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
);
    wire [4:0] diff5 = {1'b0,a} + {1'b0,~b} + 1;
    assign bout = ~diff5[4];
    assign diff = diff5[3:0];
endmodule