crc32
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 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.
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 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(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
crc 1.3 crc32(n)