70 lines
1.8 KiB
C++
70 lines
1.8 KiB
C++
/*
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* Copyright (C) 2018,2020 by Jonathan Naylor G4KLX
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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 2 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, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include "M17CRC.h"
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#include <cstdio>
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#include <cassert>
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const uint8_t BIT_MASK_TABLE1[] = { 0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U };
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#define READ_BIT(p,i) (p[(i)>>3] & BIT_MASK_TABLE1[(i)&7])
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bool CM17CRC::checkCRC(const unsigned char* in, unsigned int nBytes)
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{
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assert(in != NULL);
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assert(nBytes > 2U);
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uint16_t crc = createCRC(in, nBytes);
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uint8_t temp[2U];
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temp[0U] = (crc >> 8) & 0xFFU;
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temp[1U] = (crc >> 0) & 0xFFU;
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return temp[0U] == in[nBytes - 2U] && temp[1U] == in[nBytes - 1U];
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}
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void CM17CRC::encodeCRC(unsigned char* in, unsigned int nBytes)
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{
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assert(in != NULL);
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assert(nBytes > 2U);
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uint16_t crc = createCRC(in, nBytes);
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in[nBytes - 2U] = (crc >> 8) & 0xFFU;
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in[nBytes - 1U] = (crc >> 0) & 0xFFU;
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}
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uint16_t CM17CRC::createCRC(const unsigned char* in, unsigned int nBytes)
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{
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assert(in != NULL);
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uint16_t crc = 0xFFFFU;
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for (unsigned int i = 0U; i < nBytes; i++) {
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bool bit1 = READ_BIT(in, i) != 0x00U;
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bool bit2 = (crc & 0x8000U) == 0x8000U;
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crc <<= 1;
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if (bit1 ^ bit2)
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crc ^= 0x5935U;
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}
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return crc;
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}
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