protected function subtractBinary($left, $right) {
        $len    = max(strlen($left), strlen($right));
        $left   = str_pad($left, $len, chr(0), STR_PAD_LEFT);
        $right  = str_pad($right, $len, chr(0), STR_PAD_LEFT);
        $right  = $this->compliment($right);
        $result = $this->addBinary($left, $right);
        if (strlen($result) > $len) {
            // Positive Result
            $carry  = substr($result, 0, -1 * $len);
            $result = substr($result, strlen($carry));
            return array(
                '',
                $this->addBinary($result, $carry)
            );
        }
        return array('-', $this->compliment($result));
    }