tzfile.h

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/* Layout and location of TZif files.  */
 
#ifndef TZFILE_H
 
#define TZFILE_H
 
/*
 * This file is in the public domain, so clarified as of
 * 1996-06-05 by Arthur David Olson.
 *
 * IDENTIFICATION
 *    src/timezone/tzfile.h
 */
 
/*
 * This header is for use ONLY with the time conversion code.
 * There is no guarantee that it will remain unchanged,
 * or that it will remain at all.
 * Do NOT copy it to any system include directory.
 * Thank you!
 */
 
/*
 * Information about time zone files.
 * See Internet RFC 9636 for more details about the following format.
 */
 
/*
 * Each file begins with. . .
 */
 
#define TZ_MAGIC "TZif"
 
struct tzhead
{
    char        tzh_magic[4];   /* TZ_MAGIC */
    char        tzh_version[1]; /* '\0' or '2'-'4' as of 2021 */
    char        tzh_reserved[15];   /* reserved; must be zero */
    char        tzh_ttisutcnt[4];   /* coded number of trans. time flags */
    char        tzh_ttisstdcnt[4];  /* coded number of trans. time flags */
    char        tzh_leapcnt[4]; /* coded number of leap seconds */
    char        tzh_timecnt[4]; /* coded number of transition times */
    char        tzh_typecnt[4]; /* coded number of local time types */
    char        tzh_charcnt[4]; /* coded number of abbr. chars */
};
 
/*
 * . . .followed by. . .
 *
 *  tzh_timecnt (char [4])s     coded transition times a la time(2)
 *  tzh_timecnt (unsigned char)s    types of local time starting at above
 *  tzh_typecnt repetitions of
 *      one (char [4])      coded UT offset in seconds
 *      one (unsigned char) used to set tm_isdst
 *      one (unsigned char) that's an abbreviation list index
 *  tzh_charcnt (char)s     '\0'-terminated zone abbreviations
 *  tzh_leapcnt repetitions of
 *      one (char [4])      coded leap second transition times
 *      one (char [4])      total correction after above
 *  tzh_ttisstdcnt (char)s      indexed by type; if 1, transition
 *                  time is standard time, if 0,
 *                  transition time is local (wall clock)
 *                  time; if absent, transition times are
 *                  assumed to be local time
 *  tzh_ttisutcnt (char)s       indexed by type; if 1, transition
 *                  time is UT, if 0, transition time is
 *                  local time; if absent, transition
 *                  times are assumed to be local time.
 *                  When this is 1, the corresponding
 *                  std/wall indicator must also be 1.
 */
 
/*
 * If tzh_version is '2' or greater, the above is followed by a second instance
 * of tzhead and a second instance of the data in which each coded transition
 * time uses 8 rather than 4 chars,
 * then a POSIX.1-2017 proleptic TZ string for use in handling
 * instants after the last transition time stored in the file
 * (with nothing between the newlines if there is no POSIX.1-2017
 * representation for such instants).
 *
 * If tz_version is '3' or greater, the TZ string can be any POSIX.1-2024
 * proleptic TZ string, which means the above is extended as follows.
 * First, the TZ string's hour offset may range from -167
 * through 167 as compared to the range 0 through 24 required
 * by POSIX.1-2017 and earlier.
 * Second, its DST start time may be January 1 at 00:00 and its stop
 * time December 31 at 24:00 plus the difference between DST and
 * standard time, indicating DST all year.
 */
 
/*
 * In the current implementation, "tzset()" refuses to deal with files that
 * exceed any of the limits below.
 */
 
#ifndef TZ_MAX_TIMES
/*
 * The following limit applies to localtime.c; zic has no such limit.
 * The limit must be at least 310 for Asia/Hebron with 'zic -b fat'.
 */
#define TZ_MAX_TIMES 2000
#endif                          /* !defined TZ_MAX_TIMES */
 
#ifndef TZ_MAX_TYPES
/* This must be at least 18 for Europe/Vilnius with 'zic -b fat'.  */
#define TZ_MAX_TYPES 256        /* Limited to 256 by Internet RFC 9636.  */
#endif                          /* !defined TZ_MAX_TYPES */
 
#ifndef TZ_MAX_CHARS
/* This must be at least 40 for America/Anchorage.  */
#define TZ_MAX_CHARS 256        /* Maximum number of abbreviation characters */
 /* (limited to 256 by Internet RFC 9636) */
#endif                          /* !defined TZ_MAX_CHARS */
 
#ifndef TZ_MAX_LEAPS
/*
 * The following limit applies to localtime.c; zic has no such limit.
 * The limit must be at least 27 for leap seconds from 1972 through mid-2023.
 * There's a plan to discontinue leap seconds by 2035.
 */
#define TZ_MAX_LEAPS 50         /* Maximum number of leap second corrections */
#endif                          /* !defined TZ_MAX_LEAPS */
 
#endif                          /* !defined TZFILE_H */