Floating-point fused multiply-add with reduced latency

Abstract

We propose an architecture for the computation of the floating-point multiply-add-fused (MAF) operation A+ (B /spl times/ C). This architecture is based on the combined addition and rounding (using a dual adder) and on the anticipation of the normalization step before the addition. Because the normalization is performed before the addition, it is not possible to overlap the leading-zero-anticipator with the adder. Consequently, to avoid the increase in delay we modify the design of the LZA so that the leading bits of its output are produced first and can be used to begin the normalization. Moreover, parts of the addition are also anticipated. We have estimated the delay of the resulting architecture for double-precision format, considering the load introduced by long connections, and estimate a reduction of about 15% to 20% with respect to traditional implementations of the floating-point MAF unit.