crc32(n) 1.3 crc "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.
|
% crc::crc32 "Hello, World!"
3964322768
|
|
% crc::crc32 -format 0x%X "Hello, World!"
0xEC4AC3D0
|
|
% crc::crc32 -file crc32.tcl
483919716
|
|
% set tok [crc::Crc32Init]
% crc::Crc32Update $tok "Hello, "
% crc::Crc32Update $tok "World!"
% crc::Crc32Final $tok
3964322768
|
Pat Thoyts
cksum(n), crc16(n), sum(n)
checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security
Copyright © 2002, Pat Thoyts