tzfile.h

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#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.
 */

#define TZDEFAULT   "localtime"
#define TZDEFRULES  "posixrules"

/*
 * Each file begins with. . .
 */

#define TZ_MAGIC    "TZif"

struct tzhead
{
    char        tzh_magic[4];   /* TZ_MAGIC */
    char        tzh_version[1]; /* '\0' or '2' as of 2005 */
    char        tzh_reserved[15];       /* reserved--must be zero */
    char        tzh_ttisgmtcnt[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 UTC 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 TRUE, transition
 *                  time is standard time, if FALSE,
 *                  transition time is wall clock time
 *                  if absent, transition times are
 *                  assumed to be wall clock time
 *  tzh_ttisgmtcnt (char)s      indexed by type; if TRUE, transition
 *                  time is UTC, if FALSE,
 *                  transition time is local time
 *                  if absent, transition times are
 *                  assumed to be local time
 *----------
 */

/*
 * 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-TZ-environment-variable-style 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 representation for
 * such instants).
 */

/*
 * In the current implementation, "tzset()" refuses to deal with files that
 * exceed any of the limits below.
 */

#define TZ_MAX_TIMES    1200

#define TZ_MAX_TYPES    256     /* Limited by what (unsigned char)'s can hold */

#define TZ_MAX_CHARS    50      /* Maximum number of abbreviation characters */
 /* (limited by what unsigned chars can hold) */

#define TZ_MAX_LEAPS    50      /* Maximum number of leap second corrections */

#define SECSPERMIN  60
#define MINSPERHOUR 60
#define HOURSPERDAY 24
#define DAYSPERWEEK 7
#define DAYSPERNYEAR    365
#define DAYSPERLYEAR    366
#define SECSPERHOUR (SECSPERMIN * MINSPERHOUR)
#define SECSPERDAY  ((long) SECSPERHOUR * HOURSPERDAY)
#define MONSPERYEAR 12

#define TM_SUNDAY   0
#define TM_MONDAY   1
#define TM_TUESDAY  2
#define TM_WEDNESDAY    3
#define TM_THURSDAY 4
#define TM_FRIDAY   5
#define TM_SATURDAY 6

#define TM_JANUARY  0
#define TM_FEBRUARY 1
#define TM_MARCH    2
#define TM_APRIL    3
#define TM_MAY      4
#define TM_JUNE     5
#define TM_JULY     6
#define TM_AUGUST   7
#define TM_SEPTEMBER    8
#define TM_OCTOBER  9
#define TM_NOVEMBER 10
#define TM_DECEMBER 11

#define TM_YEAR_BASE    1900

#define EPOCH_YEAR  1970
#define EPOCH_WDAY  TM_THURSDAY

#define isleap(y) (((y) % 4) == 0 && (((y) % 100) != 0 || ((y) % 400) == 0))

/*
 * Since everything in isleap is modulo 400 (or a factor of 400), we know that
 *    isleap(y) == isleap(y % 400)
 * and so
 *    isleap(a + b) == isleap((a + b) % 400)
 * or
 *    isleap(a + b) == isleap(a % 400 + b % 400)
 * This is true even if % means modulo rather than Fortran remainder
 * (which is allowed by C89 but not C99).
 * We use this to avoid addition overflow problems.
 */

#define isleap_sum(a, b)      isleap((a) % 400 + (b) % 400)

#endif   /* !defined TZFILE_H */