本篇文章主要介绍php哈希算法的相关技巧，感兴趣的朋友参考下，希望对大家有所帮助。
本文实例讲述了php实现的一致性哈希算法。分享给大家供大家参考，具体如下：
<?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 '$target' 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 '$target' does not exist."); } foreach ($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('no targets exist'); 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('invalid count requested'); // 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 $results; } public function __tostring() { return sprintf( '%s{targets:[%s]}', get_class($this), implode(',', $this->getalltargets()) ); } // ---------------------------------------- // private methods /** * sorts the internal mapping (positions to targets) by position */ private function _sortpositiontargets() { // sort by key (position) if not already if (!$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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以上就是php哈希算法的相关技巧的详细内容。