1crc16(n) Cyclic Redundancy Checks crc16(n)
2______________________________________________________________________________
6
8 crc16 - Perform a 16bit Cyclic Redundancy Check
9
11 package require Tcl 8.2
12 package require crc16 ?1.1.3?
14 ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
16 -- message
17 ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
19 -filename file
20 ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc‐
22 name? -- message
23 ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc‐
25 name? -filename file
26 ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
28 -- message
29 ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
31 -filename file
32______________________________________________________________________________
34
36 This package provides a Tcl-only implementation of the CRC algorithms
37 based upon information provided at http://www.microconsul‐
38 tants.com/tips/crc/crc.txt There are a number of permutations available
39 for calculating CRC checksums and this package can handle all of them.
40 Defaults are set up for the most common cases.
41
43 ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
44 -- message
45 ::crc::crc16 ?-format format? ?-seed value? ?-implementation procname?
47 -filename file
48 ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc‐
50 name? -- message
51 ::crc::crc-ccitt ?-format format? ?-seed value? ?-implementation proc‐
53 name? -filename file
54 ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
56 -- message
57 ::crc::xmodem ?-format format? ?-seed value? ?-implementation procname?
59 -filename file
60 The command takes either string data or a file name and returns
61 a checksum value calculated using the CRC algorithm. The command
62 used sets up the CRC polynomial, initial value and bit ordering
63 for the desired standard checksum calculation. The result is
64 formatted using the format(n) specifier provided or as an
65 unsigned integer (%u) by default.
66 A number of common polynomials are in use with the CRC algorithm
68 and the most commonly used of these are included in this pack‐
69 age. For convenience each of these has a command alias in the
70 crc namespace.
71 It is possible to implement the CRC-32 checksum using this crc16
73 package as the implementation is sufficiently generic to extend
74 to 32 bit checksums. As an example this has been done already -
75 however this is not the fastest method to implement this algo‐
76 rithm in Tcl and a separate crc32 package is available.
77
79 -filename name
80 Return a checksum for the file contents instead of for parameter
81 data.
82 -format string
84 Return the checksum using an alternative format template.
85 -seed value
87 Select an alternative seed value for the CRC calculation. The
88 default is 0 for the CRC16 calculation and 0xFFFF for the CCITT
89 version. This can be useful for calculating the CRC for data
90 structures without first converting the whole structure into a
91 string. The CRC of the previous member can be used as the seed
92 for calculating the CRC of the next member. It is also used for
93 accumulating a checksum from fragments of a large message (or
94 file)
95 -implementation procname
97 This hook is provided to allow users to provide their own imple‐
98 mentation (perhaps a C compiled extension). The procedure spec‐
99 fied is called with two parameters. The first is the data to be
100 checksummed and the second is the seed value. An integer is
101 expected as the result.
102 The package provides some implementations of standard CRC poly‐
104 nomials for the XMODEM, CCITT and the usual CRC-16 checksum. For
105 convenience, additional commands have been provided that make
106 use of these implementations.
107 -- Terminate option processing. Please note that using the option
109 termination flag is important when processing data from parame‐
110 ters. If the binary data looks like one of the options given
111 above then the data will be read as an option if this marker is
112 not included. Always use the -- option termination flag before
113 giving the data argument.
114
116 % crc::crc16 -- "Hello, World!"
117 64077
118 % crc::crc-ccitt -- "Hello, World!"
121 26586
122 % crc::crc16 -format 0x%X -- "Hello, World!"
125 0xFA4D
126 % crc::crc16 -file crc16.tcl
129 51675
130
133 Pat Thoyts
134
136 This document, and the package it describes, will undoubtedly contain
137 bugs and other problems. Please report such in the category crc of the
138 Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
139 report any ideas for enhancements you may have for either package
140 and/or documentation.
141 When proposing code changes, please provide unified diffs, i.e the out‐
143 put of diff -u.
144 Note further that attachments are strongly preferred over inlined
146 patches. Attachments can be made by going to the Edit form of the
147 ticket immediately after its creation, and then using the left-most
148 button in the secondary navigation bar.
149
151 cksum(n), crc32(n), sum(n)
152
154 checksum, cksum, crc, crc16, crc32, cyclic redundancy check, data
155 integrity, security
156
158 Hashes, checksums, and encryption
159
161 Copyright (c) 2002, 2017, Pat Thoyts
162tcllib 1.1.3 crc16(n)