crc16(n)						     Cyclic Redundancy Checks							  crc16(n)

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NAME

       crc16 - Perform a 16bit Cyclic Redundancy Check

SYNOPSIS

       package require Tcl  8.2

       package require crc16  ?1.1.1?

       ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname? message

       ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname? -filename file

       ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation procname? message

       ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation procname? -filename file

       ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname? message

       ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname? -filename file

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DESCRIPTION

       This  package  provides	a  Tcl-only  implementation  of  the  CRC  algorithms  based  upon information provided at http://www.microconsul-
       tants.com/tips/crc/crc.txt There are a number of permutations available for calculating CRC checksums and this package can  handle  all	of
       them. Defaults are set up for the most common cases.

COMMANDS

       ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname? message

       ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname? -filename file

       ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation procname? message

       ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation procname? -filename file

       ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname? message

       ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname? -filename file
	      The  command  takes  either  string data or a file name and returns a checksum value calculated using the CRC algorithm. The command
	      used sets up the CRC polynomial, initial value and bit ordering for the desired standard checksum calculation. The result is format-
	      ted using the format(n) specifier provided or as an unsigned integer (%u) by default.

	      A  number  of common polynomials are in use with the CRC algorithm and the most commonly used of these are included in this package.
	      For convenience each of these has a command alias in the crc namespace.

	      It is possible to implement the CRC-32 checksum using this crc16 package as the implementation is sufficiently generic to extend	to
	      32  bit  checksums. As an example this has been done already - however this is not the fastest method to implement this algorithm in
	      Tcl and a separate crc32 package is available.

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 0 for the CRC16 calculation and 0xFFFF for the  CCITT  ver-
	      sion.   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. It is also used for  accumulating
	      a checksum from fragments of a large message (or file)

       -implementation procname
	      This hook is provided to allow users to provide their own implementation (perhaps a C compiled extension). The procedure specfied is
	      called with two parameters. The first is the data to be checksummed and the second is the seed value. An integer is expected as  the
	      result.

	      The  package provides some implementations of standard CRC polynomials for the XMODEM, CCITT and the usual CRC-16 checksum. For con-
	      venience, additional commands have been provided that make use of these implementations.

EXAMPLES

       % crc::crc16 "Hello, World!"
       64077

       % crc::crc-ccitt "Hello, World!"
       26586

       % crc::crc16 -format 0x%X "Hello, World!"
       0xFA4D

       % crc::crc16 -file crc16.tcl
       51675

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  SF	Trackers [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you may have for
       either package and/or documentation.

SEE ALSO

       cksum(n), crc32(n), sum(n)

KEYWORDS

       checksum, cksum, crc, crc16, crc32, cyclic redundancy check, data integrity, security

COPYRIGHT

       Copyright (c) 2002, Pat Thoyts

crc								       1.1.1								  crc16(n)