crc16(3tcl) Cyclic Redundancy Checks crc16(3tcl)
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NAME
crc16 - Perform a 16bit Cyclic Redundancy Check
SYNOPSIS
package require Tcl 8.2
package require crc16 ?1.1.3?
::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
-- message
::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
-filename file
::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc-
name? -- message
::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc-
name? -filename file
::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
-- message
::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
-filename file
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DESCRIPTION
This package provides a Tcl-only implementation of the CRC algorithms
based upon information provided at http://www.microconsul-
tants.com/tips/crc/crc.txt There are a number of permutations available
for calculating CRC checksums and this package can handle all of them.
Defaults are set up for the most common cases.
COMMANDS
::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
-- message
::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
-filename file
::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc-
name? -- message
::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc-
name? -filename file
::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
-- message
::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
-filename file
The command takes either string data or a file name and returns
a checksum value calculated using the CRC algorithm. The command
used sets up the CRC polynomial, initial value and bit ordering
for the desired standard checksum calculation. The result is
formatted using the format(3tcl) specifier provided or as an un-
signed integer (%u) by default.
A number of common polynomials are in use with the CRC algorithm
and the most commonly used of these are included in this pack-
age. For convenience each of these has a command alias in the
crc namespace.
It is possible to implement the CRC-32 checksum using this crc16
package as the implementation is sufficiently generic to extend
to 32 bit checksums. As an example this has been done already -
however this is not the fastest method to implement this algo-
rithm in Tcl and a separate crc32 package is available.
OPTIONS
-filename name
Return a checksum for the file contents instead of for parameter
data.
-format string
Return the checksum using an alternative format template.
-seed value
Select an alternative seed value for the CRC calculation. The
default is 0 for the CRC16 calculation and 0xFFFF for the CCITT
version. 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. It is also used for
accumulating a checksum from fragments of a large message (or
file)
-implementation procname
This hook is provided to allow users to provide their own imple-
mentation (perhaps a C compiled extension). The procedure spec-
fied is called with two parameters. The first is the data to be
checksummed and the second is the seed value. An integer is ex-
pected as the result.
The package provides some implementations of standard CRC poly-
nomials for the XMODEM, CCITT and the usual CRC-16 checksum. For
convenience, additional commands have been provided that make
use of these implementations.
-- Terminate option processing. Please note that using the option
termination flag is important when processing data from parame-
ters. If the binary data looks like one of the options given
above then the data will be read as an option if this marker is
not included. Always use the -- option termination flag before
giving the data argument.
EXAMPLES
% crc::crc16 -- "Hello, World!"
64077
% crc::crc-ccitt -- "Hello, World!"
26586
% crc::crc16 -format 0x%X -- "Hello, World!"
0xFA4D
% crc::crc16 -file crc16.tcl
51675
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 out-
put 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(3tcl), crc32(3tcl), sum(3tcl)
KEYWORDS
checksum, cksum, crc, crc16, crc32, cyclic redundancy check, data in-
tegrity, security
CATEGORY
Hashes, checksums, and encryption
COPYRIGHT
Copyright (c) 2002, 2017, Pat Thoyts
tcllib 1.1.3 crc16(3tcl)