166 lines
3.1 KiB
C++
166 lines
3.1 KiB
C++
/*
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* Copyright 2007 Free Software Foundation, Inc.
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*
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* This file is part of GNU Radio
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*
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* GNU Radio 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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* GNU Radio 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 GNU Radio; 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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//this is copied almost verbatim from Eric Cottrell's gr-air platform.
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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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/* Mode S Parity Table
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* Index is bit position with bit 0 being the first bit after preamble
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* On short frames an offset of 56 is used.
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*/
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const unsigned int modes_crc_table[112] =
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{
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0x3935ea, // Start of Long Frame CRC
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0x1c9af5,
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0xf1b77e,
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0x78dbbf,
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0xc397db,
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0x9e31e9,
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0xb0e2f0,
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0x587178,
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0x2c38bc,
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0x161c5e,
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0x0b0e2f,
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0xfa7d13,
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0x82c48d,
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0xbe9842,
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0x5f4c21,
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0xd05c14,
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0x682e0a,
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0x341705,
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0xe5f186,
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0x72f8c3,
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0xc68665,
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0x9cb936,
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0x4e5c9b,
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0xd8d449,
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0x939020,
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0x49c810,
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0x24e408,
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0x127204,
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0x093902,
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0x049c81,
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0xfdb444,
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0x7eda22,
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0x3f6d11, // Extended 56 bit field
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0xe04c8c,
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0x702646,
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0x381323,
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0xe3f395,
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0x8e03ce,
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0x4701e7,
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0xdc7af7,
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0x91c77f,
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0xb719bb,
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0xa476d9,
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0xadc168,
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0x56e0b4,
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0x2b705a,
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0x15b82d,
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0xf52612,
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0x7a9309,
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0xc2b380,
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0x6159c0,
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0x30ace0,
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0x185670,
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0x0c2b38,
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0x06159c,
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0x030ace,
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0x018567,
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0xff38b7, // Start of Short Frame CRC
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0x80665f,
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0xbfc92b,
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0xa01e91,
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0xaff54c,
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0x57faa6,
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0x2bfd53,
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0xea04ad,
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0x8af852,
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0x457c29,
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0xdd4410,
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0x6ea208,
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0x375104,
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0x1ba882,
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0x0dd441,
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0xf91024,
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0x7c8812,
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0x3e4409,
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0xe0d800,
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0x706c00,
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0x383600,
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0x1c1b00,
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0x0e0d80,
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0x0706c0,
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0x038360,
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0x01c1b0,
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0x00e0d8,
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0x00706c,
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0x003836,
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0x001c1b,
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0xfff409,
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0x800000, // 24 PI or PA bits
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0x400000,
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0x200000,
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0x100000,
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0x080000,
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0x040000,
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0x020000,
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0x010000,
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0x008000,
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0x004000,
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0x002000,
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0x001000,
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0x000800,
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0x000400,
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0x000200,
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0x000100,
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0x000080,
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0x000040,
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0x000020,
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0x000010,
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0x000008,
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0x000004,
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0x000002,
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0x000001,
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};
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int modes_check_crc(unsigned char data[], int length)
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{
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int crc=0, i;
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for(i = 0; i < length; i++)
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{
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if(data[i/8] & (1 << (7-(i%8))))
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{
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crc ^= modes_crc_table[i+(112-length)];
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}
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}
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return crc;
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}
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