71. Arithmetic Logic Unit

How do you plan to solve it?

/*Write your code here*/
module alu4(input [3:0]a ,input[3:0]b , input [2:0]op , output reg [3:0]y , output reg cf);
always@(*) begin
case(op)
    3'b000 : {cf, y} = a + b;
    3'b001 : {cf, y} = a + (~b) + 1;
    3'b010 : begin y = a & b;  cf=0; end
    3'b011 : begin y = a | b;  cf=0; end
    3'b100 : begin y = a ^ b;  cf=0; end
    default : begin y=4'b0; cf=0; end
endcase
end
endmodule