kopia lustrzana https://github.com/f4exb/sdrangel
138 wiersze
2.9 KiB
C++
138 wiersze
2.9 KiB
C++
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#include "Util.h"
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#include "Golay24.h"
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namespace mobilinkd {
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std::array<Golay24::SyndromeMapEntry, Golay24::LUT_SIZE> Golay24::LUT = Golay24::make_lut();
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Golay24::Golay24()
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{}
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uint32_t Golay24::syndrome(uint32_t codeword)
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{
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codeword &= 0xffffffl;
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for (size_t i = 0; i != 12; ++i)
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{
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if (codeword & 1) {
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codeword ^= POLY;
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}
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codeword >>= 1;
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}
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return (codeword << 12);
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}
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bool Golay24::parity(uint32_t codeword)
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{
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return popcount(codeword) & 1;
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}
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Golay24::SyndromeMapEntry Golay24::makeSyndromeMapEntry(uint64_t val)
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{
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return SyndromeMapEntry{uint32_t(val >> 16), uint16_t(val & 0xFFFF)};
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}
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uint64_t Golay24::makeSME(uint64_t syndrome, uint32_t bits)
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{
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return (syndrome << 24) | (bits & 0xFFFFFF);
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}
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uint32_t Golay24::encode23(uint16_t data)
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{
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// data &= 0xfff;
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uint32_t codeword = data;
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for (size_t i = 0; i != 12; ++i)
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{
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if (codeword & 1) {
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codeword ^= POLY;
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}
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codeword >>= 1;
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}
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return codeword | (data << 11);
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}
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uint32_t Golay24::encode24(uint16_t data)
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{
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auto codeword = encode23(data);
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return ((codeword << 1) | parity(codeword));
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}
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bool Golay24::decode(uint32_t input, uint32_t& output)
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{
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auto syndrm = syndrome(input >> 1);
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auto it = std::lower_bound(
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LUT.begin(),
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LUT.end(),
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syndrm,
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[](const SyndromeMapEntry& sme, uint32_t val){
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return (sme.a >> 8) < val;
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}
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);
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if ((it->a >> 8) == syndrm)
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{
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// Build the correction from the compressed entry.
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auto correction = ((((it->a & 0xFF) << 16) | it->b) << 1);
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// Apply the correction to the input.
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output = input ^ correction;
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// Only test parity for 3-bit errors.
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return popcount(syndrm) < 3 || !parity(output);
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}
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return false;
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}
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std::array<Golay24::SyndromeMapEntry, Golay24::LUT_SIZE> Golay24::make_lut()
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{
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constexpr size_t VECLEN=23;
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Golay24_detail::array<uint64_t, LUT_SIZE> result{};
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size_t index = 0;
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result[index++] = makeSME(syndrome(0), 0);
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for (size_t i = 0; i != VECLEN; ++i)
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{
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auto v = (1 << i);
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result[index++] = makeSME(syndrome(v), v);
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}
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for (size_t i = 0; i != VECLEN - 1; ++i)
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{
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for (size_t j = i + 1; j != VECLEN; ++j)
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{
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auto v = (1 << i) | (1 << j);
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result[index++] = makeSME(syndrome(v), v);
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}
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}
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for (size_t i = 0; i != VECLEN - 2; ++i)
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{
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for (size_t j = i + 1; j != VECLEN - 1; ++j)
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{
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for (size_t k = j + 1; k != VECLEN; ++k)
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{
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auto v = (1 << i) | (1 << j) | (1 << k);
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result[index++] = makeSME(syndrome(v), v);
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}
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}
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}
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result = Golay24_detail::sort(result);
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std::array<SyndromeMapEntry, LUT_SIZE> tmp;
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for (size_t i = 0; i != LUT_SIZE; ++i)
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{
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tmp[i] = makeSyndromeMapEntry(result[i]);
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}
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return tmp;
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}
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} // mobilinkd
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