ARITHMETIC PROCESSOR AND MICROPROCESSOR

PROBLEM TO BE SOLVED: To provide an arithmetic processor and microprocessor which enalbe a user to define instructions and can execute the user-defined instructions with high throughput. SOLUTION: This arithmetic processor(ALU) 20 of the microprocessor includes a memory 22 which has at least part of an instruction space defined as a user-defined instruction area and previously stores instruction codes belonging to the user-defined instruction area and process results corresponding to combinations of various operand codes by regarding the combinations of the respective instruction codes and operand data as addresses. A PLD (programmable logic device) may be used instead of the memory 22. The arithmetic processor 20 may includes an ALU consisting of connection logic for executing instructions that belongs to an area other than the user-defined instruction area and a multiplexer which selects one of the memory 22 and ALU by receiving an instruction code and places it in operation.