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[manpage_begin cksum n 1.1.1]
[copyright {2002, Pat Thoyts}]
[moddesc {Cyclic Redundancy Checks}]
[titledesc {Calculate a cksum(1) compatible checksum}]
[require Tcl 8.2]
[require cksum [opt 1.1.1]]
[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]
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