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added LDPC decoder version with fully computed LUT
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Ahmet Inan
parent
e06c954148
commit
b41799c84d
4 changed files with 242 additions and 1 deletions
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@ -55,7 +55,13 @@ Implemented are the following Encoders and Decoders:
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### [ldpc_decoder.hh](ldpc_decoder.hh)
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[Low-density parity-check](https://en.wikipedia.org/wiki/Low-density_parity-check_code) layered decoder
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[Low-density parity-check](https://en.wikipedia.org/wiki/Low-density_parity-check_code) layered decoder
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This version stores only the first q bit positions and might be faster on low power systems.
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### [ldpc_decoder2.hh](ldpc_decoder2.hh)
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[Low-density parity-check](https://en.wikipedia.org/wiki/Low-density_parity-check_code) layered decoder
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This version stores and uses all bit positions and might be faster on high performance workstations.
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### [exclusive_reduce.hh](exclusive_reduce.hh)
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@ -1,6 +1,8 @@
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/*
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LDPC SISO layered decoder
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This version stores only the first q bit positions
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Copyright 2018 Ahmet Inan <inan@aicodix.de>
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*/
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229
ldpc_decoder2.hh
Normal file
229
ldpc_decoder2.hh
Normal file
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@ -0,0 +1,229 @@
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/*
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LDPC SISO layered decoder v2
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This version stores and uses all bit positions
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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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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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#else
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static const int SIMD_SIZE = 16;
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#endif
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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 CNC = TABLE::LINKS_MAX_CN - 2;
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static const int BNL = TABLE::LINKS_TOTAL / SIMD_SIZE + TABLE::LINKS_MAX_CN * q;
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typedef SIMD<int8_t, SIMD_SIZE> TYPE;
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TYPE bnl[BNL];
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int8_t pty[R];
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uint16_t pos[R * CNC];
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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 void finalp(TYPE *links, int cnt)
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{
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auto beta = vunsigned(vdup<TYPE>(BETA));
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TYPE mags[cnt];
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for (int i = 0; i < cnt; ++i)
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mags[i] = vsigned(vqsub(vunsigned(vqabs(links[i])), beta));
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TYPE mins[2];
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mins[0] = vmin(mags[0], mags[1]);
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mins[1] = vmax(mags[0], mags[1]);
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for (int i = 2; i < cnt; ++i) {
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mins[1] = vmin(mins[1], vmax(mins[0], mags[i]));
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mins[0] = vmin(mins[0], mags[i]);
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}
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TYPE signs = links[0];
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for (int i = 1; i < cnt; ++i)
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signs = eor(signs, links[i]);
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for (int i = 0; i < cnt; ++i)
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links[i] = vsign(other(mags[i], mins[0], mins[1]), mine(signs, links[i]));
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}
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bool bad(int8_t *data, int8_t *parity)
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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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auto res = vmask(vzero<TYPE>());
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for (int j = 0; j < M; j += SIMD_SIZE) {
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int num = std::min(M - j, SIMD_SIZE);
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TYPE par[2];
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if (i) {
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for (int n = 0; n < num; ++n)
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par[0].v[n] = parity[M*(i-1)+j+n];
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} else if (j) {
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for (int n = 0; n < num; ++n)
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par[0].v[n] = parity[M*(q-1)-1+j+n];
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} else {
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par[0].v[0] = 127;
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for (int n = 1; n < num; ++n)
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par[0].v[n] = parity[M*(q-1)-1+j+n];
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}
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for (int n = 0; n < num; ++n)
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par[1].v[n] = parity[M*i+j+n];
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TYPE dat[cnt];
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for (int c = 0; c < cnt; ++c)
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for (int n = 0; n < num; ++n)
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dat[c].v[n] = data[pos[CNC*(M*i+j+n)+c]];
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TYPE cnv = vdup<TYPE>(1);
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for (int c = 0; c < 2; ++c)
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cnv = vsign(cnv, par[c]);
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for (int c = 0; c < cnt; ++c)
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cnv = vsign(cnv, dat[c]);
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for (int n = num; n < SIMD_SIZE; ++n)
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cnv.v[n] = 1;
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res = vorr(res, vclez(cnv));
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}
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for (int n = 0; n < SIMD_SIZE; ++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(int8_t *data, int8_t *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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int deg = cnt + 2;
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for (int j = 0; j < M; j += SIMD_SIZE) {
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int num = std::min(M - j, SIMD_SIZE);
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TYPE par[2];
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if (i) {
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for (int n = 0; n < num; ++n)
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par[0].v[n] = parity[M*(i-1)+j+n];
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} else if (j) {
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for (int n = 0; n < num; ++n)
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par[0].v[n] = parity[M*(q-1)-1+j+n];
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} else {
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par[0].v[0] = 127;
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for (int n = 1; n < num; ++n)
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par[0].v[n] = parity[M*(q-1)-1+j+n];
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}
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for (int n = 0; n < num; ++n)
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par[1].v[n] = parity[M*i+j+n];
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TYPE dat[cnt];
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for (int c = 0; c < cnt; ++c)
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for (int n = 0; n < num; ++n)
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dat[c].v[n] = data[pos[CNC*(M*i+j+n)+c]];
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TYPE inp[deg], out[deg];
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for (int c = 0; c < cnt; ++c)
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inp[c] = out[c] = vqsub(dat[c], bl[c]);
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inp[cnt] = out[cnt] = vqsub(par[0], bl[cnt]);
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inp[cnt+1] = out[cnt+1] = vqsub(par[1], bl[cnt+1]);
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finalp(out, deg);
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for (int c = 0; c < cnt; ++c)
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dat[c] = vqadd(inp[c], out[c]);
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par[0] = vqadd(inp[cnt], out[cnt]);
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par[1] = vqadd(inp[cnt+1], out[cnt+1]);
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for (int d = 0; d < deg; ++d)
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*bl++ = vclamp(out[d], -32, 31);
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if (i) {
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for (int n = 0; n < num; ++n)
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parity[M*(i-1)+j+n] = par[0].v[n];
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} else if (j) {
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for (int n = 0; n < num; ++n)
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parity[M*(q-1)-1+j+n] = par[0].v[n];
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} else {
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for (int n = 1; n < num; ++n)
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parity[M*(q-1)-1+j+n] = par[0].v[n];
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}
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for (int n = 0; n < num; ++n)
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parity[M*i+j+n] = par[1].v[n];
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for (int c = 0; c < cnt; ++c)
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for (int n = 0; n < num; ++n)
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data[pos[CNC*(M*i+j+n)+c]] = dat[c].v[n];
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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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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*M*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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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*M*i+c] % M;
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offset[c] = pos[CNC*M*i+c] - shift[c];
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}
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for (int j = 1; j < M; ++j) {
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for (int c = 0; c < cnt; ++c) {
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shift[c] = (shift[c] + 1) % M;
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pos[CNC*(M*i+j)+c] = offset[c] + shift[c];
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}
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}
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}
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}
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int operator()(int8_t *data, 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 < 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) && --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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};
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}
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#endif
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@ -15,7 +15,11 @@ Copyright 2018 Ahmet Inan <inan@aicodix.de>
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#include <algorithm>
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#include <functional>
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#include "ldpc_encoder.hh"
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#if 0
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#include "ldpc_decoder.hh"
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#else
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#include "ldpc_decoder2.hh"
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#endif
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struct DVB_T2_TABLE_A1
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{
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