PAPA - packed arithmetic on a prefix adder for multimedia applications

This paper introduces PAPA: packed arithmetic on a prefix adder, a new approach to parallel prefix adder design that supports a wide variety of packed arithmetic computations, including packed add and subtract with saturation, packed rounded average, and packed absolute difference. The approach consists of altering the prefix adder cell logic equations to take advantage of a previously unused "don\´t care" state. The principle of logical effort is employed to assess the delay of the new adder architecture by establishing the extra effort needed to select and drive the appropriate carry signal to the requisite sum sub-word. This adder will find applications in video processors and other multimedia-orientated processor chips that implement packed arithmetic operations.