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'b0000;
                   cf = 0;
            end
    endcase
 end
endmodule