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
        cf = 0;
        case(op) 
        3'b000 : {cf,y} = a+b;
        3'b001 :  begin
            y = a+ (~b)+1;
            cf = a<b?1:0;
        end
        3'b010 : y = a&b;
        3'b011 : y = a|b;
        3'b100 : y = a^b;

        default : y = 4'b0000;
        endcase
    end
endmodule