1. Manuals
  2. Tumbleweed
  3. tcllib
  4. crc32(n)

Scroll to navigation

crc32(n) Cyclic Redundancy Checks crc32(n) 





NAME


crc32 - Perform a 32bit Cyclic Redundancy Check






SYNOPSIS


package require Tcl 8.2


package require crc32 ?1.3.3?


::crc::crc32 ?-format format? ?-seed value? [
    -channel chan | -filename file | message ]


::crc::Crc32Init ?seed?


::crc::Crc32Update token data


::crc::Crc32Final token










DESCRIPTION


This package provides a Tcl implementation of the CRC-32 algorithm
    based upon information provided at
    http://www.naaccr.org/standard/crc32/document.html If either the
    critcl package or the Trf package are available then a
    compiled version may be used internally to accelerate the checksum
    calculation.






COMMANDS



  
::crc::crc32 ?-format format? ?-seed value? [
    -channel chan | -filename file | message ]

  
The command takes either string data or a channel or file name and returns
      a checksum value calculated using the CRC-32 algorithm. The result is
      formatted using the format(n) specifier provided. The default is to
      return the value as an unsigned integer (format %u).








OPTIONS



  

  
Return a checksum for the data read from a channel. The command will read
      data from the channel until the eof is true. If you need to be able
      to process events during this calculation see the PROGRAMMING
      INTERFACE section

  

  
This is a convenience option that opens the specified file, sets the
      encoding to binary and then acts as if the -channel option had been
      used. The file is closed on completion.

  

  
Return the checksum using an alternative format template.

  

  
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 the crc32 algorithm includes a final XOR step. If
      incremental processing is desired then this must be undone before using
      the output of the algorithm as the seed for further processing. A simpler
      alternative is to use the PROGRAMMING INTERFACE which is intended
      for this mode of operation.








PROGRAMMING INTERFACE


The CRC-32 package implements the checksum using a context
    variable to which additional data can be added at any time. This is
    expecially useful in an event based environment such as a Tk application or
    a web server package. Data to be checksummed may be handled incrementally
    during a fileevent handler in discrete chunks. This can improve the
    interactive nature of a GUI application and can help to avoid excessive
    memory consumption.



  
::crc::Crc32Init ?seed?

  
Begins a new CRC32 context. Returns a token ID that must be used for the
      remaining functions. An optional seed may be specified if required.

  
::crc::Crc32Update token data

  
Add data to the checksum identified by token. Calling Crc32Update
      $token "abcd" is equivalent to calling Crc32Update $token
      "ab" followed by Crc32Update $token "cb".
      See EXAMPLES.

  
::crc::Crc32Final token

  
Returns the checksum value and releases any resources held by this token.
      Once this command completes the token will be invalid. The result is a 32
      bit integer value.








EXAMPLES




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









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









% crc::crc32 -file crc32.tcl
483919716









% set tok [crc::Crc32Init]
% crc::Crc32Update $tok "Hello, "
% crc::Crc32Update $tok "World!"
% crc::Crc32Final $tok
3964322768









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), crc16(n), sum(n)






KEYWORDS


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






CATEGORY


Hashes, checksums, and encryption






COPYRIGHT


Copyright (c) 2002, Pat Thoyts








  

    1.3.3
    tcllib