docs: protected final long getIValue(int off){
      switch(_valsz){
        case 1: return _mem[off+ _ridsz]&0xFF;
        case 2: return UDP.get2(_mem, off + _ridsz);
        case 4: return UDP.get4(_mem, off + _ridsz);
        case 8: return UDP.get8(_mem, off + _ridsz);
        default: throw H2O.unimpl();
     }
    }