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crc16(3tcl) Cyclic Redundancy Checks crc16(3tcl) 


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

 




 


DESCRIPTION

This package provides a Tcl-only implementation of the CRC algorithms based upon
  information provided at http://www.microconsultants.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 formatted using the
      format(3tcl) 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
      version. 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 convenience,
      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(3tcl), crc32(3tcl), sum(3tcl)

KEYWORDS

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

CATEGORY

Hashes, checksums, and encryption

COPYRIGHT


Copyright (c) 2002, Pat Thoyts








  

    1.1.1
    crc