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crc16(n) Cyclic Redundancy Checks crc16(n) 





NAME


crc16 - Perform a 16bit Cyclic Redundancy Check






SYNOPSIS


package require Tcl 8.2


package require crc16 ?1.1.4?


::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(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



  

  
Return a checksum for the file contents instead of for parameter
    data.

  

  
Return the checksum using an alternative format template.

  

  
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)

  

  
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.

  

  
--

  
Terminate option processing. Please note that using the option termination
      flag is important when processing data from parameters. If the binary data
      looks like one of the options given above then the data will be read as an
      option if this marker is not included. Always use the -- option
      termination flag before giving the data argument.








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 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), crc32(n), sum(n)






KEYWORDS


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






CATEGORY


Hashes, checksums, and encryption






COPYRIGHT


Copyright (c) 2002, 2017, Pat Thoyts








  

    1.1.4
    tcllib