FallenSigh
717a9929b6
- Replace / and % operators in comp_decomp_sync with Barrett multiply-by-reciprocal (dividend * 5039 >> 24) + correction step. Eliminates ~100 CARRY4 divider chain. - Add include_dirs for sources_1 fileset so Windows Vivado synthesis finds defines.vh. - Change CLK_PERIOD from 10.0 (100MHz) to 40.0 (50MHz) to reflect actual target.
97 lines
4.1 KiB
Verilog
97 lines
4.1 KiB
Verilog
// comp_decomp_sync.v - ML-KEM coefficient compression/decompression
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//
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// Streaming: one coefficient per cycle through pipeline_reg.
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// mode=0: compress - round((2^d * x) / Q) mod 2^d
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// mode=1: decompress - round((Q * x) / 2^d) mod Q
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// Uses round-half-up (round(2.5)=3, round(3.5)=4).
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// Integer arithmetic:
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// compress: (x * 2^d + Q/2) / Q, lower d bits as result
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// decompress: (x * Q + 2^(d-1)) / 2^d, result mod Q
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//
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// Division by Q=3329 replaced with Barrett multiplication + correction:
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// floor(x / Q) ≈ (x * 5039) >> 24 (5039 = floor(2^24 / 3329))
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// Correction: if x - q_approx * Q >= Q, add 1 to quotient.
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// Q*5039 = 16,774,831 < 2^24, so Barrett may under-estimate by 1.
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// Q = 3329 = 2048+512+256+1, so q*Q uses 3 shifts + add (no 2nd multiplier).
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`include "sync_rtl/common/defines.vh"
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(* use_dsp = "no" *)
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module comp_decomp_sync (
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input clk,
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input rst_n,
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input [11:0] coeff_in,
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input [4:0] d,
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input mode, // 0=compress, 1=decompress
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input valid_i,
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output ready_o,
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output [11:0] coeff_out,
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output valid_o,
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input ready_i
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);
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wire [11:0] two_pow_d = 12'd1 << d;
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// product: 12b*12b = max 2048*3328 = 6,815,744 → 23b, pad to 24b
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wire [23:0] product = mode ? {12'b0, coeff_in} * {12'b0, 12'(`Q)}
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: {12'b0, coeff_in} * {12'b0, two_pow_d};
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wire [11:0] round_off = mode ? (two_pow_d >> 1) : 12'd1664;
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wire [23:0] dividend = product + {12'b0, round_off};
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// ===========================================================
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// Barrett: floor(x / Q) ≈ (x * 5039) >> 24
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// M = floor(2^24 / Q) = 5039
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// M*Q = 16,774,831 < 2^24 → floor(x/Q) may be 1 too low
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// Correction: remainder = x - q_approx*Q; if rem >= Q, q→q+1
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// Q*5039 fails at: k*2385 >= 2^24 → k >= 7033; max k ≈ 2047 → safe
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// ===========================================================
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wire [36:0] barrett_prod = dividend * 13'd5039; // 24×13=37b
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wire [11:0] q_approx = barrett_prod[35:24]; // quotient estimate
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// q*Q = q*2048 + q*512 + q*256 + q (3329 = 2048+512+256+1)
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wire [23:0] q_times_Q = ({q_approx, 11'd0})
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+ ({q_approx, 9'd0})
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+ ({q_approx, 8'd0})
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+ q_approx;
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wire [24:0] delta = {1'b0, dividend} - {1'b0, q_times_Q}; // 25b
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wire [11:0] comp_q = q_approx + (delta >= {13'b0, 12'(`Q)});
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// lower d bits = compressed result
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wire [11:0] comp_res = comp_q & ({12'b0, two_pow_d} - 1'b1);
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// ===========================================================
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// Decompress: dividend >> d (free), then % Q via Barrett
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// ===========================================================
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wire [23:0] dec_sh = dividend >> d;
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wire [36:0] dm_prod = dec_sh * 13'd5039;
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wire [11:0] dm_qe = dm_prod[35:24];
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wire [23:0] dm_qQ = ({dm_qe, 11'd0})
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+ ({dm_qe, 9'd0})
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+ ({dm_qe, 8'd0})
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+ dm_qe;
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wire [24:0] dm_del = {1'b0, dec_sh} - {1'b0, dm_qQ};
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// divide by Q, take remainder: r = x - q*Q
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wire [12:0] dm_q = dm_qe + (dm_del >= {13'b0, 12'(`Q)}); // corr quotient
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// actual remainder = dec_sh - dm_q*Q
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wire [23:0] dm_corrQ = ({dm_q, 11'd0}) + ({dm_q, 9'd0}) + ({dm_q, 8'd0}) + dm_q;
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wire [24:0] dm_rem = {1'b0, dec_sh} - {1'b0, dm_corrQ};
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// dm_rem < Q*2 (Barrett gives exact quotient after correction), one cond-sub
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wire [11:0] dec_mod = (dm_rem >= {13'b0, 12'(`Q)})
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? (dm_rem[11:0] - 12'(`Q))
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: dm_rem[11:0];
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wire [11:0] mod_result = mode ? dec_mod : comp_res;
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pipeline_reg #(.DW(12)) u_pipe (
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.clk (clk),
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.rst_n (rst_n),
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.data_i (mod_result),
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.valid_i(valid_i),
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.ready_o(ready_o),
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.data_o (coeff_out),
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.valid_o(valid_o),
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.ready_i(ready_i)
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);
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endmodule
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