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/*
* Copyright 2013 Nick Foster
*
* This file is part of gr-air-modes
*
* gr-air-modes is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* gr-air-modes is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with gr-air-modes; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <stdio.h>
#include <air_modes/types.h>
#include <air_modes/modes_crc.h>
#include <math.h>
#include <stdlib.h>
unsigned int crc_table[256];
const unsigned int POLY=0xFFF409;
//generate a bytewise lookup CRC table
void generate_crc_table(void)
{
unsigned int crc = 0;
for(int n=0; n<256; n++) {
crc = n<<16;
for(int k=0; k<8; k++) {
if(crc & 0x800000) {
crc = ((crc<<1) ^ POLY) & 0xFFFFFF;
} else {
crc = (crc<<1) & 0xFFFFFF;
}
}
crc_table[n] = crc & 0xFFFFFF;
}
}
//Perform a bytewise CRC check
unsigned int modes_check_crc(unsigned char data[], int length)
{
if(crc_table[1] != POLY) generate_crc_table();
unsigned int crc=0;
for(int i=0; i<length; i++) {
crc = crc_table[((crc>>16) ^ data[i]) & 0xff] ^ (crc << 8);
}
return crc & 0xFFFFFF;
}
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