function _getExtraParam(bytes _extraData) 
        private 
        pure
        returns(address addr, uint64 f, uint256 protoId) 
    {
        assembly { addr := mload(add(_extraData, 20)) } 
        f = uint64(_extraData[20]);
        protoId = uint256(_extraData[21]) * 256 + uint256(_extraData[22]);
    }