The half-adder form and early branch condition resolution

The authors present efficient methods to determine the four usual branch conditions for a sum or difference, before the result of the addition or subtraction is available. The methods lead to the design of an early branch resolver which integrates well with a regular adder/subtracter, adding only a small amount of circuitry and almost no delay. The methods exploit the properties of half-adder form. Sums in half-adder form can be computed vary quickly (with the delay of a half adder), yet they have enough structure so that many of the properties of the final sum can be easily detected. The reduced latency for evaluating branch conditions means that an addition or subtraction and a dependent conditional instruction can execute in the same cycle with a consequent increase in instruction-level parallelism, and improved performance for both single-issue and superscalar processors.