Wouldn’t that produce 2^n possible results to choose from, where n is the number of chunks? That seems like a lot of additional (he-he) instructions executed.
But for a single addition you will also not save any time because you still need to do the select in series. The whole point of the radix 2^51 trick is that you can defer the normalization over several additions, but in order to do that your carry needs to be more than a single bit.
