PHP中实现Bloom Filter算法_php技巧

one_num = 8;  //默认32m*1  $this->space_group_num = $space_group_num;  $this->hash_space_assoc = array();  //分配空间  for($i=0; $ispace_group_num; $i++){   $this->hash_space_assoc[$i] = str_repeat($binary, $max_length);  }  $this->pow_array = array(   0 => 1,   1 => 2,   2 => 4,   3 => 8,   4 => 16,   5 => 32,   6 => 64,   7 => 128,  );  $this->chr_array = array();  $this->ord_array = array();  for($i=0; $ichr_array[$i] = $chr;   $this->ord_array[$chr] = $i;  }  $this->hash_func_pos = array(   0 => array(0, 7, 1),   1 => array(7, 7, 1),   2 => array(14, 7, 1),   3 => array(21, 7, 1),   4 => array(28, 7, 1),   5 => array(33, 7, 1),   6 => array(17, 7, 1),  );  $this->write_num = 0;  $this->ext_num = 0;  if(!$hash_func_num){   $this->hash_func_num = count($this->hash_func_pos);  }  else{   $this->hash_func_num = $hash_func_num;  } } function add($key) {  $hash_bit_set_num = 0;// 离散key  $hash_basic = sha1($key);//  截取前4位,然后十六进制转换为十进制  $hash_space = hexdec(substr($hash_basic, 0, 4));//  取模  $hash_space = $hash_space % $this->space_group_num;  for($hash_i=0; $hash_ihash_func_num; $hash_i++){   $hash = hexdec(substr($hash_basic, $this->hash_func_pos[$hash_i][0], $this->hash_func_pos[$hash_i][1]));   $bit_pos = $hash >> 3;   $max = $this->ord_array[$this->hash_space_assoc[$hash_space][$bit_pos]];   $num = $hash - $bit_pos * $this->one_num;   $bit_pos_value = ($max >> $num) & 0x01;   if(!$bit_pos_value){    $max = $max | $this->pow_array[$num];    $this->hash_space_assoc[$hash_space][$bit_pos] = $this->chr_array[$max];    $this->write_num++;   }   else{    $hash_bit_set_num++;   }  }  if($hash_bit_set_num == $this->hash_func_num){   $this->ext_num++;   return true;  }  return false; } function get_stat() {  return array(   'ext_num' => $this->ext_num,   'write_num' => $this->write_num,  ); }}<strong style="color:transparent">本文来源gao@daima#com搞(%代@#码@网&</strong><strong>搞gaodaima代码</strong>//test//取6个哈希值，目前是最多7个$hash_func_num = 6;//分配1个存储空间，每个空间为32M，理论上是空间越大误判率越低，注意php.ini中可使用的内存限制$space_group_num = 1;$bf = new bloom_filter($hash_func_num, $space_group_num);$list = array( 'http://test/1', 'http://test/2', 'http://test/3', 'http://test/4', 'http://test/5', 'http://test/6', 'http://test/1', 'http://test/2',);foreach($list as $k => $v){ if($bf->add($v)){  echo $v, "\n"; }}print_r($bf->get_stat());