96 lines
3.4 KiB
C++
96 lines
3.4 KiB
C++
/***************************************************************************
|
|
* Copyright (C) 2021 - 2022 by Federico Amedeo Izzo IU2NUO, *
|
|
* Niccolò Izzo IU2KIN *
|
|
* Wojciech Kaczmarski SP5WWP *
|
|
* Frederik Saraci IU2NRO *
|
|
* Silvano Seva IU2KWO *
|
|
* *
|
|
* *
|
|
* 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 3 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, see <http://www.gnu.org/licenses/> *
|
|
***************************************************************************/
|
|
|
|
#ifndef M17_GOLAY_H
|
|
#define M17_GOLAY_H
|
|
|
|
#ifndef __cplusplus
|
|
#error This header is C++ only!
|
|
#endif
|
|
|
|
#include <cstdint>
|
|
|
|
namespace M17
|
|
{
|
|
|
|
namespace Golay24
|
|
{
|
|
|
|
/**
|
|
* Function computing the Golay(24,12) checksum of a given 12-bit data block.
|
|
*
|
|
* @param value: input data.
|
|
* @return Golay(24,12) checksum.
|
|
*/
|
|
uint16_t calcChecksum(const uint16_t& value);
|
|
|
|
/**
|
|
* Detect and correct errors in a Golay(24,12) codeword.
|
|
*
|
|
* @param codeword: input codeword.
|
|
* @return bitmask corresponding to detected bit errors in the codeword, or
|
|
* 0xFFFFFFFF if bit errors are unrecoverable.
|
|
*/
|
|
uint32_t detectErrors(const uint32_t& codeword);
|
|
|
|
} // namespace Golay24
|
|
|
|
|
|
/**
|
|
* Compute the Golay(24,12) codeword of a given block of data using the
|
|
* generator polynomial 0xC75.
|
|
* Result is composed as follows:
|
|
*
|
|
* +--------+----------+--------+
|
|
* | parity | checksum | data |
|
|
* +--------+----------+--------+
|
|
* | 1 bit | 11 bit | 12 bit |
|
|
* +--------+----------+--------+
|
|
*
|
|
* \param data: input data, upper four bits are discarded.
|
|
* \return resulting 24 bit codeword.
|
|
*/
|
|
static inline uint32_t golay24_encode(const uint16_t& data)
|
|
{
|
|
return (data << 12) | Golay24::calcChecksum(data);
|
|
}
|
|
|
|
|
|
/**
|
|
* Decode a Golay(24,12) codeword, correcting eventual bit errors. In case the
|
|
* bit errors are not correctable, the function returns 0xFFFF, a value outside
|
|
* the range allowed for the 12-bit input data required by Golay coding.
|
|
*
|
|
* \param codeword: input Golay(24,12) codeword.
|
|
* \return original data block or 0xFFFF in case of unrecoverable errors.
|
|
*/
|
|
static inline uint16_t golay24_decode(const uint32_t& codeword)
|
|
{
|
|
uint32_t errors = Golay24::detectErrors(codeword);
|
|
if(errors == 0xFFFFFFFF) return 0xFFFF;
|
|
return ((codeword ^ errors) >> 12) & 0x0FFF;
|
|
}
|
|
|
|
} // namespace M17
|
|
|
|
#endif // M17_GOLAY_H
|