PHP中实现Bloom Filter算法

            
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,
  );
}
}
//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());
            
            
您可能感兴趣的文章:

布隆过滤器(Bloom Filter)的Java实现方法