public function writeString(&$string)
    {
        $len = strlen($string);
        if(!$len){
            $this->writeInteger(0x01);
            return $this;
        }

        $ref = array_key_exists($string, $this->_referenceStrings) 
             ? $this->_referenceStrings[$string] 
             : false;
        if ($ref === false){
            $this->_referenceStrings[$string] = count($this->_referenceStrings);
            $this->writeBinaryString($string);
        } else {
            $ref <<= 1;
            $this->writeInteger($ref);
        }

        return $this;
    }