timezone/tzfile.h

   1 /* Layout and location of TZif files.  */
   2
   3 #ifndef TZFILE_H
   4
   5 #define TZFILE_H
   6
   7 /*
   8 ** This file is in the public domain, so clarified as of
   9 ** 1996-06-05 by Arthur David Olson.
  10 */
  11
  12 /*
  13 ** This header is for use ONLY with the time conversion code.
  14 ** There is no guarantee that it will remain unchanged,
  15 ** or that it will remain at all.
  16 ** Do NOT copy it to any system include directory.
  17 ** Thank you!
  18 */
  19
  20 /*
  21 ** Information about time zone files.
  22 */
  23
  24 #ifndef TZDEFRULES
  25 # define TZDEFRULES "posixrules"
  26 #endif /* !defined TZDEFRULES */
  27
  28
  29 /* See Internet RFC 8536 for more details about the following format.  */
  30
  31 /*
  32 ** Each file begins with. . .
  33 */
  34
  35 #define TZ_MAGIC        "TZif"
  36
  37 struct tzhead {
  38         char    tzh_magic[4];           /* TZ_MAGIC */
  39         char    tzh_version[1];         /* '\0' or '2'-'4' as of 2021 */
  40         char    tzh_reserved[15];       /* reserved; must be zero */
  41         char    tzh_ttisutcnt[4];       /* coded number of trans. time flags */
  42         char    tzh_ttisstdcnt[4];      /* coded number of trans. time flags */
  43         char    tzh_leapcnt[4];         /* coded number of leap seconds */
  44         char    tzh_timecnt[4];         /* coded number of transition times */
  45         char    tzh_typecnt[4];         /* coded number of local time types */
  46         char    tzh_charcnt[4];         /* coded number of abbr. chars */
  47 };
  48
  49 /*
  50 ** . . .followed by. . .
  51 **
  52 **      tzh_timecnt (char [4])s         coded transition times a la time(2)
  53 **      tzh_timecnt (unsigned char)s    types of local time starting at above
  54 **      tzh_typecnt repetitions of
  55 **              one (char [4])          coded UT offset in seconds
  56 **              one (unsigned char)     used to set tm_isdst
  57 **              one (unsigned char)     that's an abbreviation list index
  58 **      tzh_charcnt (char)s             '\0'-terminated zone abbreviations
  59 **      tzh_leapcnt repetitions of
  60 **              one (char [4])          coded leap second transition times
  61 **              one (char [4])          total correction after above
  62 **      tzh_ttisstdcnt (char)s          indexed by type; if 1, transition
  63 **                                      time is standard time, if 0,
  64 **                                      transition time is local (wall clock)
  65 **                                      time; if absent, transition times are
  66 **                                      assumed to be local time
  67 **      tzh_ttisutcnt (char)s           indexed by type; if 1, transition
  68 **                                      time is UT, if 0, transition time is
  69 **                                      local time; if absent, transition
  70 **                                      times are assumed to be local time.
  71 **                                      When this is 1, the corresponding
  72 **                                      std/wall indicator must also be 1.
  73 */
  74
  75 /*
  76 ** If tzh_version is '2' or greater, the above is followed by a second instance
  77 ** of tzhead and a second instance of the data in which each coded transition
  78 ** time uses 8 rather than 4 chars,
  79 ** then a POSIX.1-2017 proleptic TZ string for use in handling
  80 ** instants after the last transition time stored in the file
  81 ** (with nothing between the newlines if there is no POSIX.1-2017
  82 ** representation for such instants).
  83 **
  84 ** If tz_version is '3' or greater, the TZ string can be any POSIX.1-2024
  85 ** proleptic TZ string, which means the above is extended as follows.
  86 ** First, the TZ string's hour offset may range from -167
  87 ** through 167 as compared to the range 0 through 24 required
  88 ** by POSIX.1-2017 and earlier.
  89 ** Second, its DST start time may be January 1 at 00:00 and its stop
  90 ** time December 31 at 24:00 plus the difference between DST and
  91 ** standard time, indicating DST all year.
  92 */
  93
  94 /*
  95 ** In the current implementation, "tzset()" refuses to deal with files that
  96 ** exceed any of the limits below.
  97 */
  98
  99 #ifndef TZ_MAX_TIMES
 100 /* This must be at least 242 for Europe/London with 'zic -b fat'.  */
 101 # define TZ_MAX_TIMES 2000
 102 #endif /* !defined TZ_MAX_TIMES */
 103
 104 #ifndef TZ_MAX_TYPES
 105 /* This must be at least 18 for Europe/Vilnius with 'zic -b fat'.  */
 106 # define TZ_MAX_TYPES 256 /* Limited by what (unsigned char)'s can hold */
 107 #endif /* !defined TZ_MAX_TYPES */
 108
 109 #ifndef TZ_MAX_CHARS
 110 /* This must be at least 40 for America/Anchorage.  */
 111 # define TZ_MAX_CHARS 50        /* Maximum number of abbreviation characters */
 112                                 /* (limited by what unsigned chars can hold) */
 113 #endif /* !defined TZ_MAX_CHARS */
 114
 115 #ifndef TZ_MAX_LEAPS
 116 /* This must be at least 27 for leap seconds from 1972 through mid-2023.
 117    There's a plan to discontinue leap seconds by 2035.  */
 118 # define TZ_MAX_LEAPS 50        /* Maximum number of leap second corrections */
 119 #endif /* !defined TZ_MAX_LEAPS */
 120
 121 #endif /* !defined TZFILE_H */