[manpage_begin cksum n 1.1.3]
[copyright {2002, Pat Thoyts}]
[moddesc   {Cyclic Redundancy Checks}]
[titledesc {Calculate a cksum(1) compatible checksum}]
[category  {Hashes, checksums, and encryption}]
[require Tcl 8.2]
[require cksum [opt 1.1.3]]
[description]
[para]

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.

[section COMMANDS]

[list_begin definitions]

[call [cmd "::crc::cksum"] \
        [opt [arg "-format format"]] \
        [opt [arg "-chunksize size"]] \
        [lb] [arg "-channel chan"] | \
        [arg "-filename file"] | [arg "string" ] [rb]]

The command takes string data or a channel or file name and returns a
checksum value calculated using the [syscmd cksum(1)] algorithm. The
result is formatted using the [arg format](n) specifier provided or as
an unsigned integer (%u) by default.

[list_end]

[section OPTIONS]

[list_begin definitions]

[def "-channel [arg name]"]

Return a checksum for the data read from a channel. The command will
read data from the channel until the [cmd "eof"] is true. If you need
to be able to process events during this calculation see the
[sectref {PROGRAMMING INTERFACE}] section

[def "-filename [arg name]"]

This is a convenience option that opens the specified file, sets the
encoding to binary and then acts as if the [arg -channel] option had
been used. The file is closed on completion.

[def "-format [arg string]"]

Return the checksum using an alternative format template.

[list_end]

[section {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 [cmd fileevent] handler in discrete chunks. This can improve
the interactive nature of a GUI application and can help to avoid
excessive memory consumption.

[list_begin definitions]

[call [cmd "::crc::CksumInit"]]

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.

[call [cmd "::crc::CksumUpdate"] [arg "token"] [arg "data"]]

Add data to the checksum identified by token. Calling 
[emph {CksumUpdate $token "abcd"}] is equivalent to calling
[emph {CksumUpdate $token "ab"}] followed by 
[emph {CksumUpdate $token "cb"}]. See [sectref {EXAMPLES}].


[call [cmd "::crc::CksumFinal"] [arg "token"]]

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.

[list_end]

[section EXAMPLES]

[para]
[example {
% crc::cksum "Hello, World!"
2609532967
}]

[para]
[example {
% crc::cksum -format 0x%X "Hello, World!"
0x9B8A5027
}]

[para]
[example {
% crc::cksum -file cksum.tcl
1828321145
}]

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


[see_also sum(n) crc32(n)]
[section AUTHORS]
Pat Thoyts

[section {BUGS, IDEAS, FEEDBACK}]

This document, and the package it describes, will undoubtedly contain
bugs and other problems.

Please report such in the category [emph crc] of the
[uri {http://sourceforge.net/tracker/?group_id=12883} {Tcllib SF Trackers}].

Please also report any ideas for enhancements you may have for either
package and/or documentation.


[keywords cksum checksum crc crc32 {cyclic redundancy check} {data integrity} security]
[manpage_end]