96 lines
3.4 KiB
C++
96 lines
3.4 KiB
C++
/***************************************************************************
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* Copyright (C) 2021 - 2023 by Federico Amedeo Izzo IU2NUO, *
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* Niccolò Izzo IU2KIN *
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* Wojciech Kaczmarski SP5WWP *
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* Frederik Saraci IU2NRO *
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* Silvano Seva IU2KWO *
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* *
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 3 of the License, or *
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* (at your option) any later version. *
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* *
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* This program is distributed in the hope that it will be useful, *
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* but WITHOUT ANY WARRANTY; without even the implied warranty of *
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
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* GNU General Public License for more details. *
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* *
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* You should have received a copy of the GNU General Public License *
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* along with this program; if not, see <http://www.gnu.org/licenses/> *
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***************************************************************************/
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#ifndef M17_GOLAY_H
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#define M17_GOLAY_H
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#ifndef __cplusplus
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#error This header is C++ only!
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#endif
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#include <cstdint>
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namespace M17
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{
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namespace Golay24
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{
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/**
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* Function computing the Golay(24,12) checksum of a given 12-bit data block.
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*
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* @param value: input data.
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* @return Golay(24,12) checksum.
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*/
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uint16_t calcChecksum(const uint16_t& value);
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/**
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* Detect and correct errors in a Golay(24,12) codeword.
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*
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* @param codeword: input codeword.
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* @return bitmask corresponding to detected bit errors in the codeword, or
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* 0xFFFFFFFF if bit errors are unrecoverable.
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*/
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uint32_t detectErrors(const uint32_t& codeword);
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} // namespace Golay24
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/**
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* Compute the Golay(24,12) codeword of a given block of data using the
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* generator polynomial 0xC75.
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* Result is composed as follows:
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*
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* +--------+----------+--------+
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* | parity | checksum | data |
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* +--------+----------+--------+
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* | 1 bit | 11 bit | 12 bit |
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* +--------+----------+--------+
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*
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* \param data: input data, upper four bits are discarded.
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* \return resulting 24 bit codeword.
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*/
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static inline uint32_t golay24_encode(const uint16_t& data)
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{
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return (data << 12) | Golay24::calcChecksum(data);
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}
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/**
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* Decode a Golay(24,12) codeword, correcting eventual bit errors. In case the
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* bit errors are not correctable, the function returns 0xFFFF, a value outside
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* the range allowed for the 12-bit input data required by Golay coding.
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*
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* \param codeword: input Golay(24,12) codeword.
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* \return original data block or 0xFFFF in case of unrecoverable errors.
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*/
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static inline uint16_t golay24_decode(const uint32_t& codeword)
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{
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uint32_t errors = Golay24::detectErrors(codeword);
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if(errors == 0xFFFFFFFF) return 0xFFFF;
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return ((codeword ^ errors) >> 12) & 0x0FFF;
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}
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} // namespace M17
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#endif // M17_GOLAY_H
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