 333               tzr->d = 0;
 334             }
 335           else
 336             {
 337               tzr->m = 10;
 338               tzr->n = 5;
 339               tzr->d = 0;
 340             }
 341         }
 342       else
 343         return;
 344
 345       if (*tz != '\0' && *tz != '/' && *tz != ',')
 346         return;
 347       else if (*tz == '/')
 348         {
 349           /* Get the time of day of the change.  */
 350           ++tz;
 351           if (*tz == '\0')
 352             return;
 353           switch (sscanf (tz, "%hu:%hu:%hu", &hh, &mm, &ss))
 354             {
 355             default:
 356               hh = 2;           /* Default to 2:00 AM.  */
 357             case 1:
 358               mm = 0;
 359             case 2:
 360               ss = 0;
 361             case 3:
 362               break;
 363             }
 364           for (l = 0; l < 3; ++l)
 365             {
 366               while (isdigit (*tz))
 367                 ++tz;
 368               if (l < 2 && *tz == ':')
 369                 ++tz;
 370             }
 371           tzr->secs = (hh * 60 * 60) + (mm * 60) + ss;
 372         }
 373       else
 374         /* Default to 2:00 AM.  */
 375         tzr->secs = 2 * 60 * 60;
 376
 377       tzr->computed_for = -1;
 378     }
 379 }
 380 \f
 381 /* Maximum length of a timezone name.  __tz_compute keeps this up to date
 382    (never decreasing it) when ! __use_tzfile.
 383    tzfile.c keeps it up to date when __use_tzfile.  */
 384 size_t __tzname_cur_max;
 385
 386 long int
 387 __tzname_max ()
 388 {
 389   __tzset_internal (0);
 390
 391   return __tzname_cur_max;
 392 }
 393 \f
 394 /* Figure out the exact time (as a time_t) in YEAR
 395    when the change described by RULE will occur and
 396    put it in RULE->change, saving YEAR in RULE->computed_for.
 397    Return nonzero if successful, zero on failure.  */
 398 static int
 399 compute_change (rule, year)
 400      tz_rule *rule;
 401      int year;
 402 {
 403   register time_t t;
 404   int y;
 405
 406   if (year != -1 && rule->computed_for == year)
 407     /* Operations on times in 1969 will be slower.  Oh well.  */
 408     return 1;
 409
 410   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
 411   t = 0;
 412   for (y = 1970; y < year; ++y)
 413     t += SECSPERDAY * (__isleap (y) ? 366 : 365);
 414
 415   switch (rule->type)
 416     {
 417     case J1:
 418       /* Jn - Julian day, 1 == January 1, 60 == March 1 even in leap years.
 419          In non-leap years, or if the day number is 59 or less, just
 420          add SECSPERDAY times the day number-1 to the time of
 421          January 1, midnight, to get the day.  */
 422       t += (rule->d - 1) * SECSPERDAY;
 423       if (rule->d >= 60 && __isleap (year))
 424         t += SECSPERDAY;
 425       break;
 426
 427     case J0:
 428       /* n - Day of year.
 429          Just add SECSPERDAY times the day number to the time of Jan 1st.  */
 430       t += rule->d * SECSPERDAY;
 431       break;
 432
 433     case M:
 434       /* Mm.n.d - Nth "Dth day" of month M.  */
 435       {
 436         register int i, d, m1, yy0, yy1, yy2, dow;
 437         register const unsigned short int *myday =
 438           &__mon_yday[__isleap (year)][rule->m];
 439
 440         /* First add SECSPERDAY for each day in months before M.  */
 441         t += myday[-1] * SECSPERDAY;
 442
 443         /* Use Zeller's Congruence to get day-of-week of first day of month. */
 444         m1 = (rule->m + 9) % 12 + 1;
 445         yy0 = (rule->m <= 2) ? (year - 1) : year;
 446         yy1 = yy0 / 100;
 447         yy2 = yy0 % 100;
 448         dow = ((26 * m1 - 2) / 10 + 1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
 449         if (dow < 0)
 450           dow += 7;
 451
 452         /* DOW is the day-of-week of the first day of the month.  Get the
 453            day-of-month (zero-origin) of the first DOW day of the month.  */
 454         d = rule->d - dow;
 455         if (d < 0)
 456           d += 7;
 457         for (i = 1; i < rule->n; ++i)
 458           {
 459             if (d + 7 >= myday[0] - myday[-1])
 460               break;
 461             d += 7;
 462           }
 463
 464         /* D is the day-of-month (zero-origin) of the day we want.  */
 465         t += d * SECSPERDAY;
 466       }
 467       break;
 468     }
 469
 470   /* T is now the Epoch-relative time of 0:00:00 GMT on the day we want.
 471      Just add the time of day and local offset from GMT, and we're done.  */
 472
 473   rule->change = t - rule->offset + rule->secs;
 474   rule->computed_for = year;
 475   return 1;
 476 }
 477
 478
 479 /* Figure out the correct timezone for *TIMER and TM (which must be the same)
 480    and set `__tzname', `__timezone', and `__daylight' accordingly.
 481    Return nonzero on success, zero on failure.  */
 482 int
 483 __tz_compute (timer, tm)
 484      time_t timer;
 485      const struct tm *tm;
 486 {
 487   __tzset_internal (0);
 488
 489   if (! compute_change (&tz_rules[0], 1900 + tm->tm_year) ||
 490       ! compute_change (&tz_rules[1], 1900 + tm->tm_year))
 491     return 0;
 492
 493   __daylight = timer >= tz_rules[0].change && timer < tz_rules[1].change;
 494   __timezone = tz_rules[__daylight ? 1 : 0].offset;
 495   __tzname[0] = (char *) tz_rules[0].name;
 496   __tzname[1] = (char *) tz_rules[1].name;
 497
 498   {
 499     /* Keep __tzname_cur_max up to date.  */
 500     size_t len0 = strlen (__tzname[0]);
 501     size_t len1 = strlen (__tzname[1]);
 502     if (len0 > __tzname_cur_max)
 503       __tzname_cur_max = len0;
 504     if (len1 > __tzname_cur_max)
 505       __tzname_cur_max = len1;
 506   }
 507
 508   return 1;
 509 }
 510 \f
 511 #include <libc-lock.h>
 512
 513 /* This locks all the state variables in tzfile.c and this file.  */
 514 __libc_lock_define (, __tzset_lock)
 515
 516 /* Reinterpret the TZ environment variable and set `tzname'.  */
 517 #undef tzset
 518
 519 void
 520 __tzset (void)
 521 {
 522   __libc_lock_lock (__tzset_lock);
 523
 524   __tzset_internal (1);
 525
 526   if (!__use_tzfile)
 527     {
 528       /* Set `tzname'.  */
 529       __tzname[0] = (char *) tz_rules[0].name;
 530       __tzname[1] = (char *) tz_rules[1].name;
 531     }
 532
 533   __libc_lock_unlock (__tzset_lock);
 534 }
 535 weak_alias (__tzset, tzset)