69. Binary Subtractor

How do you plan to solve it?

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

    assign {cout, diff} = {1'b0, a} + ~{1'b1, b} + 1;
    assign bout = ~cout;
endmodule