Delay-Optimum Adder Circuits with Linear Size

Abstract

We present efficient circuits for the addition of binary numbers. We assume that we are given arrival times for all input bits and optimize the delay of the circuits, i.e.\ the time when the last output bit is computed. This contains the classical optimization of depth as a special case where all arrival times are $0$. In this model, we present, among other results, the fastest adder circuits of sub-quadratic size and the fastest adder circuits of linear size. In particular, for adding two $n$-numbers we get a circuits with linear size and delay $\log_2W+3\log_2\log_2n+4\log_2\log_2\log_2n +const$ where $\log_2W$ is a lower bound for the delay of any adder circuit (no matter what size it has).