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Name

::crc::crc32 - Perform a 32bit Cyclic Redundancy Check

Synopsis

package require Tcl 8.2

package require crc32 ?1.0?

::crc::crc32 ?-format string? ?-seed value? ?-implementa_tion procname? message

::crc::crc32 ?-format string? ?-seed value? ?-implementa_tion procname? -filename file

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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 string? ?-seed value? ?-implementation procname? message

::crc::crc32 ?-format string? ?-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 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 -impl 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

Wayland Augur, Pat Thoyts

Keywords

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

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