64 lines
1.7 KiB
C++
64 lines
1.7 KiB
C++
/*
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* Copyright 2013 Nick Foster
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*
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* This file is part of gr-air-modes
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*
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* gr-air-modes 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, or (at your option)
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* any later version.
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*
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* gr-air-modes 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 gr-air-modes; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <stdio.h>
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#include <gr_air_modes/types.h>
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#include <gr_air_modes/modes_crc.h>
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#include <math.h>
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#include <stdlib.h>
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unsigned int crc_table[256];
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const unsigned int POLY=0xFFF409;
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//generate a bytewise lookup CRC table
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void generate_crc_table(void)
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{
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unsigned int crc = 0;
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for(int n=0; n<256; n++) {
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crc = n<<16;
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for(int k=0; k<8; k++) {
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if(crc & 0x800000) {
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crc = ((crc<<1) ^ POLY) & 0xFFFFFF;
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} else {
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crc = (crc<<1) & 0xFFFFFF;
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}
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}
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crc_table[n] = crc & 0xFFFFFF;
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}
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}
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//Perform a bytewise CRC check
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unsigned int modes_check_crc(unsigned char data[], int length)
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{
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if(crc_table[1] != POLY) generate_crc_table();
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unsigned int crc=0;
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for(int i=0; i<length; i++) {
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crc = crc_table[((crc>>16) ^ data[i]) & 0xff] ^ (crc << 8);
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}
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return crc & 0xFFFFFF;
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}
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