Node / RFnexus / code.git / files / reed_solomon_encoder.hh

Displaying Raw • Download

/*

Reed Solomon Encoder

Copyright 2018 Ahmet Inan <inan@aicodix.de>

*/

#pragma once

namespace CODE {

template <int ROOTS, int FCR, typename GF>

class ReedSolomonEncoder

{

public:

typedef typename GF::value_type value_type;

typedef typename GF::ValueType ValueType;

typedef typename GF::IndexType IndexType;

static const int NR = ROOTS;

static const int N = GF::N, K = N - NR, NP = NR;

private:

IndexType generator[NR+1];

public:

ReedSolomonEncoder()

{

// $generator = \\prod_{i=0}^{NR}(x-pe^{FCR+i})$

ValueType tmp[NR+1];

IndexType root(FCR), pe(1);

for (int i = 0; i < NR; ++i) {

tmp[i] = ValueType(1);

for (int j = i; j > 0; --j)

tmp[j] = fma(root, tmp[j], tmp[j-1]);

tmp[0] *= root;

root *= pe;

}

tmp[NR] = ValueType(1);

if (0) {

std::cerr << "generator = ";

for (int i = NR; i > 0; --i) {

if (!tmp[i])

continue;

if (tmp[i] != ValueType(1))

std::cerr << (int)tmp[i] << "*";

std::cerr << "x";

if (i != 1)

std::cerr << "^" << i;

std::cerr << " + ";

}

std::cerr << (int)tmp[0] << std::endl;

}

for (int i = 0; i <= NR; ++i)

generator[i] = index(tmp[i]);

}

void operator()(const ValueType *data, ValueType *parity, int data_len = K)

{

assert(0 < data_len && data_len <= K);

// $code = data * x^{NR} + (data * x^{NR}) \\mod{generator}$

for (int i = 0; i < NR; ++i)

parity[i] = ValueType(0);

for (int i = 0; i < data_len; ++i) {

ValueType feedback = data[i] + parity[0];

if (feedback) {

IndexType fb = index(feedback);

for (int j = 1; j < NR; ++j)

parity[j-1] = fma(fb, generator[NR-j], parity[j]);

parity[NP-1] = value(generator[0] * fb);

} else {

for (int j = 1; j < NR; ++j)

parity[j-1] = parity[j];

parity[NP-1] = ValueType(0);

}

}

}

void operator()(const value_type *data, value_type *parity, int data_len = K)

{

(*this)(reinterpret_cast<const ValueType *>(data), reinterpret_cast<ValueType *>(parity), data_len);

}

};

}