simhash的原理和php实现

1 simhash的原理，比较详细的参考链接：http://my.oschina.net/leejun2005/blog/150086
2 simhash的php实现（如下）。主要用到了php的类库gmp
3 ps：oshchina代码编辑器真心难用，大家将就一下。。以后改好哈。希望能改进！！
4 因为工作原因用php重写了simhash算法

<?php

/
@author [email protected]
/
class Simhash
{

public $m_hash = null;
public $hashbits = null;

//构造函数
public function __construct($tokens=array(), $hashbits=128)
{
    $this->m_hashbits = $hashbits;
    $this->m_hash = $this->simhash($tokens);
}

//to string
public function __toString()
{
    return strval($this->m_hash);
}

//返回hash值
public function simhash($tokens)
{
    if(!is_array($tokens))
    {

        throw new Exception("tokens should be array");
    }

    $v = array_fill(0,$this->m_hashbits,0);
    foreach($tokens as $x)
    {
        $x = $this->stringHash($x);
        for($i=0;$i<$this->m_hashbits;$i++)
        {
            $bitmask = gmp_init(1);
            gmp_setbit($bitmask, $i);
            $bitmask = gmp_sub($bitmask,1);
            if (gmp_strval(gmp_and($x,$bitmask)) != "0")
            {
                $v[$i] += 1;
            }
            else
            {
                $v[$i] -= 1;
            }
        }
    }
    $sum = 0;
    for($i=0;$i<$this->m_hashbits;$i++)
    {
        if ($v[$i] >= 0)
        {
            $num = gmp_init(1);
            gmp_setbit($num, $i);
            $num = gmp_sub($num,1);
            $sum = gmp_add($sum,$num);
        }
    }
    return gmp_strval($sum);
}

//求海明距离
public function hammingDistance($other)
{
    $a = gmp_init($this->m_hash);
    $b = gmp_init($other->m_hash);

    $c = gmp_init(1);
    gmp_setbit($c, $this->m_hashbits);
    $c = gmp_sub($c,2);
    $x = gmp_and(gmp_xor($a,$b),$c);
    $tot = 0;
    while(gmp_strval($x))
    {
        $tot += 1;
        $x = gmp_and($x,gmp_sub($x,1));
    }
    return $tot;
}

//求相似度
public function similarity ($other)
{
    $a = floatval($this->m_hash);
    $b = floatval($other->m_hash);
    if($a > $b)
    {
        return $b/$a;
    }
    else
    {
        return $a/$b;
    }
}

public function stringHash($source)
{
    if(empty($source))
    {
        return 0;
    }
    else
    {
        $x = ord($source[0]) << 7;

        $m = 1000003;

        $mask = gmp_sub(gmp_pow("2", $this->m_hashbits),1);
        $len = strlen($source);

        for($i=0;$i<$len;$i++)
        {
            $x = gmp_and(gmp_xor(gmp_mul($x,$m),ord($source[$i])),$mask);
        }
        $x = gmp_xor($x,$len);
        if(intval(gmp_strval($x)) == -1)
        {
            $x = -2;
        }
        return $x;
    }
}

}

$s = 'This is a test string for testing';

$hash1 = new Simhash(explode(” “,$s));

$s = 'This is a test string for testing also';

$hash2 = new Simhash(explode(” “,$s));

$s = 'nai nai ge xiong cao';
$hash3 = new Simhash(explode(” “,$s));

var_dump($hash1->hammingDistance($hash2) , " " , $hash1->similarity($hash2));
var_dump($hash1->hammingDistance($hash3) , " " , $hash1->similarity($hash3));