crc32(n)                    Cyclic Redundancy Checks                    crc32(n)


       crc32 - Perform a 32bit Cyclic Redundancy Check

       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


       This package provides a Tcl implementation of the CRC-32 algorithm based
       upon information provided at If either the critcl
       package or the Trf package are available then a compiled version may be
       used internally to accelerate the checksum calculation.

       ::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

       -channel name
              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

       -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 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.

       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

       ::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

       ::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.


       % crc::crc32 "Hello, World!"

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

       % crc::crc32 -file crc32.tcl

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

       Pat Thoyts

       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 [].
       Please also report any ideas for enhancements you may have for either
       package and/or documentation.

       cksum(n), crc16(n), sum(n)

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

       Hashes, checksums, and encryption

       Copyright (c) 2002, Pat Thoyts

crc                                    1.3                              crc32(n)