/*
 * Copyright (c) 2015 Maurizio Lombardi
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @file crc16_ibm.c
 *
 * Implementation of CRC16-IBM (polynomial = 0xA001)
 *
 */

#include "crypto.h"

static const uint16_t crct[256] = {
	0x0000,	0xc0c1,	0xc181,	0x0140,	0xc301,	0x03c0,	0x0280,	0xc241,
	0xc601,	0x06c0,	0x0780,	0xc741,	0x0500,	0xc5c1,	0xc481,	0x0440,
	0xcc01,	0x0cc0,	0x0d80,	0xcd41,	0x0f00,	0xcfc1,	0xce81,	0x0e40,
	0x0a00,	0xcac1,	0xcb81,	0x0b40,	0xc901,	0x09c0,	0x0880,	0xc841,
	0xd801,	0x18c0,	0x1980,	0xd941,	0x1b00,	0xdbc1,	0xda81,	0x1a40,
	0x1e00,	0xdec1,	0xdf81,	0x1f40,	0xdd01,	0x1dc0,	0x1c80,	0xdc41,
	0x1400,	0xd4c1,	0xd581,	0x1540,	0xd701,	0x17c0,	0x1680,	0xd641,
	0xd201,	0x12c0,	0x1380,	0xd341,	0x1100,	0xd1c1,	0xd081,	0x1040,
	0xf001,	0x30c0,	0x3180,	0xf141,	0x3300,	0xf3c1,	0xf281,	0x3240,
	0x3600,	0xf6c1,	0xf781,	0x3740,	0xf501,	0x35c0,	0x3480,	0xf441,
	0x3c00,	0xfcc1,	0xfd81,	0x3d40,	0xff01,	0x3fc0,	0x3e80,	0xfe41,
	0xfa01,	0x3ac0,	0x3b80,	0xfb41,	0x3900,	0xf9c1,	0xf881,	0x3840,
	0x2800,	0xe8c1,	0xe981,	0x2940,	0xeb01,	0x2bc0,	0x2a80,	0xea41,
	0xee01,	0x2ec0,	0x2f80,	0xef41,	0x2d00,	0xedc1,	0xec81,	0x2c40,
	0xe401,	0x24c0,	0x2580,	0xe541,	0x2700,	0xe7c1,	0xe681,	0x2640,
	0x2200,	0xe2c1,	0xe381,	0x2340,	0xe101,	0x21c0,	0x2080,	0xe041,
	0xa001,	0x60c0,	0x6180,	0xa141,	0x6300,	0xa3c1,	0xa281,	0x6240,
	0x6600,	0xa6c1,	0xa781,	0x6740,	0xa501,	0x65c0,	0x6480,	0xa441,
	0x6c00,	0xacc1,	0xad81,	0x6d40,	0xaf01,	0x6fc0,	0x6e80,	0xae41,
	0xaa01,	0x6ac0,	0x6b80,	0xab41,	0x6900,	0xa9c1,	0xa881,	0x6840,
	0x7800,	0xb8c1,	0xb981,	0x7940,	0xbb01,	0x7bc0,	0x7a80,	0xba41,
	0xbe01,	0x7ec0,	0x7f80,	0xbf41,	0x7d00,	0xbdc1,	0xbc81,	0x7c40,
	0xb401,	0x74c0,	0x7580,	0xb541,	0x7700,	0xb7c1,	0xb681,	0x7640,
	0x7200,	0xb2c1,	0xb381,	0x7340,	0xb101,	0x71c0,	0x7080,	0xb041,
	0x5000,	0x90c1,	0x9181,	0x5140,	0x9301,	0x53c0,	0x5280,	0x9241,
	0x9601,	0x56c0,	0x5780,	0x9741,	0x5500,	0x95c1,	0x9481,	0x5440,
	0x9c01,	0x5cc0,	0x5d80,	0x9d41,	0x5f00,	0x9fc1,	0x9e81,	0x5e40,
	0x5a00,	0x9ac1,	0x9b81,	0x5b40,	0x9901,	0x59c0,	0x5880,	0x9841,
	0x8801,	0x48c0,	0x4980,	0x8941,	0x4b00,	0x8bc1,	0x8a81,	0x4a40,
	0x4e00,	0x8ec1,	0x8f81,	0x4f40,	0x8d01,	0x4dc0,	0x4c80,	0x8c41,
	0x4400,	0x84c1,	0x8581,	0x4540,	0x8701,	0x47c0,	0x4680,	0x8641,
	0x8201,	0x42c0,	0x4380,	0x8341,	0x4100,	0x81c1,	0x8081,	0x4040
};

/* Compute a CRC16
 *
 * @param crc    Init value of the CRC
 * @param buf    Pointer to the data
 * @param len    Size of the buffer
 *
 * @return       Value of the CRC.
 */
uint16_t crc16_ibm(uint16_t crc, uint8_t *buf, size_t len)
{
	while (len--) {
		crc ^= *buf++;
		crc = (crc >> 8) ^ crct[crc & 0x00FF];
	}

	return crc;
}