`timescale 1ns / 1ps
`include "cam_params.svh"

module noise_mask_grouped #(
    parameter int HASH_BITS      = `HASH_BITS,
    parameter int NOISE_BITS     = 8,
    parameter int NOISE_RATE_NUM = 1,
    parameter int NOISE_RATE_DEN = 100
) (
    input  logic [127:0]          random_i,
    output logic [HASH_BITS-1:0]  mask_o
);
    localparam int GROUP_BITS       = HASH_BITS / NOISE_BITS;
    localparam int BIT_INDEX_BITS   = 6;
    localparam int SAMPLE_BITS      = 8;
    localparam int GROUP_RAND_BITS  = BIT_INDEX_BITS + SAMPLE_BITS;
    localparam int SAMPLE_RANGE     = 1 << SAMPLE_BITS;
    localparam int THRESHOLD        = (NOISE_RATE_NUM * SAMPLE_RANGE) / NOISE_RATE_DEN;

    initial begin
        if (NOISE_BITS <= 0) $fatal(1, "NOISE_BITS must be > 0");
        if (HASH_BITS % NOISE_BITS != 0) $fatal(1, "HASH_BITS must be divisible by NOISE_BITS");
        if (GROUP_BITS != 64) $fatal(1, "GROUP_BITS must be 64 for 6-bit grouped noise");
        if (NOISE_BITS * GROUP_RAND_BITS > 128) $fatal(1, "NOISE_BITS consumes more than 128 random bits");
        if (NOISE_RATE_DEN <= 0) $fatal(1, "NOISE_RATE_DEN must be > 0");
        if (NOISE_RATE_NUM < 0 || NOISE_RATE_NUM > NOISE_RATE_DEN) $fatal(1, "NOISE_RATE_NUM out of range");
    end

    always_comb begin
        mask_o = '0;
        for (int i = 0; i < NOISE_BITS; i++) begin
            if (random_i[i * GROUP_RAND_BITS + BIT_INDEX_BITS +: SAMPLE_BITS] < THRESHOLD) begin
                mask_o[i * GROUP_BITS + random_i[i * GROUP_RAND_BITS +: BIT_INDEX_BITS]] = 1'b1;
            end
        end
    end
endmodule