SSB_HighSpeed_Modem/hsmodem/fec.cpp

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2020-11-05 13:11:57 -05:00
/*
* High Speed modem to transfer data in a 2,7kHz SSB channel
* =========================================================
* Author: DJ0ABR
*
* (c) DJ0ABR
* www.dj0abr.de
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
*/
#include "hsmodem.h"
#include <cstddef>
#include <iostream>
#include <string>
#include "fec/schifra_galois_field.hpp"
#include "fec/schifra_galois_field_polynomial.hpp"
#include "fec/schifra_sequential_root_generator_polynomial_creator.hpp"
#include "fec/schifra_reed_solomon_encoder.hpp"
#include "fec/schifra_reed_solomon_decoder.hpp"
#include "fec/schifra_reed_solomon_block.hpp"
#include "fec/schifra_error_processes.hpp"
/* Finite Field Parameters */
const std::size_t field_descriptor = 8;
const std::size_t generator_polynomial_index = 120;
const std::size_t generator_polynomial_root_count = FECLEN;
/* Reed Solomon Code Parameters */
const std::size_t code_length = FECBLOCKLEN;
const std::size_t fec_length = FECLEN;
const std::size_t data_length = code_length - fec_length;
/* Instantiate Finite Field and Generator Polynomials */
const schifra::galois::field field(field_descriptor,
schifra::galois::primitive_polynomial_size06,
schifra::galois::primitive_polynomial06);
schifra::galois::field_polynomial generator_polynomial(field);
/* Instantiate Encoder and Decoder (Codec) */
typedef schifra::reed_solomon::encoder<code_length,fec_length,data_length> encoder_t;
typedef schifra::reed_solomon::decoder<code_length,fec_length,data_length> decoder_t;
int cfec_Reconstruct(uint8_t *darr, uint8_t *destination)
{
schifra::reed_solomon::block<code_length,fec_length> rxblock;
for(std::size_t i=0; i<code_length; i++)
rxblock.data[i] = darr[i];
const decoder_t decoder(field, generator_polynomial_index);
if (!decoder.decode(rxblock))
{
// FEC decoding not possible
return 0;
}
for(std::size_t i=0; i<data_length; i++)
destination[i] = rxblock[i];
return 1;
}
void GetFEC(uint8_t *txblock, int len, uint8_t *destArray)
{
schifra::reed_solomon::block<code_length,fec_length> block;
// fill payload into an FEC-block
for(std::size_t i=0; i<data_length; i++)
block.data[i] = txblock[i];
/* Transform message into Reed-Solomon encoded codeword */
const encoder_t encoder(field, generator_polynomial);
if (!encoder.encode(block))
{
// encoding not possible, should never happen
return;
}
// get result out of the FEC block
for(std::size_t i=0; i<code_length; i++)
destArray[i] = block[i];
}
void initFEC()
{
if (!schifra::make_sequential_root_generator_polynomial( field,
generator_polynomial_index,
generator_polynomial_root_count,
generator_polynomial))
{
std::cout << "Error - Failed to create sequential root generator!" << std::endl;
return;
}
}