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155 lines
3.5 KiB
C
155 lines
3.5 KiB
C
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/*
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LDPC SISO layered decoder
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Copyright 2018 Ahmet Inan <xdsopl@gmail.com>
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*/
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#ifndef LAYERED_DECODER_HH
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#define LAYERED_DECODER_HH
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#include <stdlib.h>
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#include "ldpc.h"
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namespace ldpctool {
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template <typename TYPE, typename ALG>
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class LDPCDecoder
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{
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TYPE *bnl, *pty, *inp, *out;
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uint16_t *pos;
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uint8_t *cnc;
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ALG alg;
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int M, N, K, R, q, CNL, LT;
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bool initialized;
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void reset()
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{
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for (int i = 0; i < LT; ++i)
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bnl[i] = alg.zero();
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}
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bool bad(TYPE *data, TYPE *parity, int blocks)
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{
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for (int i = 0; i < q; ++i) {
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int cnt = cnc[i];
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for (int j = 0; j < M; ++j) {
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TYPE cnv = alg.sign(alg.one(), parity[M*i+j]);
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if (i)
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cnv = alg.sign(cnv, parity[M*(i-1)+j]);
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else if (j)
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cnv = alg.sign(cnv, parity[j+(q-1)*M-1]);
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for (int c = 0; c < cnt; ++c)
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cnv = alg.sign(cnv, data[pos[CNL*(M*i+j)+c]]);
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if (alg.bad(cnv, blocks))
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return true;
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}
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}
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return false;
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}
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void update(TYPE *data, TYPE *parity)
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{
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TYPE *bl = bnl;
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for (int i = 0; i < q; ++i) {
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int cnt = cnc[i];
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for (int j = 0; j < M; ++j) {
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int deg = cnt + 2 - !(i|j);
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for (int c = 0; c < cnt; ++c)
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inp[c] = out[c] = alg.sub(data[pos[CNL*(M*i+j)+c]], bl[c]);
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inp[cnt] = out[cnt] = alg.sub(parity[M*i+j], bl[cnt]);
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if (i)
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inp[cnt+1] = out[cnt+1] = alg.sub(parity[M*(i-1)+j], bl[cnt+1]);
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else if (j)
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inp[cnt+1] = out[cnt+1] = alg.sub(parity[j+(q-1)*M-1], bl[cnt+1]);
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alg.finalp(out, deg);
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for (int d = 0; d < deg; ++d)
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alg.update(bl+d, out[d]);
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for (int c = 0; c < cnt; ++c)
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data[pos[CNL*(M*i+j)+c]] = alg.add(inp[c], bl[c]);
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parity[M*i+j] = alg.add(inp[cnt], bl[cnt]);
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if (i)
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parity[M*(i-1)+j] = alg.add(inp[cnt+1], bl[cnt+1]);
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else if (j)
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parity[j+(q-1)*M-1] = alg.add(inp[cnt+1], bl[cnt+1]);
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bl += deg;
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}
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}
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}
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public:
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LDPCDecoder() : initialized(false)
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{
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}
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void init(LDPCInterface *it)
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{
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if (initialized) {
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free(bnl);
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free(pty);
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delete[] cnc;
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delete[] pos;
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delete[] inp;
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delete[] out;
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}
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initialized = true;
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LDPCInterface *ldpc = it->clone();
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N = ldpc->code_len();
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K = ldpc->data_len();
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M = ldpc->group_len();
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R = N - K;
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q = R / M;
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CNL = ldpc->links_max_cn() - 2;
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pos = new uint16_t[R * CNL];
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cnc = new uint8_t[R];
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inp = new TYPE[N];
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out = new TYPE[N];
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for (int i = 0; i < R; ++i)
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cnc[i] = 0;
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ldpc->first_bit();
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for (int j = 0; j < K; ++j) {
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int *acc_pos = ldpc->acc_pos();
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int bit_deg = ldpc->bit_deg();
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for (int n = 0; n < bit_deg; ++n) {
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int i = acc_pos[n];
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pos[CNL*i+cnc[i]++] = j;
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}
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ldpc->next_bit();
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}
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LT = ldpc->links_total();
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delete ldpc;
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bnl = reinterpret_cast<TYPE *>(aligned_alloc(sizeof(TYPE), sizeof(TYPE) * LT));
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pty = reinterpret_cast<TYPE *>(aligned_alloc(sizeof(TYPE), sizeof(TYPE) * R));
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uint16_t *tmp = new uint16_t[R * CNL];
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for (int i = 0; i < q; ++i)
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for (int j = 0; j < M; ++j)
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for (int c = 0; c < CNL; ++c)
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tmp[CNL*(M*i+j)+c] = pos[CNL*(q*j+i)+c];
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delete[] pos;
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pos = tmp;
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}
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int operator()(TYPE *data, TYPE *parity, int trials = 25, int blocks = 1)
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{
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reset();
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for (int i = 0; i < q; ++i)
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for (int j = 0; j < M; ++j)
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pty[M*i+j] = parity[q*j+i];
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while (bad(data, pty, blocks) && --trials >= 0)
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update(data, pty);
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for (int i = 0; i < q; ++i)
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for (int j = 0; j < M; ++j)
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parity[q*j+i] = pty[M*i+j];
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return trials;
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}
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~LDPCDecoder()
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{
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if (initialized) {
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free(bnl);
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free(pty);
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delete[] cnc;
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delete[] pos;
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delete[] inp;
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delete[] out;
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}
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}
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};
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} // namespace ldpctool
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#endif
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