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82 lines
2 KiB
C++
82 lines
2 KiB
C++
/*
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Bose Chaudhuri Hocquenghem Encoder
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Copyright 2018 Ahmet Inan <inan@aicodix.de>
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*/
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#ifndef BOSE_CHAUDHURI_HOCQUENGHEM_ENCODER_HH
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#define BOSE_CHAUDHURI_HOCQUENGHEM_ENCODER_HH
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#include <initializer_list>
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namespace CODE {
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template <int NR, int FCR, int MSG, typename GF>
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class BoseChaudhuriHocquenghemEncoder
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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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ValueType generator[NP+1];
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BoseChaudhuriHocquenghemEncoder(std::initializer_list<int> minimal_polynomials)
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{
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// $generator(x) = \prod_i(minpoly_i(x))$
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int generator_degree = 1;
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generator[0] = ValueType(1);
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for (int i = 1; i <= NP; ++i)
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generator[i] = ValueType(0);
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for (auto m: minimal_polynomials) {
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assert(0 < m && m < 1<<(GF::M+1));
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int m_degree = GF::M;
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while (!(m>>m_degree))
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--m_degree;
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assert(generator_degree + m_degree <= NP + 1);
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for (int i = generator_degree; i >= 0; --i) {
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if (!generator[i])
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continue;
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generator[i] = ValueType(m&1);
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for (int j = 1; j <= m_degree; ++j)
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generator[i+j] += ValueType((m>>j)&1);
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}
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generator_degree += m_degree;
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}
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assert(generator_degree == NP + 1);
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if (0) {
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IndexType root(FCR), pe(1);
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for (int i = 0; i < NR; ++i) {
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ValueType tmp(generator[NP]);
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for (int j = 1; j <= NP; ++j)
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tmp = fma(root, tmp, generator[NP-j]);
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assert(!tmp);
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root *= pe;
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}
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std::cerr << "generator =";
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for (int i = 0; i <= NP; ++i)
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std::cerr << " " << (int)generator[i];
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std::cerr << std::endl;
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}
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}
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void operator()(ValueType *code)
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{
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// $code = data * x^{NP} + (data * x^{NP}) \mod{generator}$
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for (int i = 0; i < NP; ++i)
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code[K+i] = ValueType(0);
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for (int i = 0; i < K; ++i) {
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if (code[i] != code[K]) {
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for (int j = 1; j < NP; ++j)
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code[K+j-1] = generator[NP-j] + code[K+j];
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code[N-1] = generator[0];
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} else {
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for (int j = 1; j < NP; ++j)
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code[K+j-1] = code[K+j];
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code[N-1] = ValueType(0);
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}
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}
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}
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};
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}
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#endif
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