167 MHz radix-8 divide and square root using overlapped radix-2 stages

Abstract

UltraSPARC's IEEE-754 compliant floating point divide and square root implementation is presented. Three overlapping stages of SRT radix-2 quotient selection logic enable an effective radix-8 calculation at 167 MHz while only a single radix-2 quotient selection logic delay is seen in the critical path. Speculative partial remainder and quotient calculation in the main datapath also improves cycle time. The quotient selection logic is slightly modified to prevent the formation of a negative partial remainder for exact results. This saves latency and hardware as the partial remainder no longer needs to be restored before calculating the sticky bit for rounding.<>