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added Reed Solomon error correction

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lifted from my FEC project:
https://github.com/xdsopl/FEC
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Ahmet Inan 2018-09-20 18:04:23 +02:00
commit 01db8f516e
10 changed files with 846 additions and 1 deletions
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reed_solomon_decoder.hh Normal file
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/*
Reed Solomon Decoder
Copyright 2018 Ahmet Inan <inan@aicodix.de>
*/
#ifndef REED_SOLOMON_DECODER_HH
#define REED_SOLOMON_DECODER_HH
#include "reed_solomon_error_correction.hh"
namespace CODE {
template <int NR, int FCR, typename GF>
class ReedSolomonDecoder
{
public:
typedef typename GF::value_type value_type;
typedef typename GF::ValueType ValueType;
typedef typename GF::IndexType IndexType;
static const int N = GF::N, K = N - NR;
ReedSolomonDecoder() {}
int compute_syndromes(ValueType *code, ValueType *syndromes)
{
// $syndromes_i = code(pe^{FCR+i})$
for (int i = 0; i < NR; ++i)
syndromes[i] = code[0];
for (int j = 1; j < N; ++j) {
IndexType root(FCR), pe(1);
for (int i = 0; i < NR; ++i) {
syndromes[i] = fma(root, syndromes[i], code[j]);
root *= pe;
}
}
int nonzero = 0;
for (int i = 0; i < NR; ++i)
nonzero += !!syndromes[i];
return nonzero;
}
int operator()(ValueType *code, IndexType *erasures = 0, int erasures_count = 0)
{
assert(0 <= erasures_count && erasures_count <= NR);
if (0) {
for (int i = 0; i < erasures_count; ++i)
code[(int)erasures[i]] = ValueType(0);
}
ValueType syndromes[NR];
if (!compute_syndromes(code, syndromes))
return 0;
IndexType locations[NR];
ValueType magnitudes[NR];
int count = ReedSolomonErrorCorrection<NR, FCR, GF>::algorithm(syndromes, locations, magnitudes, erasures, erasures_count);
if (count <= 0)
return count;
for (int i = 0; i < count; ++i)
code[(int)locations[i]] += magnitudes[i];
int corrections_count = 0;
for (int i = 0; i < count; ++i)
corrections_count += !!magnitudes[i];
return corrections_count;
}
int operator()(value_type *code, value_type *erasures = 0, int erasures_count = 0)
{
return (*this)(reinterpret_cast<ValueType *>(code), reinterpret_cast<IndexType *>(erasures), erasures_count);
}
int compute_syndromes(value_type *code, value_type *syndromes)
{
return compute_syndromes(reinterpret_cast<ValueType *>(code), reinterpret_cast<ValueType *>(syndromes));
}
};
}
#endif