mirror of
https://github.com/f4exb/sdrangel.git
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275 lines
9.9 KiB
C++
275 lines
9.9 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2020 Edouard Griffiths, F4EXB //
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// //
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// Inspired by: https://github.com/myriadrf/LoRa-SDR //
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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 as 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 V3 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 PLUGINS_CHANNELTX_MODCHIRPCHAT_CHIRPCHATMODENCODERLORA_H_
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#define PLUGINS_CHANNELTX_MODCHIRPCHAT_CHIRPCHATMODENCODERLORA_H_
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#include <vector>
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#include <QByteArray>
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class ChirpChatModEncoderLoRa
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{
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public:
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static void addChecksum(QByteArray& bytes);
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static void encodeBytes(
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const QByteArray& bytes,
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std::vector<unsigned short>& symbols,
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unsigned int nbSymbolBits,
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bool hasHeader,
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bool hasCRC,
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unsigned int nbParityBits
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);
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private:
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static void encodeFec(
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std::vector<uint8_t> &codewords,
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unsigned int nbParityBits,
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unsigned int& cOfs,
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unsigned int& dOfs,
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const uint8_t *bytes,
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const unsigned int codewordCount
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);
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static const unsigned int headerParityBits = 4;
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static const unsigned int headerSymbols = 8;
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static const unsigned int headerCodewords = 5;
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/***********************************************************************
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* Round functions
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**********************************************************************/
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static inline unsigned roundUp(unsigned num, unsigned factor)
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{
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return ((num + factor - 1) / factor) * factor;
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}
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/***********************************************************************
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* Encode a 4 bit word into a 8 bits with parity
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* Non standard version used in sx1272.
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* https://en.wikipedia.org/wiki/Hamming_code
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**********************************************************************/
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static inline unsigned char encodeHamming84sx(const unsigned char x)
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{
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auto d0 = (x >> 0) & 0x1;
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auto d1 = (x >> 1) & 0x1;
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auto d2 = (x >> 2) & 0x1;
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auto d3 = (x >> 3) & 0x1;
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unsigned char b = x & 0xf;
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b |= (d0 ^ d1 ^ d2) << 4;
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b |= (d1 ^ d2 ^ d3) << 5;
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b |= (d0 ^ d1 ^ d3) << 6;
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b |= (d0 ^ d2 ^ d3) << 7;
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return b;
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}
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/***********************************************************************
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* Encode a 4 bit word into a 7 bits with parity.
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* Non standard version used in sx1272.
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**********************************************************************/
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static inline unsigned char encodeHamming74sx(const unsigned char x)
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{
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auto d0 = (x >> 0) & 0x1;
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auto d1 = (x >> 1) & 0x1;
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auto d2 = (x >> 2) & 0x1;
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auto d3 = (x >> 3) & 0x1;
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unsigned char b = x & 0xf;
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b |= (d0 ^ d1 ^ d2) << 4;
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b |= (d1 ^ d2 ^ d3) << 5;
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b |= (d0 ^ d1 ^ d3) << 6;
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return b;
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}
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/***********************************************************************
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* Encode a 4 bit word into a 6 bits with parity.
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**********************************************************************/
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static inline unsigned char encodeParity64(const unsigned char b)
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{
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auto x = b ^ (b >> 1) ^ (b >> 2);
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auto y = x ^ b ^ (b >> 3);
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return ((x & 1) << 4) | ((y & 1) << 5) | (b & 0xf);
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}
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/***********************************************************************
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* Encode a 4 bit word into a 5 bits with parity.
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**********************************************************************/
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static inline unsigned char encodeParity54(const unsigned char b)
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{
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auto x = b ^ (b >> 2);
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x = x ^ (x >> 1);
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return (b & 0xf) | ((x << 4) & 0x10);
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}
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/***********************************************************************
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* CRC reverse engineered from Sx1272 data stream.
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* Modified CCITT crc with masking of the output with an 8bit lfsr
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**********************************************************************/
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static inline uint16_t crc16sx(uint16_t crc, const uint16_t poly)
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{
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for (int i = 0; i < 8; i++)
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{
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if (crc & 0x8000) {
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crc = (crc << 1) ^ poly;
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} else {
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crc <<= 1;
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}
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}
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return crc;
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}
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static inline uint8_t xsum8(uint8_t t)
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{
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t ^= t >> 4;
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t ^= t >> 2;
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t ^= t >> 1;
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return (t & 1);
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}
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static inline uint16_t sx1272DataChecksum(const uint8_t *data, int length)
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{
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uint16_t res = 0;
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uint8_t v = 0xff;
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uint16_t crc = 0;
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for (int i = 0; i < length; i++)
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{
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crc = crc16sx(res, 0x1021);
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v = xsum8(v & 0xB8) | (v << 1);
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res = crc ^ data[i];
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}
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res ^= v;
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v = xsum8(v & 0xB8) | (v << 1);
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res ^= v << 8;
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return res;
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}
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/***********************************************************************
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* Specific checksum for header
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**********************************************************************/
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static inline uint8_t headerChecksum(const uint8_t *h)
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{
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auto a0 = (h[0] >> 4) & 0x1;
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auto a1 = (h[0] >> 5) & 0x1;
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auto a2 = (h[0] >> 6) & 0x1;
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auto a3 = (h[0] >> 7) & 0x1;
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auto b0 = (h[0] >> 0) & 0x1;
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auto b1 = (h[0] >> 1) & 0x1;
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auto b2 = (h[0] >> 2) & 0x1;
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auto b3 = (h[0] >> 3) & 0x1;
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auto c0 = (h[1] >> 0) & 0x1;
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auto c1 = (h[1] >> 1) & 0x1;
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auto c2 = (h[1] >> 2) & 0x1;
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auto c3 = (h[1] >> 3) & 0x1;
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uint8_t res;
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res = (a0 ^ a1 ^ a2 ^ a3) << 4;
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res |= (a3 ^ b1 ^ b2 ^ b3 ^ c0) << 3;
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res |= (a2 ^ b0 ^ b3 ^ c1 ^ c3) << 2;
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res |= (a1 ^ b0 ^ b2 ^ c0 ^ c1 ^ c2) << 1;
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res |= a0 ^ b1 ^ c0 ^ c1 ^ c2 ^ c3;
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return res;
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}
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/***********************************************************************
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* Whitening generator reverse engineered from Sx1272 data stream.
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* Each bit of a codeword is combined with the output from a different position in the whitening sequence.
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**********************************************************************/
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static inline void Sx1272ComputeWhitening(uint8_t *buffer, uint16_t bufferSize, const int bitOfs, const int nbParityBits)
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{
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static const int ofs0[8] = {6,4,2,0,-112,-114,-302,-34 }; // offset into sequence for each bit
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static const int ofs1[5] = {6,4,2,0,-360 }; // different offsets used for single parity mode (1 == nbParityBits)
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static const int whiten_len = 510; // length of whitening sequence
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static const uint64_t whiten_seq[8] = { // whitening sequence
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0x0102291EA751AAFFL,0xD24B050A8D643A17L,0x5B279B671120B8F4L,0x032B37B9F6FB55A2L,
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0x994E0F87E95E2D16L,0x7CBCFC7631984C26L,0x281C8E4F0DAEF7F9L,0x1741886EB7733B15L
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};
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const int *ofs = (1 == nbParityBits) ? ofs1 : ofs0;
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int i, j;
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for (j = 0; j < bufferSize; j++)
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{
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uint8_t x = 0;
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for (i = 0; i < 4 + nbParityBits; i++)
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{
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int t = (ofs[i] + j + bitOfs + whiten_len) % whiten_len;
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if (whiten_seq[t >> 6] & ((uint64_t)1 << (t & 0x3F))) {
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x |= 1 << i;
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}
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}
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buffer[j] ^= x;
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}
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}
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/***********************************************************************
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* Diagonal interleaver + deinterleaver
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**********************************************************************/
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static inline void diagonalInterleaveSx(
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const uint8_t *codewords,
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const size_t numCodewords,
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uint16_t *symbols,
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const size_t nbSymbolBits,
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const size_t nbParityBits
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)
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{
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for (size_t x = 0; x < numCodewords / nbSymbolBits; x++)
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{
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const size_t cwOff = x*nbSymbolBits;
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const size_t symOff = x*(4 + nbParityBits);
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for (size_t k = 0; k < 4 + nbParityBits; k++)
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{
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for (size_t m = 0; m < nbSymbolBits; m++)
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{
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const size_t i = (m + k + nbSymbolBits) % nbSymbolBits;
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const auto bit = (codewords[cwOff + i] >> k) & 0x1;
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symbols[symOff + k] |= (bit << m);
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}
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}
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}
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}
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/***********************************************************************
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* https://en.wikipedia.org/wiki/Gray_code
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**********************************************************************/
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/*
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* A more efficient version, for Gray codes of 16 or fewer bits.
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*/
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static inline unsigned short grayToBinary16(unsigned short num)
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{
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num = num ^ (num >> 8);
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num = num ^ (num >> 4);
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num = num ^ (num >> 2);
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num = num ^ (num >> 1);
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return num;
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}
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};
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#endif // PLUGINS_CHANNELTX_MODCHIRPCHAT_CHIRPCHATMODENCODERLORA_H_
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