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
        y  = 4'b0000;
        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;
        endcase
    end
endmodule