# crc32(n) 1.0 crc "Cyclic Redundancy Check (crc32)"

## NAME

crc32 - Perform a 32bit Cyclic Redundancy Check

## SYNOPSIS

package require Tcl 8.2
package require crc32 ?1.0?

::crc::crc32 ?-format format? ?-seed value? ?-implementation procname? message
::crc::crc32 ?-format format? ?-seed value? ?-implementation procname? -filename file

## DESCRIPTION

This package provides a Tcl-only implementation of the CRC-32 algorithm based upon information provided at http://www.naaccr.org/standard/crc32/document.html If the Trf package is available then the crc-zlib command is used to perform the calculation.

## COMMANDS

::crc::crc32 ?-format format? ?-seed value? ?-implementation procname? message
::crc::crc32 ?-format format? ?-seed value? ?-implementation procname? -filename file
  The command takes string data or a file name and returns a checksum value calculated using the CRC-32 algorithm. The result is formatted using the format(n) specifier provided or as an unsigned integer (%u) by default.

## OPTIONS

-filename name
  Return a checksum for the file contents instead of for parameter data.
-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 as the Trf command crc-zlib cannot accept a seed value, use of this option will force the use of the Tcl only implementation.
-implementation procname
  This hook is provided to allow users to provide their own implementation (perhaps a C compiled extension) or to explicitly request use of the Tcl only implementation when Trf is installed (by setting -implementation crc::Crc32_tcl. The procedure specfied is called with two parameters. The first is the data to be checksummed and the second is the seed value. A 32bit integer is expected as the result.

## EXAMPLES

    % crc::crc32 "Hello, World!"
    3964322768

    % crc::crc32 -format 0x%X "Hello, World!"
    0xEC4AC3D0

    % crc::crc32 -file crc32.tcl
    483919716

## SEE ALSO

sum(n), cksum(n)

## AUTHORS

Pat Thoyts

## KEYWORDS

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