SYNOPSIS

package require Tcl 8.2

package require cksum ?1.1.4?

::crc::cksum ?-format format? ?-chunksize size? [ -channel chan | -filename file | string ]

::crc::CksumInit

::crc::CksumUpdate token data

::crc::CksumFinal token

---

DESCRIPTION

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.

COMMANDS

::crc::cksum ?-format format? ?-chunksize size? [ -channel chan | -filename file | string ]

The command takes string data or a channel or file name and returns a checksum value calculated using the cksum(1) algorithm. The result is formatted using the format(3tcl) specifier provided or as an unsigned integer (%u) by default.

OPTIONS

-channel name

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

-filename name

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

-format string

Return the checksum using an alternative format template.

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

::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.

::crc::CksumUpdate token data

Add data to the checksum identified by token. Calling CksumUpdate $token "abcd" is equivalent to calling CksumUpdate $token "ab" followed by CksumUpdate $token "cb". See EXAMPLES.

::crc::CksumFinal 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.

EXAMPLES

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

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

% crc::cksum -file cksum.tcl
1828321145

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

AUTHORS

Pat Thoyts

KEYWORDS

checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security

CATEGORY

Hashes, checksums, and encryption

COPYRIGHT

Copyright (c) 2002, Pat Thoyts