EARLY SCISM ALU STATUS DETERMINATION APPARATUS

摘要

A status determination apparatus, includes a three-to-one arithmetic logic unit (ALU), for predicting the status of the ALU operations related to the carries incorporated in the ALU which is designed to execute a second instruction of an interlock instruction pair in parallel whether or not the second instruction is independent or dependent on a result of the operation of the first instruction. An apparatus is developed (Figs. 2-3) for generating carries (C0, C1) due to the second instruction of the interlock instruction pair when executing all combinations of logical and aritthmetic pair. A critical path for calculating the carries ( lambda ) is first presented. Next, the expression for generating the carries ( lambda ) is used to derive a fast implementation (Figs. 4-5) for generating an overflow (OF). Additionally, an implementation scheme is developed for predicting result equal to zero (Fig. 6).