1. Introduction
There are many ways of formulating the process of binary addition. Each different way provides different insight and thus suggests different implementations. Examples are Weinberger & Smith's carry-lookahead adder [Wein58], Nadler's pyramid adder [Nad156], Sklansky's conditional sum adder [Skla60], Bedrij's carry-select adder [Bedr62], and Ladner & Fischer's prefix adder [Ladn80]. For a general introduction see [Omon94]. The prefix formulation is particularly attractive because it is easily expressed and suggests very efficient implementations, ie. adders based on this formulation can be attractively fast and compact when implemented in VLSI.