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PHP哈希演算法的相關技巧

墨辰丷
發布: 2023-03-29 21:50:01
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1388 人瀏覽過

本篇主要介紹PHP哈希演算法的相關技巧,有興趣的朋友參考下,希望對大家有幫助。

本文實例講述了PHP實作的一致性雜湊演算法。分享給大家供大家參考,具體如下:

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<?php

/**

 * Flexihash - A simple consistent hashing implementation for PHP.

 *

 * The MIT License

 *

 * Copyright (c) 2008 Paul Annesley

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

 * THE SOFTWARE.

 *

 * @author Paul Annesley

 * @link http://paul.annesley.cc/

 * @copyright Paul Annesley, 2008

 * @comment by MyZ (http://blog.csdn.net/mayongzhan)

 */

/**

 * A simple consistent hashing implementation with pluggable hash algorithms.

 *

 * @author Paul Annesley

 * @package Flexihash

 * @licence http://www.opensource.org/licenses/mit-license.php

 */

class Flexihash

{

  /**

   * The number of positions to hash each target to.

   *

   * @var int

   * @comment 虚拟节点数,解决节点分布不均的问题

   */

  private $_replicas = 64;

  /**

   * The hash algorithm, encapsulated in a Flexihash_Hasher implementation.

   * @var object Flexihash_Hasher

   * @comment 使用的hash方法 : md5,crc32

   */

  private $_hasher;

  /**

   * Internal counter for current number of targets.

   * @var int

   * @comment 节点记数器

   */

  private $_targetCount = 0;

  /**

   * Internal map of positions (hash outputs) to targets

   * @var array { position => target, ... }

   * @comment 位置对应节点,用于lookup中根据位置确定要访问的节点

   */

  private $_positionToTarget = array();

  /**

   * Internal map of targets to lists of positions that target is hashed to.

   * @var array { target => [ position, position, ... ], ... }

   * @comment 节点对应位置,用于删除节点

   */

  private $_targetToPositions = array();

  /**

   * Whether the internal map of positions to targets is already sorted.

   * @var boolean

   * @comment 是否已排序

   */

  private $_positionToTargetSorted = false;

  /**

   * Constructor

   * @param object $hasher Flexihash_Hasher

   * @param int $replicas Amount of positions to hash each target to.

   * @comment 构造函数,确定要使用的hash方法和需拟节点数,虚拟节点数越多,分布越均匀,但程序的分布式运算越慢

   */

  public function __construct(Flexihash_Hasher $hasher = null, $replicas = null)

  {

    $this->_hasher = $hasher ? $hasher : new Flexihash_Crc32Hasher();

    if (!empty($replicas)) $this->_replicas = $replicas;

  }

  /**

   * Add a target.

   * @param string $target

   * @chainable

   * @comment 添加节点,根据虚拟节点数,将节点分布到多个虚拟位置上

   */

  public function addTarget($target)

  {

    if (isset($this->_targetToPositions[$target]))

    {

      throw new Flexihash_Exception("Target &#39;$target&#39; already exists.");

    }

    $this->_targetToPositions[$target] = array();

    // hash the target into multiple positions

    for ($i = 0; $i < $this->_replicas; $i++)

    {

      $position = $this->_hasher->hash($target . $i);

      $this->_positionToTarget[$position] = $target; // lookup

      $this->_targetToPositions[$target] []= $position; // target removal

    }

    $this->_positionToTargetSorted = false;

    $this->_targetCount++;

    return $this;

  }

  /**

   * Add a list of targets.

   * @param array $targets

   * @chainable

   */

  public function addTargets($targets)

  {

    foreach ($targets as $target)

    {

      $this->addTarget($target);

    }

    return $this;

  }

  /**

   * Remove a target.

   * @param string $target

   * @chainable

   */

  public function removeTarget($target)

  {

    if (!isset($this->_targetToPositions[$target]))

    {

      throw new Flexihash_Exception("Target &#39;$target&#39; does not exist.");

    }

    foreach ($this->_targetToPositions[$target] as $position)

    {

      unset($this->_positionToTarget[$position]);

    }

    unset($this->_targetToPositions[$target]);

    $this->_targetCount--;

    return $this;

  }

  /**

   * A list of all potential targets

   * @return array

   */

  public function getAllTargets()

  {

    return array_keys($this->_targetToPositions);

  }

  /**

   * Looks up the target for the given resource.

   * @param string $resource

   * @return string

   */

  public function lookup($resource)

  {

    $targets = $this->lookupList($resource, 1);

    if (empty($targets)) throw new Flexihash_Exception(&#39;No targets exist&#39;);

    return $targets[0];

  }

  /**

   * Get a list of targets for the resource, in order of precedence.

   * Up to $requestedCount targets are returned, less if there are fewer in total.

   *

   * @param string $resource

   * @param int $requestedCount The length of the list to return

   * @return array List of targets

   * @comment 查找当前的资源对应的节点,

   *     节点为空则返回空,节点只有一个则返回该节点,

   *     对当前资源进行hash,对所有的位置进行排序,在有序的位置列上寻找当前资源的位置

   *     当全部没有找到的时候,将资源的位置确定为有序位置的第一个(形成一个环)

   *     返回所找到的节点

   */

  public function lookupList($resource, $requestedCount)

  {

    if (!$requestedCount)

      throw new Flexihash_Exception(&#39;Invalid count requested&#39;);

    // handle no targets

    if (empty($this->_positionToTarget))

      return array();

    // optimize single target

    if ($this->_targetCount == 1)

      return array_unique(array_values($this->_positionToTarget));

    // hash resource to a position

    $resourcePosition = $this->_hasher->hash($resource);

    $results = array();

    $collect = false;

    $this->_sortPositionTargets();

    // search values above the resourcePosition

    foreach ($this->_positionToTarget as $key => $value)

    {

      // start collecting targets after passing resource position

      if (!$collect && $key > $resourcePosition)

      {

        $collect = true;

      }

      // only collect the first instance of any target

      if ($collect && !in_array($value, $results))

      {

        $results []= $value;

      }

      // return when enough results, or list exhausted

      if (count($results) == $requestedCount || count($results) == $this->_targetCount)

      {

        return $results;

      }

    }

    // loop to start - search values below the resourcePosition

    foreach ($this->_positionToTarget as $key => $value)

    {

      if (!in_array($value, $results))

      {

        $results []= $value;

      }

      // return when enough results, or list exhausted

      if (count($results) == $requestedCount || count($results) == $this->_targetCount)

      {

        return $results;

      }

    }

    // return results after iterating through both "parts"

    return $results;

  }

  public function __toString()

  {

    return sprintf(

      &#39;%s{targets:[%s]}&#39;,

      get_class($this),

      implode(&#39;,&#39;, $this->getAllTargets())

    );

  }

  // ----------------------------------------

  // private methods

  /**

   * Sorts the internal mapping (positions to targets) by position

   */

  private function _sortPositionTargets()

  {

    // sort by key (position) if not already

    if (!$this->_positionToTargetSorted)

    {

      ksort($this->_positionToTarget, SORT_REGULAR);

      $this->_positionToTargetSorted = true;

    }

  }

}

/**

 * Hashes given values into a sortable fixed size address space.

 *

 * @author Paul Annesley

 * @package Flexihash

 * @licence http://www.opensource.org/licenses/mit-license.php

 */

interface Flexihash_Hasher

{

  /**

   * Hashes the given string into a 32bit address space.

   *

   * Note that the output may be more than 32bits of raw data, for example

   * hexidecimal characters representing a 32bit value.

   *

   * The data must have 0xFFFFFFFF possible values, and be sortable by

   * PHP sort functions using SORT_REGULAR.

   *

   * @param string

   * @return mixed A sortable format with 0xFFFFFFFF possible values

   */

  public function hash($string);

}

/**

 * Uses CRC32 to hash a value into a signed 32bit int address space.

 * Under 32bit PHP this (safely) overflows into negatives ints.

 *

 * @author Paul Annesley

 * @package Flexihash

 * @licence http://www.opensource.org/licenses/mit-license.php

 */

class Flexihash_Crc32Hasher

  implements Flexihash_Hasher

{

  /* (non-phpdoc)

   * @see Flexihash_Hasher::hash()

   */

  public function hash($string)

  {

    return crc32($string);

  }

}

/**

 * Uses CRC32 to hash a value into a 32bit binary string data address space.

 *

 * @author Paul Annesley

 * @package Flexihash

 * @licence http://www.opensource.org/licenses/mit-license.php

 */

class Flexihash_Md5Hasher

  implements Flexihash_Hasher

{

  /* (non-phpdoc)

   * @see Flexihash_Hasher::hash()

   */

  public function hash($string)

  {

    return substr(md5($string), 0, 8); // 8 hexits = 32bit

    // 4 bytes of binary md5 data could also be used, but

    // performance seems to be the same.

  }

}

/**

 * An exception thrown by Flexihash.

 *

 * @author Paul Annesley

 * @package Flexihash

 * @licence http://www.opensource.org/licenses/mit-license.php

 */

class Flexihash_Exception extends Exception

{

}

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