basic_verilog/Advanced Synthesis Cookbook/ethernet_fec/fec_rot_13.v

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//
// 32 bit CRC of 13 data bits (forward - LSB first)
// polynomial : 00a00805 
//    x^23 + x^21 + x^11 + x^2 + x^0
//
//        CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC DDDDDDDDDDDDD 
//        00000000001111111111222222222233 0000000000111 
//        01234567890123456789012345678901 0123456789012 
// C00  = ...................#........#.#. ............. 
// C01  = ....................#........#.# ............. 
// C02  = ...................#.#......#... ............. 
// C03  = ....................#.#......#.. ............. 
// C04  = .....................#.#......#. ............. 
// C05  = ......................#.#......# ............. 
// C06  = .......................#.#...... ............. 
// C07  = ........................#.#..... ............. 
// C08  = .........................#.#.... ............. 
// C09  = ..........................#.#... ............. 
// C10  = ...........................#.#.. ............. 
// C11  = ...................#............ ............. 
// C12  = ....................#........... ............. 
// C13  = #....................#.......... ............. 
// C14  = .#....................#......... ............. 
// C15  = ..#....................#........ ............. 
// C16  = ...#....................#....... ............. 
// C17  = ....#....................#...... ............. 
// C18  = .....#....................#..... ............. 
// C19  = ......#....................#.... ............. 
// C20  = .......#....................#... ............. 
// C21  = ........#..........#........###. ............. 
// C22  = .........#..........#........### ............. 
// C23  = ..........#........#.#......#..# ............. 
// C24  = ...........#........#.#......#.. ............. 
// C25  = ............#........#.#......#. ............. 
// C26  = .............#........#.#......# ............. 
// C27  = ..............#........#.#...... ............. 
// C28  = ...............#........#.#..... ............. 
// C29  = ................#........#.#.... ............. 
// C30  = .................#........#.#... ............. 
// C31  = ..................#........#.#.. ............. 
//
// Number of XORs used is 32
// Maximum XOR input count is 5
//   Best possible depth in 4 LUTs = 2
//   Best possible depth in 5 LUTs = 1
//   Best possible depth in 6 LUTs = 1
// Total XOR inputs 88
//

module fec_rot_13 (
    input [31:0] c,
    output [31:0] co
);

assign co[0] =
    c[19] ^ c[28] ^ c[30];

assign co[1] =
    c[20] ^ c[29] ^ c[31];

assign co[2] =
    c[19] ^ c[21] ^ c[28];

assign co[3] =
    c[20] ^ c[22] ^ c[29];

assign co[4] =
    c[21] ^ c[23] ^ c[30];

assign co[5] =
    c[22] ^ c[24] ^ c[31];

assign co[6] =
    c[23] ^ c[25];

assign co[7] =
    c[24] ^ c[26];

assign co[8] =
    c[25] ^ c[27];

assign co[9] =
    c[26] ^ c[28];

assign co[10] =
    c[27] ^ c[29];

assign co[11] =
    c[19];

assign co[12] =
    c[20];

assign co[13] =
    c[0] ^ c[21];

assign co[14] =
    c[1] ^ c[22];

assign co[15] =
    c[2] ^ c[23];

assign co[16] =
    c[3] ^ c[24];

assign co[17] =
    c[4] ^ c[25];

assign co[18] =
    c[5] ^ c[26];

assign co[19] =
    c[6] ^ c[27];

assign co[20] =
    c[7] ^ c[28];

assign co[21] =
    c[8] ^ c[19] ^ c[28] ^ c[29] ^ c[30];

assign co[22] =
    c[9] ^ c[20] ^ c[29] ^ c[30] ^ c[31];

assign co[23] =
    c[10] ^ c[19] ^ c[21] ^ c[28] ^ c[31];

assign co[24] =
    c[11] ^ c[20] ^ c[22] ^ c[29];

assign co[25] =
    c[12] ^ c[21] ^ c[23] ^ c[30];

assign co[26] =
    c[13] ^ c[22] ^ c[24] ^ c[31];

assign co[27] =
    c[14] ^ c[23] ^ c[25];

assign co[28] =
    c[15] ^ c[24] ^ c[26];

assign co[29] =
    c[16] ^ c[25] ^ c[27];

assign co[30] =
    c[17] ^ c[26] ^ c[28];

assign co[31] =
    c[18] ^ c[27] ^ c[29];

endmodule