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Revision 1.25, Tue Oct 24 17:38:17 2017 UTC (6 years, 5 months ago) by christos
Welcome to 2017c: zic and the reference runtime now reject multiple leap seconds within 28 days of each other, or leap seconds before the Epoch. As a result, support for double leap seconds, which was obsolescent and undocumented, has been removed. Double leap seconds were an error in the C89 standard; they have never existed in civil timekeeping. (Thanks to Robert Elz and Bradley White for noticing glitches in the code that uncovered this problem.) zic now warns about use of the obsolescent and undocumented -y option, and about use of the obsolescent TYPE field of Rule lines. zic now allows unambiguous abbreviations like "Sa" and "Su" for weekdays; formerly it rejected them due to a bug. Conversely, zic no longer considers non-prefixes to be abbreviations; for example, it no longer accepts "lF" as an abbreviation for "lastFriday". Also, zic warns about the undocumented usage with a "last-" prefix, e.g., "last-Fri". Similarly, zic now accepts the unambiguous abbreviation "L" for "Link" in ordinary context and for "Leap" in leap-second context. Conversely, zic no longer accepts non-prefixes such as "La" as abbreviations for words like "Leap". zic no longer accepts leap second lines in ordinary input, or ordinary lines in leap second input. Formerly, zic sometimes warned about this undocumented usage and handled it incorrectly. The new macro HAVE_TZNAME governs whether the tzname external variable is exported, instead of USG_COMPAT. USG_COMPAT now governs only the external variables "timezone" and "daylight". This change is needed because the three variables are not in the same category: although POSIX requires tzname, it specifies the other two variables as optional. Also, USG_COMPAT is now 1 or 0: if not defined, the code attempts to guess it from other macros. localtime.c and difftime.c no longer require stdio.h, and .c files other than zic.c no longer require sys/wait.h. zdump.c no longer assumes snprintf. (Reported by Jonathan Leffler.) Calculation of time_t extrema works around a bug in GCC 4.8.4 (Reported by Stan Shebs and Joseph Myers.) zic.c no longer mistranslates formats of line numbers in non-English locales. (Problem reported by Benno Schulenberg.) Several minor changes have been made to the code to make it a bit easier to port to MS-Windows and Solaris. (Thanks to Kees Dekker for reporting the problems.) Changes to documentation and commentary The two new files 'theory.html' and 'calendars' contain the contents of the removed file 'Theory'. The goal is to document tzdb theory more accessibly. The zic man page now documents abbreviation rules. tz-link.htm now covers how to apply tzdata changes to clients. (Thanks to Jorge Fábregas for the AIX link.) It also mentions MySQL. The leap-seconds.list URL has been updated to something that is more reliable for tzdb. (Thanks to Tim Parenti and Brian Inglis.) |
.\" $NetBSD: tzfile.5,v 1.25 2017/10/24 17:38:17 christos Exp $ .\" .\" This file is in the public domain, so clarified as of .\" 1996-06-05 by Arthur David Olson (arthur_david_olson@nih.gov). .Dd October 6, 2016 .Dt TZFILE 5 .Os .Sh NAME .Nm tzfile .Nd time zone information .Sh DESCRIPTION The time zone information files used by .Xr tzset 3 are typically found under a directory with a name like .Pa /usr/share/zoneinfo . These files beging with a 44-byte header containing the following fields: .Bl -bullet .It The magic four-byte ASCII sequence begin with the magic characters .Dq TZif . identifies the file as a time zone information file. .It A byte identifying the version of the file's format (as of 2017, either an ASCII .Dv NUL , or .Dq 2 , or .Dq 3 ). .It Fifteen bytes containing zeros reserved for future use. .It Six four-byte integer values written in a standard byte order (the high-order byte of the value is written first). These values are, in order: .Bl -inset .It Va tzh_ttisgmtcnt The number of UT/local indicators stored in the file. .It Va tzh_ttisstdcnt The number of standard/wall indicators stored in the file. .It Va tzh_leapcnt The number of leap seconds for which data entries are stored in the file. .It Va tzh_timecnt The number of transition times for which data entries are stored in the file. .It Va tzh_typecnt The number of local time types for which data entries are stored in the file (must not be zero). .It Va tzh_charcnt The number of bytes of time zone abbreviation strings stored in the file. .El .It The above header is followed by the following fields, whose lengths depend on the contents of the header: .Bl -inset .It Va tzh_timecnt four-byte signed integer values sorted in ascending order. These values are written in These values are written in standard byte order. Each is used as a transition time (as returned by .Xr time 3 ) at which the rules for computing local time change. .It Va tzh_timecnt one-byte unsigned integer values; each one tells which of the different types of local time types described in the file is associated with the time period starting with the same-indexed transition time. These values serve as indices into the next field. .It Va tzh_typecnt .Va ttinfo entries, each defined as follows: .Bd -literal struct ttinfo { int32_t tt_gmtoff; unsigned char tt_isdst; unsigned char tt_abbrind; }; .Ed .Pp Each structure is written as a four-byte signed integer value for .Va tt_gmtoff in a standard byte order, followed by a one-byte value for .Va tt_isdst and a one-byte value for .Va tt_abbrind . In each structure, .Va tt_gmtoff gives the number of seconds to be added to UT, .Va tt_isdst tells whether .Va tm_isdst should be set by .Xr localtime 3 and .Va tt_abbrind serves as an index into the array of time zone abbreviation bytes that follow the .Va ttinfo structure(s) in the file. .It Va tzh_leapcnt pairs of four-byte values, written in standard byte order; the first value of each pair gives the time (as returned by .Xr time 3 ) at which a leap second occurs; the second gives the .Em total number of leap seconds to be applied during the time period starting at the given time. The pairs of values are sorted in ascending order by time. Each transition is for one leap second, either positive or negative; transitions always separated by at least 28 days minus 1 second. .It Va tzh_ttisstdcnt standard/wall indicators, each stored as a one-byte value; they tell whether the transition times associated with local time types were specified as standard time or wall clock time, and are used when a time zone file is used in handling POSIX-style time zone environment variables. .It Va tzh_ttisgmtcnt UT/local indicators, each stored as a one-byte value; they tell whether the transition times associated with local time types were specified as UT or local time, and are used when a time zone file is used in handling POSIX-style time zone environment variables. .Pp The .Xr localtime 3 function uses the first standard-time .Fa ttinfo structure in the file (or simply the first .Fa ttinfo structure in the absence of a standard-time structure) if either .Va tzh_timecnt is zero or the time argument is less than the first transition time recorded in the file. .El .El .Ss Version 2 format For version-2-format time zone files, the above header and data are followed by a second header and data, identical in format except that eight bytes are used for each transition time or leap second time. (Leap second counts remain four bytes.) After the second header and data comes a newline-enclosed, 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). The POSIX-style string must agree with the local time type after both data's last transition times; for example, given the string .Dq WET0WEST,M3.5.0,M10.5.0/3 then if a last transition time is in July, the transition's local time type must specify a daylight-saving time abbreviated .Dq WEST that is one hour east of UT. .Ss Version 3 format For version-3-format time zone files, the POSIX-TZ-style string may use two minor extensions to the POSIX TZ format, as described in .Xr tzset 3 . First, the hours part of its transition times may be signed and range from \-167 through 167 instead of the POSIX-required unsigned values from 0 through 24. Second, DST is in effect all year if it starts January 1 at 00:00 and ends December 31 at 24:00 plus the difference between daylight saving and standard time. .Pp Future changes to the format may append more data. .Sh SEE ALSO .Xr ctime 3 , .Xr localtime 3 , .Xr time 3 , .Xr tzset 3 , .Xr zdump 8 .Xr zic 8 .\" @(#)tzfile.5 8.3 .\" This file is in the public domain, so clarified as of .\" 1996-06-05 by Arthur David Olson.