1crc32(n) Cyclic Redundancy Checks crc32(n)
2______________________________________________________________________________
6
8 crc32 - Perform a 32bit Cyclic Redundancy Check
9
11 package require Tcl 8.2
12 package require crc32 ?1.3.3?
14 ::crc::crc32 ?-format format? ?-seed value? [ -channel chan | -filename
16 file | message ]
17 ::crc::Crc32Init ?seed?
19 ::crc::Crc32Update token data
21 ::crc::Crc32Final token
23______________________________________________________________________________
25
27 This package provides a Tcl implementation of the CRC-32 algorithm
28 based upon information provided at http://www.naaccr.org/stan‐
29 dard/crc32/document.html If either the critcl package or the Trf pack‐
30 age are available then a compiled version may be used internally to ac‐
31 celerate the checksum calculation.
32
34 ::crc::crc32 ?-format format? ?-seed value? [ -channel chan | -filename
35 file | message ]
36 The command takes either string data or a channel or file name
37 and returns a checksum value calculated using the CRC-32 algo‐
38 rithm. The result is formatted using the format(n) specifier
39 provided. The default is to return the value as an unsigned in‐
40 teger (format %u).
41
43 -channel name
44 Return a checksum for the data read from a channel. The command
45 will read data from the channel until the eof is true. If you
46 need to be able to process events during this calculation see
47 the PROGRAMMING INTERFACE section
48 -filename name
50 This is a convenience option that opens the specified file, sets
51 the encoding to binary and then acts as if the -channel option
52 had been used. The file is closed on completion.
53 -format string
55 Return the checksum using an alternative format template.
56 -seed value
58 Select an alternative seed value for the CRC calculation. The
59 default is 0xffffffff. This can be useful for calculating the
60 CRC for data structures without first converting the whole
61 structure into a string. The CRC of the previous member can be
62 used as the seed for calculating the CRC of the next member.
63 Note that the crc32 algorithm includes a final XOR step. If in‐
64 cremental processing is desired then this must be undone before
65 using the output of the algorithm as the seed for further pro‐
66 cessing. A simpler alternative is to use the PROGRAMMING INTER‐
67 FACE which is intended for this mode of operation.
68
70 The CRC-32 package implements the checksum using a context variable to
71 which additional data can be added at any time. This is expecially use‐
72 ful in an event based environment such as a Tk application or a web
73 server package. Data to be checksummed may be handled incrementally
74 during a fileevent handler in discrete chunks. This can improve the in‐
75 teractive nature of a GUI application and can help to avoid excessive
76 memory consumption.
77 ::crc::Crc32Init ?seed?
79 Begins a new CRC32 context. Returns a token ID that must be used
80 for the remaining functions. An optional seed may be specified
81 if required.
82 ::crc::Crc32Update token data
84 Add data to the checksum identified by token. Calling Crc32Up‐
85 date $token "abcd" is equivalent to calling Crc32Update $token
86 "ab" followed by Crc32Update $token "cb". See EXAMPLES.
87 ::crc::Crc32Final token
89 Returns the checksum value and releases any resources held by
90 this token. Once this command completes the token will be in‐
91 valid. The result is a 32 bit integer value.
92
94 % crc::crc32 "Hello, World!"
95 3964322768
96 % crc::crc32 -format 0x%X "Hello, World!"
99 0xEC4AC3D0
100 % crc::crc32 -file crc32.tcl
103 483919716
104 % set tok [crc::Crc32Init]
107 % crc::Crc32Update $tok "Hello, "
108 % crc::Crc32Update $tok "World!"
109 % crc::Crc32Final $tok
110 3964322768
111
114 Pat Thoyts
115
117 This document, and the package it describes, will undoubtedly contain
118 bugs and other problems. Please report such in the category crc of the
119 Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
120 report any ideas for enhancements you may have for either package
121 and/or documentation.
122 When proposing code changes, please provide unified diffs, i.e the out‐
124 put of diff -u.
125 Note further that attachments are strongly preferred over inlined
127 patches. Attachments can be made by going to the Edit form of the
128 ticket immediately after its creation, and then using the left-most
129 button in the secondary navigation bar.
130
132 cksum(n), crc16(n), sum(n)
133
135 checksum, cksum, crc, crc32, cyclic redundancy check, data integrity,
136 security
137
139 Hashes, checksums, and encryption
140
142 Copyright (c) 2002, Pat Thoyts
143tcllib 1.3.3 crc32(n)