T640_DTU/USER0813/libcrc-2.0/crcccitt.c

/*
 * Library: libcrc
 * File:    src/crcccitt.c
 * Author:  Lammert Bies
 *
 * This file is licensed under the MIT License as stated below
 *
 * Copyright (c) 1999-2016 Lammert Bies
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * Description
 * -----------
 * The module src/crcccitt.c contains routines which are used to calculate the
 * CCITT CRC values of a string of bytes.
 */

#include <stdbool.h>
#include <stdlib.h>
#include "checksum.h"

static uint16_t		crc_ccitt_generic( const unsigned char *input_str, size_t num_bytes, uint16_t start_value );
static void             init_crcccitt_tab( void );

//static bool             crc_tabccitt_init       = false;
//static uint16_t         crc_tabccitt[256];

static const uint16_t   crc_tabccitt[256] =
{
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108, 0x9129,
0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231, 0x0210, 0x3273, 0x2252, 
0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C,
0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672,
0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 
0xF7DF, 0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861,
0x2802, 0x3823, 0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC,
0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5,
0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B,
0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78, 0x9188, 0x81A9, 
0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1, 0x30C2, 0x20E3,
0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C,
0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 
0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3,
0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8,
0xE75F, 0xF77E, 0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676,
0x4615, 0x5634, 0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C, 
0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A, 0x4A75, 0x5A54, 0x6A37, 0x7A16,
0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 
0x9DE8, 0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8, 0x6E17, 0x7E36, 
0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0    
};
/*
 * uint16_t crc_xmodem( const unsigned char *input_str, size_t num_bytes );
 *
 * The function crc_xmodem() performs a one-pass calculation of an X-Modem CRC
 * for a byte string that has been passed as a parameter.
 */

uint16_t crc_xmodem( const unsigned char *input_str, size_t num_bytes ) {

	return crc_ccitt_generic( input_str, num_bytes, CRC_START_XMODEM );

}  /* crc_xmodem */

/*
 * uint16_t crc_ccitt_1d0f( const unsigned char *input_str, size_t num_bytes );
 *
 * The function crc_ccitt_1d0f() performs a one-pass calculation of the CCITT
 * CRC for a byte string that has been passed as a parameter. The initial value
 * 0x1d0f is used for the CRC.
 */

uint16_t crc_ccitt_1d0f( const unsigned char *input_str, size_t num_bytes ) {

	return crc_ccitt_generic( input_str, num_bytes, CRC_START_CCITT_1D0F );

}  /* crc_ccitt_1d0f */

/*
 * uint16_t crc_ccitt_ffff( const unsigned char *input_str, size_t num_bytes );
 *
 * The function crc_ccitt_ffff() performs a one-pass calculation of the CCITT
 * CRC for a byte string that has been passed as a parameter. The initial value
 * 0xffff is used for the CRC.
 */

uint16_t crc_ccitt_ffff( const unsigned char *input_str, size_t num_bytes ) {

	return crc_ccitt_generic( input_str, num_bytes, CRC_START_CCITT_FFFF );

}  /* crc_ccitt_ffff */

/*
 * static uint16_t crc_ccitt_generic( const unsigned char *input_str, size_t num_bytes, uint16_t start_value );
 *
 * The function crc_ccitt_generic() is a generic implementation of the CCITT
 * algorithm for a one-pass calculation of the CRC for a byte string. The
 * function accepts an initial start value for the crc.
 */

static uint16_t crc_ccitt_generic( const unsigned char *input_str, size_t num_bytes, uint16_t start_value ) {

	uint16_t crc;
	uint16_t tmp;
	uint16_t short_c;
	const unsigned char *ptr;
	size_t a;

	//if ( ! crc_tabccitt_init ) init_crcccitt_tab();

	crc = start_value;
	ptr = input_str;

	if ( ptr != NULL ) for (a=0; a<num_bytes; a++) {

		short_c = 0x00ff & (unsigned short) *ptr;
		tmp     = (crc >> 8) ^ short_c;
		crc     = (crc << 8) ^ crc_tabccitt[tmp];

		ptr++;
	}

	return crc;

}  /* crc_ccitt_generic */

/*
 * uint16_t update_crc_ccitt( uint16_t crc, unsigned char c );
 *
 * The function update_crc_ccitt() calculates a new CRC-CCITT value based on
 * the previous value of the CRC and the next byte of the data to be checked.
 */

uint16_t update_crc_ccitt( uint16_t crc, unsigned char c ) {

	int16_t tmp;
	int16_t short_c;

	short_c  = 0x00ff & (uint16_t) c;

	//if ( ! crc_tabccitt_init ) init_crcccitt_tab();

	tmp = (crc >> 8) ^ short_c;
	crc = (crc << 8) ^ crc_tabccitt[tmp];

	return crc;

}  /* update_crc_ccitt */

/*
 * static void init_crcccitt_tab( void );
 *
 * For optimal performance, the routine to calculate the CRC-CCITT uses a
 * lookup table with pre-compiled values that can be directly applied in the
 * XOR action. This table is created at the first call of the function by the
 * init_crcccitt_tab() routine.
 */
/*
static void init_crcccitt_tab( void ) {

	uint16_t i;
	uint16_t j;
	uint16_t crc;
	uint16_t c;

	for (i=0; i<256; i++) {

		crc = 0;
		c   = i << 8;

		for (j=0; j<8; j++) {

			if ( (crc ^ c) & 0x8000 ) crc = ( crc << 1 ) ^ CRC_POLY_CCITT;
			else                      crc =   crc << 1;

			c = c << 1;
		}

		crc_tabccitt[i] = crc;
	}

	crc_tabccitt_init = true;

} 
*/
/* init_crcccitt_tab */