NAME¶
crc16 - Perform a 16bit Cyclic Redundancy Check
SYNOPSIS¶
package require
Tcl 8.2
package require
crc16 ?1.1.2?
::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
procname?
message
::crc::crc-ccitt ?-format
format? ?-seed
value?
?-implementation
procname? -filename
file
::crc::xmodem ?-format
format? ?-seed
value?
?-implementation
procname?
message
::crc::xmodem ?-format
format? ?-seed
value?
?-implementation
procname? -filename
file
DESCRIPTION¶
This package provides a Tcl-only implementation of the CRC algorithms based upon
information provided at
http://www.microconsultants.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 procname? message
- ::crc::crc-ccitt ?-format format? ?-seed value?
?-implementation procname? -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 unsigned 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 package. 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 algorithm 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 implementation
(perhaps a C compiled extension). The procedure specfied is called with
two parameters. The first is the data to be checksummed and the second is
the seed value. An integer is expected as the result.
The package provides some implementations of standard CRC polynomials 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.
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.
SEE ALSO¶
cksum(3tcl), crc32(3tcl), sum(3tcl)
KEYWORDS¶
checksum, cksum, crc, crc16, crc32, cyclic redundancy check, data integrity,
security
CATEGORY¶
Hashes, checksums, and encryption
COPYRIGHT¶
Copyright (c) 2002, Pat Thoyts