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