/* fex4perm: by karttu, Jan 2 2005.
             Output the permutation corresponding
             to factorial expansion that is given
             in f0 - f3. The result is output
             in out_d0 - out_d4, i.e. five digits 0-4
             given in the order specified by "A060118 algorithm".

             Should be used together with the module inc4fexb.v

 */

module fex4perm(input f0,
                input [1:0] f1, // 0-2 (2b'00, 2b'01 or 2b'10)
                input [1:0] f2, // 0-3 (2b'00, 2b'01, 2b'10 or 2b'11)
                input [2:0] f3, // 0-4 (3b'000 - 3b'100)
                output [2:0] d0,
                output [2:0] d1,
                output [2:0] d2,
                output [2:0] d3,
                output [2:0] d4);

parameter w = 2;

parameter [w:0] lev0_0 = 3'b000;
parameter [w:0] lev0_1 = 3'b001;
parameter [w:0] lev0_2 = 3'b010;
parameter [w:0] lev0_3 = 3'b011;
parameter [w:0] lev0_4 = 3'b100;

wire [w:0] lev1_0 = (0 == f0 ? lev0_0 : lev0_1);
wire [w:0] lev1_1 = (0 == f0 ? lev0_1 : lev0_0);

wire [w:0] lev2_0 = (2 == f1 ? lev0_2 : lev1_0);
wire [w:0] lev2_1 = (1 == f1 ? lev0_2 : lev1_1);
wire [w:0] lev2_2 = (2 == f1 ? lev1_0 : (1 == f1 ? lev1_1 : lev0_2));

wire [w:0] lev3_0 = (3 == f2 ? lev0_3 : lev2_0);
wire [w:0] lev3_1 = (2 == f2 ? lev0_3 : lev2_1);
wire [w:0] lev3_2 = (1 == f2 ? lev0_3 : lev2_2);
wire [w:0] lev3_3 = (3 == f2 ? lev2_0 : (2 == f2 ? lev2_1 : (1 == f2 ? lev2_2 : lev0_3)));

wire [w:0] lev4_0 = (4 == f3 ? lev0_4 : lev3_0);
wire [w:0] lev4_1 = (3 == f3 ? lev0_4 : lev3_1);
wire [w:0] lev4_2 = (2 == f3 ? lev0_4 : lev3_2);
wire [w:0] lev4_3 = (1 == f3 ? lev0_4 : lev3_3);
wire [w:0] lev4_4 = (4 == f3 ? lev3_0  : (3 == f3 ? lev3_1 : (2 == f3 ? lev3_2 : (1 == f3 ? lev3_3 : lev0_4))));

assign d0 = lev4_0;
assign d1 = lev4_1;
assign d2 = lev4_2;
assign d3 = lev4_3;
assign d4 = lev4_4;

endmodule