> Your code is wrong in many places. In short, exceptional situation should leave your object in correct state.
Yeah, I know, but I wanted to get the overflow flag check working first and worry about transactional integrity later. The way I was thinking of doing it is storing the result in a temporary, which gets the checks, then having scope(success) commit it to the _payload. But I just haven't gotten around to it yet - it's just a starting point, not a finished product.
