Leading-zero anticipator (LZA) in the IBM RISC System/6000 floating-point execution unit

Abstract

This paper presents a novel technique used in the multiply-add-fused (MAF) unit of the IBM RISC System/6000* (RS/6000) processor for normalizing the floating-point results. Unlike the conventional procedures applied thus far, the so-called leading-zero anticipator (LZA) of the RS/6000 carries out processing of the leading zeros and ones in parallel with floating-point addition. Therefore, the new circuitry reduces the total latency of the MAF unit by enabling the normalization and addition to take place in a single cycle.