protected int __offset(int vtable_offset){
  int vtable=bb_pos - bb.getInt(bb_pos);
  return vtable_offset < bb.getShort(vtable) ? bb.getShort(vtable + vtable_offset) : 0;
}

protected int __offset ( int vtable_offset ) { int vtable = bb_pos - bb . getInt ( bb_pos ) ; return vtable_offset < bb . getShort ( vtable ) ? bb . getShort ( vtable + vtable_offset ) : 0 ; }
look up a field in the vtable .
