PHP基于md5生成短HASH的代码

/*********
* CHash provides users with a fairly strong but short hash for identification
* Based on MD5
**********/
class stdHash{
    var $hashIn = '';
    function __construct($hashIn=''){
        $this->hashIn = $hashIn;
    }
    function hash($string){
        $cherryTable = Array('0'=>0,'1'=>1,'2'=>2,'3'=>3,'4'=>4,'5'=>5,'6'=>6,'7'=>7,'8'=>8,'9'=>9,'A'=>10,'B'=>11,'C'=>12,'D'=>13,'E'=>14,'F'=>15);
        $md = md5($string.$this->hashIn);$m="";
        for($i=0;$i<16;$i++){
            $m.=chr($cherryTable[$md[$i*2]]*16 + $cherryTable[$md[$i*2+1]]);
        }
        return preg_replace('~[N=]~','',str_rot13(base64_encode($m)));
    }
}