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?
::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/stan-
dard/crc32/document.html If either the critcl package or the Trf pack-
age 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 algo-
rithm. 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 use-
ful 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)
Mac OS X 10.8 - Generated Wed Sep 5 19:28:53 CDT 2012