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<?php
/**
* Copyright 2019 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
namespace Google\CRC32;
use Google\CRC32\Builtin;
use Google\CRC32\Google;
use Google\CRC32\PHP;
/**
* Various CRC32 implementations.
*
* ```
* use Google\CRC32\CRC32;
*
* $crc = CRC32::create(CRC32::CASTAGNOLI);
* $crc->update('hello');
*
* echo $crc->hash();
* ```
*/
class CRC32
{
use CRCTrait;
/**
* IEEE polynomial as used by ethernet (IEEE 802.3), v.42, fddi, gzip,
* zip, png, ...
*/
const IEEE = 0xedb88320;
/**
* Castagnoli's polynomial, used in iSCSI, SCTP, Google Cloud Storage,
* Apache Kafka, and has hardware-accelerated in modern intel CPUs.
* https://doi.org/10.1109/26.231911
*/
const CASTAGNOLI = 0x82f63b78;
/**
* Koopman's polynomial.
* https://doi.org/10.1109/DSN.2002.1028931
*/
const KOOPMAN = 0xeb31d82e;
/**
* The size of the checksum in bytes.
*/
const SIZE = 4;
private static $mapping = [
self::IEEE => 'IEEE',
self::CASTAGNOLI => 'Castagnoli',
self::KOOPMAN => 'Koopman',
];
private function __construct()
{
// Prevent instantiation.
}
/**
* Returns the best CRC implementation available on this machine.
*
* @param integer $polynomial The CRC polynomial. Use a 32-bit number,
* or one of the supplied constants, CRC32::IEEE,
* CRC32::CASTAGNOLI, or CRC32::KOOPMAN.
*
* @return CRC32Interface
*/
public static function create($polynomial)
{
if (Google::supports($polynomial) && function_exists('crc32c')) {
return new Google();
}
if (Builtin::supports($polynomial)) {
return new Builtin($polynomial);
}
// Fallback to the pure PHP version
return new PHP($polynomial);
}
/**
* Prints the human friendly name for this polynomial.
*
* @param integer $polynomial The CRC polynomial.
*
* @return string
*/
public static function string($polynomial)
{
if (isset(self::$mapping[$polynomial])) {
return self::$mapping[$polynomial];
}
return '0x' . self::int2hex($polynomial);
}
}
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