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Diffstat (limited to 'libc/stdtime/tzfile.5')
| -rw-r--r-- | libc/stdtime/tzfile.5 | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/libc/stdtime/tzfile.5 b/libc/stdtime/tzfile.5 new file mode 100644 index 000000000000..6b8768cc9fc5 --- /dev/null +++ b/libc/stdtime/tzfile.5 @@ -0,0 +1,152 @@ +.TH TZFILE 5 +.SH NAME +tzfile \- time zone information +.SH SYNOPSIS +.B +#include <tzfile.h> +.SH DESCRIPTION +The time zone information files used by +.IR tzset (3) +begin with the magic characters "TZif" to identify then as +time zone information files, +followed by a character identifying the version of the file's format +(as of 2005, either an ASCII NUL or a '2') +followed by fifteen bytes containing zeroes reserved for future use, +followed by six four-byte values of type +.BR long , +written in a ``standard'' byte order +(the high-order byte of the value is written first). +These values are, +in order: +.TP +.I tzh_ttisgmtcnt +The number of UTC/local indicators stored in the file. +.TP +.I tzh_ttisstdcnt +The number of standard/wall indicators stored in the file. +.TP +.I tzh_leapcnt +The number of leap seconds for which data is stored in the file. +.TP +.I tzh_timecnt +The number of "transition times" for which data is stored +in the file. +.TP +.I tzh_typecnt +The number of "local time types" for which data is stored +in the file (must not be zero). +.TP +.I tzh_charcnt +The number of characters of "time zone abbreviation strings" +stored in the file. +.PP +The above header is followed by +.I tzh_timecnt +four-byte values of type +.BR long , +sorted in ascending order. +These values are written in ``standard'' byte order. +Each is used as a transition time (as returned by +.IR time (2)) +at which the rules for computing local time change. +Next come +.I tzh_timecnt +one-byte values of type +.BR "unsigned char" ; +each one tells which of the different types of ``local time'' types +described in the file is associated with the same-indexed transition time. +These values serve as indices into an array of +.I ttinfo +structures (with +.I tzh_typecnt +entries) that appears next in the file; +these structures are defined as follows: +.in +.5i +.sp +.nf +.ta .5i +\w'unsigned int\0\0'u +struct ttinfo { + long tt_gmtoff; + int tt_isdst; + unsigned int tt_abbrind; +}; +.in -.5i +.fi +.sp +Each structure is written as a four-byte value for +.I tt_gmtoff +of type +.BR long , +in a standard byte order, followed by a one-byte value for +.I tt_isdst +and a one-byte value for +.IR tt_abbrind . +In each structure, +.I tt_gmtoff +gives the number of seconds to be added to UTC, +.I tt_isdst +tells whether +.I tm_isdst +should be set by +.I localtime (3) +and +.I tt_abbrind +serves as an index into the array of time zone abbreviation characters +that follow the +.I ttinfo +structure(s) in the file. +.PP +Then there are +.I tzh_leapcnt +pairs of four-byte values, written in standard byte order; +the first value of each pair gives the time +(as returned by +.IR time(2)) +at which a leap second occurs; +the second gives the +.I total +number of leap seconds to be applied after the given time. +The pairs of values are sorted in ascending order by time. +.PP +Then there are +.I 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. +.PP +Finally there are +.I tzh_ttisgmtcnt +UTC/local indicators, each stored as a one-byte value; +they tell whether the transition times associated with local time types +were specified as UTC or local time, +and are used when a time zone file is used in handling POSIX-style +time zone environment variables. +.PP +.I Localtime +uses the first standard-time +.I ttinfo +structure in the file +(or simply the first +.I ttinfo +structure in the absence of a standard-time structure) +if either +.I tzh_timecnt +is zero or the time argument is less than the first transition time recorded +in the file. +.PP +For version-2-format time zone files, +the above header and data is followed by a second header and data, +identical in format except that +eight bytes are used for each transition time or leap second time. +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). +.SH SEE ALSO +newctime(3) +.\" @(#)tzfile.5 8.2 +.\" This file is in the public domain, so clarified as of +.\" 1996-06-05 by Arthur David Olson. |