71. Arithmetic Logic Unit

How do you plan to solve it?

/*Write your code here*/
module alu4(
    input [3:0]a,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;
    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'd0;
        cf= 0;
    end
    endcase
end
endmodule