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keep non-bitpacked BCH decoder as reference
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Ahmet Inan
parent
de2ef34eb3
commit
deb6ede15f
2 changed files with 74 additions and 18 deletions
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@ -14,6 +14,63 @@ namespace CODE {
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template <int NR, int FCR, int MSG, typename GF>
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class BoseChaudhuriHocquenghemDecoder
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{
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public:
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typedef typename GF::value_type value_type;
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typedef typename GF::ValueType ValueType;
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typedef typename GF::IndexType IndexType;
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static const int N = GF::N, K = MSG, NP = N - K;
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ReedSolomonErrorCorrection<NR, FCR, GF> algorithm;
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int compute_syndromes(uint8_t *code, ValueType *syndromes)
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{
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// $syndromes_i = code(pe^{FCR+i})$
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for (int i = 0; i < NR; ++i)
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syndromes[i] = ValueType((code[0] >> 7) & 1);
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for (int j = 1; j < N; ++j) {
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IndexType root(FCR), pe(1);
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for (int i = 0; i < NR; ++i) {
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syndromes[i] = fma(root, syndromes[i], ValueType((code[j / 8] >> (7 - j % 8)) & 1));
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root *= pe;
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}
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}
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int nonzero = 0;
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for (int i = 0; i < NR; ++i)
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nonzero += !!syndromes[i];
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return nonzero;
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}
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int compute_syndromes(uint8_t *code, value_type *syndromes)
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{
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return compute_syndromes(code, reinterpret_cast<ValueType *>(syndromes));
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}
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int operator()(uint8_t *code, value_type *erasures = 0, int erasures_count = 0)
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{
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assert(0 <= erasures_count && erasures_count <= NR);
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if (0) {
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for (int i = 0; i < erasures_count; ++i)
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code[erasures[i] / 8] &= ~(128 >> (erasures[i] % 8));
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}
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ValueType syndromes[NR];
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if (!compute_syndromes(code, syndromes))
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return 0;
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IndexType locations[NR];
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ValueType magnitudes[NR];
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int count = algorithm(syndromes, locations, magnitudes, reinterpret_cast<IndexType *>(erasures), erasures_count);
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if (count <= 0)
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return count;
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for (int i = 0; i < count; ++i)
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if (1 < (int)magnitudes[i])
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return -1;
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for (int i = 0; i < count; ++i)
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code[(int)locations[i] / 8] ^= (int)magnitudes[i] << (7 - (int)locations[i] % 8);
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int corrections_count = 0;
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for (int i = 0; i < count; ++i)
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corrections_count += !!magnitudes[i];
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return corrections_count;
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}
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};
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template <int NR, int FCR, int MSG, typename GF>
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class BoseChaudhuriHocquenghemDecoderReference
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{
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public:
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typedef typename GF::value_type value_type;
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typedef typename GF::ValueType ValueType;
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@ -62,52 +119,6 @@ public:
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corrections_count += !!magnitudes[i];
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return corrections_count;
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}
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int compute_syndromes(uint8_t *code, ValueType *syndromes)
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{
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// $syndromes_i = code(pe^{FCR+i})$
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for (int i = 0; i < NR; ++i)
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syndromes[i] = ValueType((code[0] >> 7) & 1);
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for (int j = 1; j < N; ++j) {
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IndexType root(FCR), pe(1);
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for (int i = 0; i < NR; ++i) {
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syndromes[i] = fma(root, syndromes[i], ValueType((code[j / 8] >> (7 - j % 8)) & 1));
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root *= pe;
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}
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}
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int nonzero = 0;
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for (int i = 0; i < NR; ++i)
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nonzero += !!syndromes[i];
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return nonzero;
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}
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int compute_syndromes(uint8_t *code, value_type *syndromes)
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{
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return compute_syndromes(code, reinterpret_cast<ValueType *>(syndromes));
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}
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int operator()(uint8_t *code, value_type *erasures = 0, int erasures_count = 0)
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{
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assert(0 <= erasures_count && erasures_count <= NR);
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if (0) {
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for (int i = 0; i < erasures_count; ++i)
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code[erasures[i] / 8] &= ~(128 >> (erasures[i] % 8));
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}
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ValueType syndromes[NR];
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if (!compute_syndromes(code, syndromes))
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return 0;
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IndexType locations[NR];
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ValueType magnitudes[NR];
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int count = algorithm(syndromes, locations, magnitudes, reinterpret_cast<IndexType *>(erasures), erasures_count);
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if (count <= 0)
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return count;
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for (int i = 0; i < count; ++i)
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if (1 < (int)magnitudes[i])
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return -1;
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for (int i = 0; i < count; ++i)
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code[(int)locations[i] / 8] ^= (int)magnitudes[i] << (7 - (int)locations[i] % 8);
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int corrections_count = 0;
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for (int i = 0; i < count; ++i)
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corrections_count += !!magnitudes[i];
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return corrections_count;
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}
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};
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}
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@ -67,6 +67,51 @@ int main()
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delete decode;
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delete instance;
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}
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if (0) {
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// NASA INTRO BCH(15, 5) T=3
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typedef CODE::GaloisField<4, 0b10011, uint8_t> GF;
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typedef CODE::BoseChaudhuriHocquenghemDecoderReference<6, 1, 5, GF> BCH;
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GF instance;
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BCH decode;
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uint8_t target[BCH::N] = { 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 1, 0 };
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uint8_t code[BCH::N];
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for (int i = 0; i < BCH::N; ++i)
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code[i] = target[i];
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std::uniform_int_distribution<uint8_t> distribution(0, BCH::N-1);
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auto noise = std::bind(distribution, generator);
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for (int i = 0; i < 3; ++i)
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code[noise()] ^= 1;
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decode(reinterpret_cast<GF::ValueType *>(code));
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for (int i = 0; i < BCH::N; ++i)
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assert(code[i] == target[i]);
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}
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if (0) {
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// DVB-S2 FULL BCH(65535, 65343) T=12
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typedef CODE::GaloisField<16, 0b10000000000101101, uint16_t> GF;
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typedef CODE::BoseChaudhuriHocquenghemDecoderReference<24, 1, 65343, GF> BCH;
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GF *instance = new GF();
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BCH *decode = new BCH();
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uint16_t *target = new uint16_t[BCH::N];
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for (int i = 0, s = 0; i < BCH::K; ++i, s=(s*(s*s*51767+71287)+35149)&0xffffff)
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target[i] = (s^=s>>7)&1;
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uint16_t parity[BCH::NP] = { 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0 };
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for (int i = 0; i < BCH::NP; ++i)
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target[BCH::K+i] = parity[i];
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uint16_t *code = new uint16_t[BCH::N];
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for (int i = 0; i < BCH::N; ++i)
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code[i] = target[i];
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std::uniform_int_distribution<uint16_t> distribution(0, BCH::N-1);
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auto noise = std::bind(distribution, generator);
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for (int i = 0; i < 12; ++i)
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code[noise()] ^= 1;
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(*decode)(reinterpret_cast<GF::ValueType *>(code));
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for (int i = 0; i < BCH::N; ++i)
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assert(code[i] == target[i]);
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delete[] target;
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delete[] code;
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delete decode;
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delete instance;
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}
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std::cerr << "Bose Chaudhuri Hocquenghem Decoder test passed!" << std::endl;
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return 0;
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}
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