+.\" Copyright (c) 1991 The Regents of the University of California.
+.\" All rights reserved.
+.\"
+.\" This code is derived from software contributed to Berkeley by
+.\" Arthur David Olson of the National Cancer Institute.
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\" notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\" notice, this list of conditions and the following disclaimer in the
+.\" documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\" must display the following acknowledgement:
+.\" This product includes software developed by the University of
+.\" California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\" may be used to endorse or promote products derived from this software
+.\" without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" @(#)tzfile.5 5.3 (Berkeley) 5/10/91
+.\"
+.Dd May 10, 1991
+.Dt TZFILE 5
+.Sh NAME
+.Nm tzfile
+.Nd time zone information
+.Sh SYNOPSIS
+.Fd #include <tzfile.h>
+.Sh DESCRIPTION
+The time zone information files used by
+.Xr tzset 3
+begin with bytes reserved for future use,
+followed by four four-byte values of type
+.Em long ,
+written in a ``standard'' byte order
+(the high-order byte of the value is written first).
+These values are,
+in order:
+.Bl -tag -width tzh_ttisstdcnt
+.It Fa tzh_ttisstdcnt
+The number of standard/wall indicators stored in the file.
+.It Fa tzh_leapcnt
+The number of leap seconds for which data is stored in the file.
+.It Fa tzh_timecnt
+The number of "transition times" for which data is stored
+in the file.
+.It Fa tzh_typecnt
+The number of "local time types" for which data is stored
+in the file (must not be zero).
+.It Fa tzh_charcnt
+The number of characters of "time zone abbreviation strings"
+stored in the file.
+.El
+.Pp
+The above header is followed by
+.Fa tzh_timecnt
+four-byte values of type
+.Em long ,
+sorted in ascending order.
+These values are written in ``standard'' byte order.
+Each is used as a transition time (as returned by
+.Xr time 2 )
+at which the rules for computing local time change.
+Next come
+.Fa tzh_timecnt
+one-byte values of type
+.Fa 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
+.Fa ttinfo
+structures that appears next in the file;
+these structures are defined as follows:
+.Bd -literal -offset indent
+struct ttinfo {
+ long tt_gmtoff;
+ int tt_isdst;
+ unsigned int tt_abbrind;
+};
+.Ed
+.Pp
+Each structure is written as a four-byte value for
+.Fa tt_gmtoff
+of type
+.Em long ,
+in a standard byte order, followed by a one-byte value for
+.Fa tt_isdst
+and a one-byte value for
+.Fa tt_abbrind .
+In each structure,
+.Fa tt_gmtoff
+gives the number of seconds to be added to GMT,
+.Fa tt_isdst
+tells whether
+.Fa tm_isdst
+should be set by
+.Xr localtime 3
+and
+.Fa tt_abbrind
+serves as an index into the array of time zone abbreviation characters
+that follow the
+.Fa ttinfo
+structure(s) in the file.
+.Pp
+Then there are
+.Fa 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 2 )
+at which a leap second occurs;
+the second gives the
+.Em total
+number of leap seconds to be applied after the given time.
+The pairs of values are sorted in ascending order by time.
+.Pp
+Finally there are
+.Fa 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
+.Tn POSIX Ns -style
+time zone environment variables.
+.Pp
+.Fa Localtime
+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
+.Fa tzh_timecnt
+is zero or the time argument is less than the first transition time recorded
+in the file.
+.Sh SEE ALSO
+.Xr ctime 3
+.Sh HISTORY
+The
+.Nm tzfile
+file format appeared in
+.Bx 4.3 tahoe.
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