64 lines
2.6 KiB
C++
64 lines
2.6 KiB
C++
/***************************************************************************
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* Copyright (C) 2021 by Federico Amedeo Izzo IU2NUO, *
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* Niccolò Izzo IU2KIN *
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* Frederik Saraci IU2NRO *
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* Silvano Seva IU2KWO *
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* *
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* Adapted from original code written by Rob Riggs, Mobilinkd LLC *
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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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/**
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* Compute the Golay(24,12) codeword of a given block of data using the M17
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* Golay polynomial.
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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 uint32_t golay_encode24(const uint16_t& data)
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{
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// Compute [23,12] Golay codeword
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uint32_t codeword = data & 0x0FFFF;
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for(size_t i = 0; i < 12; i++)
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{
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if(codeword & 0x01) codeword ^= 0x0C75;
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codeword >>= 1;
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}
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// Append data to codeword, result is checkbits(11) | data(12)
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codeword |= (data << 11);
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// Compute parity and append it to codeword
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return (codeword << 1) | (__builtin_popcount(codeword) & 0x01);
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}
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#endif /* M17_GOLAY_H */
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