Abstract: An arithmetic logic unit for a microprocessor is shown and described for use in a 24-bit data path where the ALU includes three separate ALU portions, one for each byte of the data path, and three separate control signals, one for each portion of the ALU. The ALU provides a variety of arithmetic and logic functions for application to 24-bit operands, but also includes a capability of manipulating such operands in accordance with sign extended opcodes without actually physically executing a sign extend operation within the microprocessor. In this manner, the ALU executes the necessary logic functions to provide the same ultimate result as sign bit extension, but does not require a separate sign bit extension step within the microprocessor to convert signed byte operand into a signed word operand.