CRC32(3) 1 CRC32(3)crc32 - Calculates the crc32 polynomial of a stringSYNOPSIS
int crc32 (string $str)
DESCRIPTION
Generates the cyclic redundancy checksum polynomial of 32-bit lengths of the $str. This is usually used to validate the integrity of data
being transmitted.
Warning
Because PHP's integer type is signed many crc32 checksums will result in negative integers on 32bit platforms. On 64bit installa-
tions all crc32(3) results will be positive integers though.
So you need to use the "%u" formatter of sprintf(3) or printf(3) to get the string representation of the unsigned crc32(3) checksum
in decimal format.
For a hexadecimal representation of the checksum you can either use the "%x" formatter of sprintf(3) or printf(3) or the dechex(3)
conversion functions, both of these also take care of converting the crc32(3) result to an unsigned integer.
Having 64bit installations also return negative integers for higher result values was considered but would break the hexadecimal
conversion as negatives would get an extra 0xFFFFFFFF######## offset then. As hexadecimal representation seems to be the most common
use case we decided to not break this even if it breaks direct decimal comparisons in about 50% of the cases when moving from 32 to
64bits.
In retrospect having the function return an integer maybe wasn't the best idea and returning a hex string representation right away
(as e.g. md5(3) does) might have been a better plan to begin with.
For a more portable solution you may also consider the generic hash(3). hash("crc32b", $str) will return the same string as
dechex(crc32($str)).
PARAMETERS
o $str
- The data.
RETURN VALUES
Returns the crc32 checksum of $str as an integer.
EXAMPLES
Example #1
Displaying a crc32 checksum
This example shows how to print a converted checksum with the printf(3) function:
<?php
$checksum = crc32("The quick brown fox jumped over the lazy dog.");
printf("%u
", $checksum);
?>
SEE ALSO hash(3), md5(3), sha1(3).
PHP Documentation Group CRC32(3)
Check Out this Related Man Page
crc32(n) Cyclic Redundancy Checks crc32(n)
__________________________________________________________________________________________________________________________________________________NAME
crc32 - Perform a 32bit Cyclic Redundancy Check
SYNOPSIS
package require Tcl 8.2
package require crc32 ?1.3?
::crc::crc32 ?-format format? ?-seed value? [ -channel chan | -filename file | message ]
::crc::Crc32Init ?seed?
::crc::Crc32Update token data
::crc::Crc32Final token
_________________________________________________________________DESCRIPTION
This package provides a Tcl implementation of the CRC-32 algorithm based upon information provided at http://www.naaccr.org/stan-
dard/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.
COMMANDS
::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).
OPTIONS -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. Note that the crc32 algorithm includes a final XOR step. If incremental processing is
desired then this must be undone before using the output of the algorithm as the seed for further processing. A simpler alternative
is to use the PROGRAMMING INTERFACE which is intended for this mode of operation.
PROGRAMMING INTERFACE
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.
EXAMPLES
% 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
AUTHORS
Pat Thoyts
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category crc of
the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883]. Please also report any ideas for enhancements you may have for
either package and/or documentation.
SEE ALSO
cksum(n), crc16(n), sum(n)
KEYWORDS
checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security
CATEGORY
Hashes, checksums, and encryption
COPYRIGHT
Copyright (c) 2002, Pat Thoyts
crc 1.3 crc32(n)