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 reg [3:0] diff, 
    output reg bout
);

always @(*) begin
    bout=0;
if (a<b) begin
    bout = 1;
end

diff = a+ (~b+1);

end
endmodule