db/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.
*/

/*
** 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.
*/

#ifndef TZDIR
#define TZDIR   "/usr/local/etc/zoneinfo" /* Time zone object file directory */
#endif /* !defined TZDIR */

#ifndef TZDEFAULT
#define TZDEFAULT       "localtime"
#endif /* !defined TZDEFAULT */

#ifndef TZDEFRULES
#define TZDEFRULES      "posixrules"
#endif /* !defined TZDEFRULES */

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

#define TZ_MAGIC        "TZif"

struct tzhead {
        char    tzh_magic[4];           /* TZ_MAGIC */
        char    tzh_version[1];         /* '\0' or '2' or '3' as of 2013 */
        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 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 wall clock time
**                                      if absent, transition times are
**                                      assumed to be wall clock time
**      tzh_ttisgmtcnt (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
*/

/*
** 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).
**
** If tz_version is '3' or greater, the above is extended as follows.
** First, the POSIX TZ string's hour offset may range from -167
** through 167 as compared to the POSIX-required 0 through 24.
** 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
#define TZ_MAX_TIMES    2000
#endif /* !defined TZ_MAX_TIMES */

#ifndef TZ_MAX_TYPES
/* This must be at least 17 for Europe/Samara and Europe/Vilnius.  */
#define TZ_MAX_TYPES    256 /* Limited by what (unsigned char)'s can hold */
#endif /* !defined TZ_MAX_TYPES */

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

#ifndef TZ_MAX_LEAPS
#define TZ_MAX_LEAPS    50      /* Maximum number of leap second corrections */
#endif /* !defined TZ_MAX_LEAPS */

#define SECSPERMIN      60
#define MINSPERHOUR     60
#define HOURSPERDAY     24
#define DAYSPERWEEK     7
#define DAYSPERNYEAR    365
#define DAYSPERLYEAR    366
#define SECSPERHOUR     (SECSPERMIN * MINSPERHOUR)
#define SECSPERDAY      ((int_fast32_t) 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 */