'\"
'\" Generated from file '/usr/obj/ports/tcllib-1.11.1/tcllib-1.11.1/modules/crc/cksum.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2002, Pat Thoyts
'\"
'\" The definitions below are for supplemental macros used in Tcl/Tk
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.TH "cksum" n 1.1.2 crc "Cyclic Redundancy Checks"
.BS
.SH NAME
cksum \- Calculate a cksum(1) compatible checksum
.SH SYNOPSIS
package require \fBTcl  8.2\fR
.sp
package require \fBcksum  ?1.1.2?\fR
.sp
\fB::crc::cksum\fR ?\fI-format format\fR? ?\fI-chunksize size\fR? [ \fI-channel chan\fR | \fI-filename file\fR | \fIstring\fR ]
.sp
\fB::crc::CksumInit\fR
.sp
\fB::crc::CksumUpdate\fR \fItoken\fR \fIdata\fR
.sp
\fB::crc::CksumFinal\fR \fItoken\fR
.sp
.BE
.SH DESCRIPTION
.PP
This package provides a Tcl implementation of the cksum(1) algorithm
based upon information provided at in the GNU implementation of this
program as part of the GNU Textutils 2.0 package.
.SH COMMANDS
.TP
\fB::crc::cksum\fR ?\fI-format format\fR? ?\fI-chunksize size\fR? [ \fI-channel chan\fR | \fI-filename file\fR | \fIstring\fR ]
The command takes string data or a channel or file name and returns a
checksum value calculated using the \fBcksum(1)\fR algorithm. The
result is formatted using the \fIformat\fR(n) specifier provided or as
an unsigned integer (%u) by default.
.PP
.SH OPTIONS
.TP
-channel \fIname\fR
Return a checksum for the data read from a channel. The command will
read data from the channel until the \fBeof\fR is true. If you need
to be able to process events during this calculation see the
\fBPROGRAMMING INTERFACE\fR section
.TP
-filename \fIname\fR
This is a convenience option that opens the specified file, sets the
encoding to binary and then acts as if the \fI-channel\fR option had
been used. The file is closed on completion.
.TP
-format \fIstring\fR
Return the checksum using an alternative format template.
.PP
.SH "PROGRAMMING INTERFACE"
The cksum package implements the checksum using a context variable to
which additional data can be added at any time. This is expecially
useful in an event based environment such as a Tk application or a web
server package. Data to be checksummed may be handled incrementally
during a \fBfileevent\fR handler in discrete chunks. This can improve
the interactive nature of a GUI application and can help to avoid
excessive memory consumption.
.TP
\fB::crc::CksumInit\fR
Begins a new cksum context. Returns a token ID that must be used for the
remaining functions. An optional seed may be specified if required.
.TP
\fB::crc::CksumUpdate\fR \fItoken\fR \fIdata\fR
Add data to the checksum identified by token. Calling
\fICksumUpdate $token "abcd"\fR is equivalent to calling
\fICksumUpdate $token "ab"\fR followed by
\fICksumUpdate $token "cb"\fR. See \fBEXAMPLES\fR.
.TP
\fB::crc::CksumFinal\fR \fItoken\fR
Returns the checksum value and releases any resources held by this
token. Once this command completes the token will be invalid. The
result is a 32 bit integer value.
.PP
.SH EXAMPLES
.PP
.nf

% crc::cksum "Hello, World!"
2609532967

.fi
.PP
.nf

% crc::cksum -format 0x%X "Hello, World!"
0x9B8A5027

.fi
.PP
.nf

% crc::cksum -file cksum.tcl
1828321145

.fi
.PP
.nf

% set tok [crc::CksumInit]
% crc::CksumUpdate $tok "Hello, "
% crc::CksumUpdate $tok "World!"
% crc::CksumFinal $tok
2609532967

.fi
.SH AUTHORS
Pat Thoyts
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems.
Please report such in the category \fIcrc\fR of the
\fITcllib SF Trackers\fR [http://sourceforge.net/tracker/?group_id=12883].
Please also report any ideas for enhancements you may have for either
package and/or documentation.
.SH "SEE ALSO"
crc32(n), sum(n)
.SH KEYWORDS
checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security
.SH COPYRIGHT
.nf
Copyright (c) 2002, Pat Thoyts

.fi