hamming

module hamming_gen #(
    parameter NUM_PARITY = 3
) (
    input  logic [  NUM_DATA - 1 : 0] data,
    output logic [NUM_PARITY - 1 : 0] parity
);
    localparam NUM_DATA = 2 ** NUM_PARITY - NUM_PARITY - 1;
    localparam NUM_TOTAL = 2 ** NUM_PARITY - 1;

    function parity_covers(input integer p, input integer d);
        integer i;
        integer j = 0;
        for (i = 1; i <= NUM_TOTAL && j < d; i++)
            if (i != (i & ~(i - 1))) /* Data bit */
                j++;
        return ((i - 1) >> (p - 1)) & 1;
    endfunction

    function integer foo(input integer d);
        integer i;
        integer j = 0;
        for (i = 1; i <= NUM_TOTAL && j < d; i++)
            if (i != (i & ~(i - 1))) /* Data bit */
                j++;
        return i - 1;
    endfunction

    generate
        genvar i, j;
        for (i = 0; i < NUM_PARITY; i++) begin
            for (j = 0; j < NUM_DATA; j++) begin
                if (parity_covers(i + 1, j + 1)) begin
                    assign parity[i] = ^data[j];
                end
                /*if ((j & ~(j - 1)) != j) begin
                    assign parity[i] = ^data[j - (j & ~(j - 1))];
                end*/
            end
        end
    endgenerate

        initial begin
        integer i, j;

        for (i = 1; i <= NUM_DATA; i++)
            $display("%d -> %d", i, foo(i));

        for (i = 1; i <= NUM_PARITY; i++)
            for (j = 1; j <= NUM_DATA; j++)
                $display("parity_covers(%d, %d): %d", i, j, parity_covers(i, j));
                /*$display("parity: %d\n  data: %d\n total: %d",
            NUM_PARITY, NUM_DATA, NUM_PARITY + NUM_DATA);*/
        end
endmodule