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?
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
31 accelerate 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
40 integer (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
65 The CRC-32 package implements the checksum using a context variable to
66 which additional data can be added at any time. This is expecially use‐
67 ful in an event based environment such as a Tk application or a web
68 server package. Data to be checksummed may be handled incrementally
69 during a fileevent handler in discrete chunks. This can improve the
70 interactive nature of a GUI application and can help to avoid excessive
71 memory consumption.
72 ::crc::Crc32Init ?seed?
74 Begins a new CRC32 context. Returns a token ID that must be used
75 for the remaining functions. An optional seed may be specified
76 if required.
77 ::crc::Crc32Update token data
79 Add data to the checksum identified by token. Calling
80 Crc32Update $token "abcd" is equivalent to calling Crc32Update
81 $token "ab" followed by Crc32Update $token "cb". See EXAMPLES.
82 ::crc::Crc32Final token
84 Returns the checksum value and releases any resources held by
85 this token. Once this command completes the token will be
86 invalid. The result is a 32 bit integer value.
87
89 % crc::crc32 "Hello, World!"
90 3964322768
91 % crc::crc32 -format 0x%X "Hello, World!"
94 0xEC4AC3D0
95 % crc::crc32 -file crc32.tcl
98 483919716
99 % set tok [crc::Crc32Init]
102 % crc::Crc32Update $tok "Hello, "
103 % crc::Crc32Update $tok "World!"
104 % crc::Crc32Final $tok
105 3964322768
106
109 Pat Thoyts
110
112 This document, and the package it describes, will undoubtedly contain
113 bugs and other problems. Please report such in the category crc of the
114 Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883].
115 Please also report any ideas for enhancements you may have for either
116 package and/or documentation.
117
119 cksum(n), crc16(n), sum(n)
120
122 checksum, cksum, crc, crc32, cyclic redundancy check, data integrity,
123 security
124
126 Copyright (c) 2002, Pat Thoyts
127crc 1.3 crc32(n)