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 [4:0] sum5 = {1'b0, a} + {1'b0, ~b} + 5'b00001; 
    assign diff = sum5[3:0];
    assign bout = ~sum5[4]; 

endmodule