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ActiveTcl User Guide |
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crc32(n) 1.3 "Cyclic Redundancy Checks"
crc32 - Perform a 32bit Cyclic Redundancy Check
TABLE OF
CONTENTS
SYNOPSIS
DESCRIPTION
COMMANDS
OPTIONS
PROGRAMMING INTERFACE
EXAMPLES
AUTHORS
SEE ALSO
KEYWORDS
COPYRIGHT
package require Tcl 8.2
package require crc32 ?1.3?
This package provides a Tcl implementation of the CRC-32
algorithm based upon information provided at
http://www.naaccr.org/standard/crc32/document.html If either the
critcl package or the Trf package
are available then a compiled version may be used internally to
accelerate the checksum calculation.
- ::crc::crc32 ?-format format? ?-seed value? [ -channel chan | -filename file | message ]
- The command takes either string data or a channel or file name
and returns a checksum value calculated using the CRC-32 algorithm.
The result is formatted using the format(n)
specifier provided. The default is to return the value as an
unsigned integer (format %u).
- -channel name
- Return a checksum for the data read from a channel. The command
will read data from the channel until the eof is
true. If you need to be able to process events during this
calculation see the PROGRAMMING
INTERFACE section
- -filename name
- This is a convenience option that opens the specified file,
sets the encoding to binary and then acts as if the -channel option had been used. The file is closed on
completion.
- -format string
- Return the checksum using an alternative format template.
- -seed value
- Select an alternative seed value for the CRC calculation. The
default is 0xffffffff. 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.
The CRC-32 package implements the checksum using a context
variable to which additional data can be added at any time. This is
expecially useful in an event based environment such as a Tk
application or a web server package. Data to be checksummed may be
handled incrementally during a fileevent handler
in discrete chunks. This can improve the interactive nature of a
GUI application and can help to avoid excessive memory
consumption.
- ::crc::Crc32Init ?seed?
- Begins a new CRC32 context. Returns a token ID that must be
used for the remaining functions. An optional seed may be specified
if required.
- ::crc::Crc32Update token data
- Add data to the checksum identified by token. Calling
Crc32Update $token "abcd" is equivalent to calling
Crc32Update $token "ab" followed by Crc32Update $token
"cb". See EXAMPLES.
- ::crc::Crc32Final token
- Returns the checksum value and releases any resources held by
this token. Once this command completes the token will be invalid.
The result is a 32 bit integer value.
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% crc::crc32 "Hello, World!"
3964322768
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% crc::crc32 -format 0x%X "Hello, World!"
0xEC4AC3D0
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% crc::crc32 -file crc32.tcl
483919716
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% set tok [crc::Crc32Init]
% crc::Crc32Update $tok "Hello, "
% crc::Crc32Update $tok "World!"
% crc::Crc32Final $tok
3964322768
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Pat Thoyts
cksum(n) , crc16(n) , sum(n)
checksum , cksum , crc , crc32 , cyclic redundancy check , data integrity , security
Copyright © 2002, Pat Thoyts