69. Binary Subtractor

How do you plan to solve it?

/*Write your code here*/
module sub4_2c (
    input [3:0] a,
    input [3:0] b,
    output bout,
    output [3:0] diff
);

    wire cout;

    assign {cout, diff} = a + (~b) + 1;
    assign bout = cout;

endmodule