[//000000001]: # (crc32 \- Cyclic Redundancy Checks) [//000000002]: # (Generated from file 'crc32\.man' by tcllib/doctools with format 'markdown') [//000000003]: # (Copyright © 2002, Pat Thoyts) [//000000004]: # (crc32\(n\) 1\.3\.3 tcllib "Cyclic Redundancy Checks")
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# NAME crc32 \- Perform a 32bit Cyclic Redundancy Check # Table Of Contents - [Table Of Contents](#toc) - [Synopsis](#synopsis) - [Description](#section1) - [COMMANDS](#section2) - [OPTIONS](#section3) - [PROGRAMMING INTERFACE](#section4) - [EXAMPLES](#section5) - [AUTHORS](#section6) - [Bugs, Ideas, Feedback](#section7) - [See Also](#seealso) - [Keywords](#keywords) - [Category](#category) - [Copyright](#copyright) # SYNOPSIS package require Tcl 8\.2 package require crc32 ?1\.3\.3? [__::crc::crc32__ ?\-format *format*? ?\-seed *value*? \[ *\-channel chan* | *\-filename file* | *message* \]](#1) [__::crc::Crc32Init__ ?*seed*?](#2) [__::crc::Crc32Update__ *token* *data*](#3) [__::crc::Crc32Final__ *token*](#4) # DESCRIPTION This package provides a Tcl implementation of the CRC\-32 algorithm based upon information provided at http://www\.naaccr\.org/standard/crc32/document\.html If either the __critcl__ package or the __Trf__ package are available then a compiled version may be used internally to accelerate the checksum calculation\. # COMMANDS - __::crc::crc32__ ?\-format *format*? ?\-seed *value*? \[ *\-channel chan* | *\-filename file* | *message* \] The command takes either string data or a channel or file name and returns a checksum value calculated using the CRC\-32 algorithm\. The result is formatted using the *format*\(n\) specifier provided\. The default is to return the value as an unsigned integer \(format %u\)\. # 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](#section4) 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\. - \-seed *value* Select an alternative seed value for the CRC calculation\. The default is 0xffffffff\. This can be useful for calculating the CRC for data structures without first converting the whole structure into a string\. The CRC of the previous member can be used as the seed for calculating the CRC of the next member\. Note that the crc32 algorithm includes a final XOR step\. If incremental processing is desired then this must be undone before using the output of the algorithm as the seed for further processing\. A simpler alternative is to use the [PROGRAMMING INTERFACE](#section4) which is intended for this mode of operation\. # PROGRAMMING INTERFACE The CRC\-32 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::Crc32Init__ ?*seed*? Begins a new CRC32 context\. Returns a token ID that must be used for the remaining functions\. An optional seed may be specified if required\. - __::crc::Crc32Update__ *token* *data* Add data to the checksum identified by token\. Calling *Crc32Update $token "abcd"* is equivalent to calling *Crc32Update $token "ab"* followed by *Crc32Update $token "cb"*\. See [EXAMPLES](#section5)\. - __::crc::Crc32Final__ *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::crc32 "Hello, World!" 3964322768 % crc::crc32 -format 0x%X "Hello, World!" 0xEC4AC3D0 % crc::crc32 -file crc32.tcl 483919716 % set tok [crc::Crc32Init] % crc::Crc32Update $tok "Hello, " % crc::Crc32Update $tok "World!" % crc::Crc32Final $tok 3964322768 # AUTHORS Pat Thoyts # Bugs, Ideas, Feedback This document, and the package it describes, will undoubtedly contain bugs and other problems\. Please report such in the category *crc* of the [Tcllib Trackers](http://core\.tcl\.tk/tcllib/reportlist)\. Please also report any ideas for enhancements you may have for either package and/or documentation\. When proposing code changes, please provide *unified diffs*, i\.e the output of __diff \-u__\. Note further that *attachments* are strongly preferred over inlined patches\. Attachments can be made by going to the __Edit__ form of the ticket immediately after its creation, and then using the left\-most button in the secondary navigation bar\. # SEE ALSO [cksum\(n\)](cksum\.md), [crc16\(n\)](crc16\.md), [sum\(n\)](sum\.md) # KEYWORDS [checksum](\.\./\.\./\.\./\.\./index\.md\#checksum), [cksum](\.\./\.\./\.\./\.\./index\.md\#cksum), [crc](\.\./\.\./\.\./\.\./index\.md\#crc), [crc32](\.\./\.\./\.\./\.\./index\.md\#crc32), [cyclic redundancy check](\.\./\.\./\.\./\.\./index\.md\#cyclic\_redundancy\_check), [data integrity](\.\./\.\./\.\./\.\./index\.md\#data\_integrity), [security](\.\./\.\./\.\./\.\./index\.md\#security) # CATEGORY Hashes, checksums, and encryption # COPYRIGHT Copyright © 2002, Pat Thoyts