Still doesn't make sense. Yes, things like Brent-Kung adders are O(2^N) in the bit length of the input, but the adders are pipelined. You only avoid the transition current in the stateless logic if all the addition operations are of the same values every clock cycle. But obviously you can't do that if you want to compute something. I still don't buy it. On anything bigger than a 6502, there is no way this would be measurable. None whatsoever.