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290 lines
6.8 KiB
C++
290 lines
6.8 KiB
C++
/*
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LDPC SISO layered decoder
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Copyright 2018 Ahmet Inan <inan@aicodix.de>
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*/
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#ifndef LDPC_DECODER_HH
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#define LDPC_DECODER_HH
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#include <algorithm>
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#include "simd.hh"
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#include "rotate.hh"
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namespace CODE {
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template <typename TABLE, int BETA>
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class LDPCDecoder
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{
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#ifdef __AVX2__
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static const int SIMD_SIZE = 32;
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// M = 360 = 30 * 12
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static const int WORD_SIZE = 30;
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#else
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static const int SIMD_SIZE = 16;
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// M = 360 = 15 * 24
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static const int WORD_SIZE = 15;
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#endif
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static_assert(TABLE::M % WORD_SIZE == 0, "M must be multiple of word size");
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static_assert(WORD_SIZE <= SIMD_SIZE, "SIMD size must be bigger or equal word size");
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static const int M = TABLE::M;
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static const int N = TABLE::N;
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static const int K = TABLE::K;
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static const int R = N-K;
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static const int q = R/M;
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static const int D = WORD_SIZE;
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static const int W = M/D;
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static const int PTY = R/D;
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static const int MSG = K/D;
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static const int CNC = TABLE::LINKS_MAX_CN - 2;
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static const int BNL = (TABLE::LINKS_TOTAL + D-1) / D;
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static const int LOC = (TABLE::LINKS_TOTAL - (2*R-1) + D-1) / D;
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typedef SIMD<int8_t, SIMD_SIZE> TYPE;
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typedef struct { uint16_t off; uint16_t shi; } Loc;
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typedef uint32_t wd_t;
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static_assert(sizeof(wd_t) * 8 >= CNC, "write disable mask needs at least as many bits as max check node links");
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Rotate<TYPE, D> rotate;
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TYPE bnl[BNL];
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TYPE msg[MSG];
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TYPE pty[PTY];
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Loc loc[LOC];
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wd_t wd[PTY];
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uint8_t cnc[q];
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static TYPE eor(TYPE a, TYPE b)
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{
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return vreinterpret<TYPE>(veor(vmask(a), vmask(b)));
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}
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static TYPE orr(TYPE a, TYPE b)
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{
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return vreinterpret<TYPE>(vorr(vmask(a), vmask(b)));
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}
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static TYPE other(TYPE a, TYPE b, TYPE c)
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{
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return vreinterpret<TYPE>(vbsl(vceq(a, b), vmask(c), vmask(b)));
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}
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static TYPE mine(TYPE a, TYPE b)
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{
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return orr(eor(a, b), vdup<TYPE>(127));
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}
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static TYPE selfcorr(TYPE a, TYPE b)
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{
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return vreinterpret<TYPE>(vand(vmask(b), vorr(vceqz(a), veor(vcgtz(a), vcltz(b)))));
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}
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bool bad()
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{
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Loc *lo = loc;
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for (int i = 0; i < q; ++i) {
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int cnt = cnc[i];
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int deg = cnt + 2;
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auto res = vmask(vzero<TYPE>());
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for (int j = 0; j < W; ++j) {
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TYPE cnv = vdup<TYPE>(1);
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for (int k = 0; k < deg; ++k) {
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TYPE tmp;
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if (k < cnt) {
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tmp = rotate(msg[lo[k].off], -lo[k].shi);
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} else if (k == cnt) {
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tmp = pty[W*i+j];
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} else {
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if (i) {
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tmp = pty[W*(i-1)+j];
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} else if (j) {
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tmp = pty[W*(q-1)+j-1];
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} else {
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tmp = rotate(pty[PTY-1], 1);
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tmp.v[0] = 127;
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}
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}
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cnv = vsign(cnv, tmp);
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}
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res = vorr(res, vclez(cnv));
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lo += cnt;
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}
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for (int n = 0; n < D; ++n)
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if (res.v[n])
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return true;
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}
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return false;
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}
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void update()
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{
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TYPE *bl = bnl;
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Loc *lo = loc;
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for (int i = 0; i < q; ++i) {
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int cnt = cnc[i];
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int deg = cnt + 2;
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for (int j = 0; j < W; ++j) {
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TYPE mags[deg], inps[deg];
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TYPE min0 = vdup<TYPE>(127);
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TYPE min1 = vdup<TYPE>(127);
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TYPE signs = vdup<TYPE>(127);
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for (int k = 0; k < deg; ++k) {
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TYPE tmp;
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if (k < cnt) {
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tmp = rotate(msg[lo[k].off], -lo[k].shi);
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} else if (k == cnt) {
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tmp = pty[W*i+j];
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} else {
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if (i) {
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tmp = pty[W*(i-1)+j];
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} else if (j) {
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tmp = pty[W*(q-1)+j-1];
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} else {
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tmp = rotate(pty[PTY-1], 1);
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tmp.v[0] = 127;
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}
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}
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TYPE inp = vqsub(tmp, bl[k]);
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TYPE mag = vqabs(inp);
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if (BETA) {
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auto beta = vunsigned(vdup<TYPE>(BETA));
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mag = vsigned(vqsub(vunsigned(mag), beta));
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}
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min1 = vmin(min1, vmax(min0, mag));
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min0 = vmin(min0, mag);
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signs = eor(signs, inp);
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inps[k] = inp;
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mags[k] = mag;
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}
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for (int k = 0; k < deg; ++k) {
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TYPE mag = mags[k];
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TYPE inp = inps[k];
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TYPE out = vsign(other(mag, min0, min1), mine(signs, inp));
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out = vclamp(out, -32, 31);
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out = selfcorr(bl[k], out);
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TYPE tmp = vqadd(inp, out);
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if (k < cnt) {
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if (!((wd[W*i+j]>>k)&1)) {
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bl[k] = out;
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msg[lo[k].off] = rotate(tmp, lo[k].shi);
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}
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} else if (k == cnt) {
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bl[k] = out;
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pty[W*i+j] = tmp;
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} else {
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bl[k] = out;
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if (i) {
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pty[W*(i-1)+j] = tmp;
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} else if (j) {
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pty[W*(q-1)+j-1] = tmp;
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} else {
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tmp.v[0] = pty[PTY-1].v[D-1];
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pty[PTY-1] = rotate(tmp, -1);
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}
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}
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}
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if (wd[W*i+j]) {
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for (int first = 0, c = 1; c < cnt; ++c) {
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if (lo[first].off != lo[c].off || c == cnt-1) {
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int last = c - 1;
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if (c == cnt-1)
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++last;
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if (last != first) {
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int count = last - first + 1;
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wd_t mask = ((1 << count) - 1) << first;
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wd_t cur = wd[W*i+j];
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wd_t tmp = cur & mask;
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wd_t ror = (tmp >> 1) | (tmp << (count-1));
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wd[W*i+j] = (cur & ~mask) | (ror & mask);
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}
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first = c;
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}
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}
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}
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lo += cnt;
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bl += deg;
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}
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}
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//assert(bl <= bnl + BNL);
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//std::cerr << BNL - (bl - bnl) << std::endl;
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}
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public:
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LDPCDecoder()
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{
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uint16_t pos[q * CNC];
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for (int i = 0; i < q; ++i)
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cnc[i] = 0;
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int bit_pos = 0;
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const int *row_ptr = TABLE::POS;
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for (int g = 0; TABLE::LEN[g]; ++g) {
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int bit_deg = TABLE::DEG[g];
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for (int r = 0; r < TABLE::LEN[g]; ++r) {
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for (int d = 0; d < bit_deg; ++d) {
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int n = row_ptr[d] % q;
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int m = row_ptr[d] / q;
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pos[CNC*n+cnc[n]++] = bit_pos + (M - m) % M;
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}
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row_ptr += bit_deg;
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bit_pos += M;
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}
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}
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Loc *lo = loc;
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for (int i = 0; i < q; ++i) {
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int cnt = cnc[i];
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int offset[cnt], shift[cnt];
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for (int c = 0; c < cnt; ++c) {
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shift[c] = pos[CNC*i+c] % M;
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offset[c] = pos[CNC*i+c] - shift[c];
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}
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for (int j = 0; j < W; ++j) {
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for (int c = 0; c < cnt; ++c) {
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lo[c].off = offset[c] / D + shift[c] % W;
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lo[c].shi = shift[c] / W;
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shift[c] = (shift[c] + 1) % M;
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}
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std::sort(lo, lo + cnt, [](const Loc &a, const Loc &b){ return a.off < b.off; });
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wd[W*i+j] = 0;
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for (int c = 0; c < cnt-1; ++c)
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if (lo[c].off == lo[c+1].off)
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wd[W*i+j] |= 1 << c;
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lo += cnt;
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}
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}
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//assert(lo <= loc + LOC);
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//std::cerr << LOC - (lo - loc) << std::endl;
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}
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int operator()(int8_t *message, int8_t *parity, int trials = 25)
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{
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for (int i = 0; i < BNL; ++i)
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bnl[i] = vzero<TYPE>();
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for (int i = 0; i < K/M; ++i)
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for (int j = 0; j < W; ++j)
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for (int n = 0; n < D; ++n)
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msg[W*i+j].v[n] = message[M*i+W*n+j];
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for (int i = 0; i < q; ++i)
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for (int j = 0; j < W; ++j)
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for (int n = 0; n < D; ++n)
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pty[W*i+j].v[n] = parity[q*(W*n+j)+i];
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while (bad() && --trials >= 0)
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update();
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for (int i = 0; i < K/M; ++i)
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for (int j = 0; j < W; ++j)
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for (int n = 0; n < D; ++n)
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message[M*i+W*n+j] = msg[W*i+j].v[n];
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for (int i = 0; i < q; ++i)
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for (int j = 0; j < W; ++j)
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for (int n = 0; n < D; ++n)
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parity[q*(W*n+j)+i] = pty[W*i+j].v[n];
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return trials;
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}
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};
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}
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#endif
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