/* inc4fexb: by karttu, Jan 2 2005.
             Increment the four-digit factorial expansion
             specified in one-bit register in_f0 (the least
             significant digit) and the next thee digits
             in three binary registers (in_f1 - in_f3)
             and give the results in out_fo - out_f3.

             Note that in_f0 can be used as a kind
             of "incrementation enable" signal, because
             the incrementing is carried only when
             it is 1.

             This differs from inc4fex in that here
             we don't use "one hot" encoding, but
             instead each digit is presented with
             the ordinary binary encoding.
 */

module inc4fexb(input in_f0,
                input [1:0] in_f1, // 0-2 (2b'00, 2b'01 or 2b'10)
                input [1:0] in_f2, // 0-3 (2b'00, 2b'01, 2b'10 or 2b'11)
                input [2:0] in_f3, // 0-4 (3b'000 - 3b'100)
                output out_f0,
                output [1:0] out_f1,
                output [1:0] out_f2,
                output [2:0] out_f3);

assign out_f0 = ~in_f0;

// How to do this with (nested) generate loop(s) ?

assign out_f1 = (in_f0 ? (2 == in_f1 ? 0 : in_f1+1) : in_f1);
assign out_f2 = ((in_f0 && (2 == in_f1)) ? in_f2+1 : in_f2);
assign out_f3 = ((in_f0 && (2 == in_f1) && (3 == in_f2))
                  ? (4 == in_f3 ? 0 : in_f3+1)
                  : in_f3);


endmodule