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