Combined decoder/adder circuit which provides improved access speed to a cache

摘要

The present invention is directed toward an combined decoder/adder circuit which provides faster access to a cache in a microprocessor than implementations which include an adder circuit which is followed by a decoder circuit. By decoding the upper order bits of a first operand and then rotating the upper order bits of the first operand by the upper order bits of a second operand, followed by an additional shift by one which is enabled by a carry generator the overall speed of the critical path is greatly increased. Accordingly, the time needed for generating an effective address (EA) and therefore accessing the cache is significantly decreased. The present invention has significant utility in microprocessors in which the word line decode is the critical path.