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crc32(n)                                  Cyclic Redundancy Checks                                  crc32(n)



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NAME
       crc32 - Perform a 32bit Cyclic Redundancy Check

SYNOPSIS
       package require Tcl  8.2

       package require crc32  ?1.3?

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

       ::crc::Crc32Init ?seed?

       ::crc::Crc32Update token data

       ::crc::Crc32Final token

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

       -filename name
              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.

       -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 calculat-ing calculating
              ing the CRC of the next member.


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  han-dler handler
       dler 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   SF   Trackers   [http://source-
       forge.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), crc16(n), sum(n)

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

COPYRIGHT
       Copyright (c) 2002, Pat Thoyts




crc                                                  1.3                                            crc32(n)