Design of ALU ALU forms one of the important block of a digital computer. It is a multi-operation, combinational circuit. Number of operations supported depend on the complexity of its design. It takes two numbers of n-bit wide as input, performs an operation depending on the function select inputs and produces the output Fn, It also has carry-in input to provide additional functionality and carry-out line which can be part of the result or can act as input to the next stage when the functionality is extended to accommodate numbers with more number of bits. If an ALU has k function select lines, then it will have 2k operations. Figure-1 shows the block diagram of an ALU. Modular design technique can be