A high-performance 3-1 interlock collapsing ALU, i.e., an ALU that allows the execution of most execution interlocks in a single machine cycle, is presented. We focus on reducing the Boolean equations describing the device and the incorporation of new mechanisms in the interlock collapsing ALU design. In particular, we focus on the reduction of the critical path, regarding delay, for the interlock collapsing ALU implementation. It is shown that the delay associated with the implementation of the proposed device, in terms of logic stages, assuming a commonly available CMOS technology, is equivalent to the number of logic stages required for the implementation of a 3-1 binary adder. The resulting implementation demonstrates that the proposed 3-1 interlock collapsing ALU can be designed to outperform existing schemes for interlock collapsing ALU's by a factor of at least two. Finally, it is suggested that the proposed device can be used in the implementation of multiple instruction issuing machines, allowing the issuance and execution of interlocks in parallel and in a single machine cycle with no cycle time increases.>

A device capable of executing interlocked fixed point arithmetic logic unit (ALU) instructions in parallel with other instructions causing the execution interlock is presented. The device incorporates the design of a 3-1 ALU and can execute two's complement, unsigned binary, and binary logical operations. It is shown that status for ALU operations using a 3-1 ALU can be determined in a parallel fashion, resulting in the compliance of the proposed device with predetermined architectural behavior of single instruction execution. The device requires no more logic stages than does a 3-1 binary adder using a carry-save adder (CSA) followed by a carry-lookahead adder (CLA) design. Design considerations using a commonly available CMOS technology are also reported, indicating that the device will not increase the machine cycle of an implementation. It is suggested that the device can maintain full architectural compatibility.>