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: begin
                {cf, y} = a + b;
            end
            3'b001: begin
                {cf, y} = a+~b+1'b1;
            end
            3'b010: begin
                y = a & b;
                cf = 1'b0;
            end
            3'b011: begin
                y = a | b;
                cf = 1'b0;
            end
            3'b100: begin
                y = a ^ b;
                cf = 1'b0;
            end
            default : begin
                y = 4'b0000;
                cf = 1'b0;
            end
        endcase
    end

endmodule