A Formulation of Fast Carry Chains Suitable for Efficient Implementation with Majority Elements

Abstract

Carry computation is a most important notion in computer arithmetic, because it dictates the speed of addition, which is in turn vital to high-speed computation, both as a directly used primitive and as a building block for synthesizing other operations. The theory of fast addition is well-established, but from time to time, changes in technology necessitate a reassessment of strategies for carry network implementation, even though the logical functions to be realized remain the same. We study the implications of the availability of simple, fast, and power-efficient majority gates (in technologies such as quantum-dot cellular automata, single-electron tunneling, tunneling phase logic, magnetic tunnel junction, and nanoscale bar magnets) to the design of carry networks, offering a reformulation of the carry recurrence that allows for building carry networks exclusively out of fully utilized majority elements. We compare our novel implementations based on 3-input majority elements to prior proposals based on these elements, demonstrating advantages in both speed and circuit complexity.