69. Binary Subtractor

How do you plan to solve it?

module sub4_2c(
    input [3:0] a,
    input [3:0] b,
    output [3:0] diff,
    output bout
);

    assign diff = a + (~b + 1);
    assign bout = (a < b) ? 1'b1 : 1'b0;

endmodule