crc8.h

  1/*
  2 * Copyright (c) 2011 Broadcom Corporation
  3 *
  4 * Permission to use, copy, modify, and/or distribute this software for any
  5 * purpose with or without fee is hereby granted, provided that the above
  6 * copyright notice and this permission notice appear in all copies.
  7 *
  8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 11 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 13 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 14 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 15 */
 16#ifndef __CRC8_H_
 17#define __CRC8_H_
 18
 19#include <linux/types.h>
 20
 21/* see usage of this value in crc8() description */
 22#define CRC8_INIT_VALUE		0xFF
 23
 24/*
 25 * Return value of crc8() indicating valid message+crc. This is true
 26 * if a CRC is inverted before transmission. The CRC computed over the
 27 * whole received bitstream is _table[x], where x is the bit pattern
 28 * of the modification (almost always 0xff).
 29 */
 30#define CRC8_GOOD_VALUE(_table)	(_table[0xFF])
 31
 32/* required table size for crc8 algorithm */
 33#define CRC8_TABLE_SIZE			256
 34
 35/* helper macro assuring right table size is used */
 36#define DECLARE_CRC8_TABLE(_table) \
 37	static u8 _table[CRC8_TABLE_SIZE]
 38
 39/**
 40 * crc8_populate_lsb - fill crc table for given polynomial in regular bit order.
 41 *
 42 * @table:	table to be filled.
 43 * @polynomial:	polynomial for which table is to be filled.
 44 *
 45 * This function fills the provided table according the polynomial provided for
 46 * regular bit order (lsb first). Polynomials in CRC algorithms are typically
 47 * represented as shown below.
 48 *
 49 *	poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
 50 *
 51 * For lsb first direction x^7 maps to the lsb. So the polynomial is as below.
 52 *
 53 * - lsb first: poly = 10101011(1) = 0xAB
 54 */
 55void crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
 56
 57/**
 58 * crc8_populate_msb - fill crc table for given polynomial in reverse bit order.
 59 *
 60 * @table:	table to be filled.
 61 * @polynomial:	polynomial for which table is to be filled.
 62 *
 63 * This function fills the provided table according the polynomial provided for
 64 * reverse bit order (msb first). Polynomials in CRC algorithms are typically
 65 * represented as shown below.
 66 *
 67 *	poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
 68 *
 69 * For msb first direction x^7 maps to the msb. So the polynomial is as below.
 70 *
 71 * - msb first: poly = (1)11010101 = 0xD5
 72 */
 73void crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
 74
 75/**
 76 * crc8() - calculate a crc8 over the given input data.
 77 *
 78 * @table:	crc table used for calculation.
 79 * @pdata:	pointer to data buffer.
 80 * @nbytes:	number of bytes in data buffer.
 81 * @crc:	previous returned crc8 value.
 82 *
 83 * The CRC8 is calculated using the polynomial given in crc8_populate_msb()
 84 * or crc8_populate_lsb().
 85 *
 86 * The caller provides the initial value (either %CRC8_INIT_VALUE
 87 * or the previous returned value) to allow for processing of
 88 * discontiguous blocks of data.  When generating the CRC the
 89 * caller is responsible for complementing the final return value
 90 * and inserting it into the byte stream.  When validating a byte
 91 * stream (including CRC8), a final return value of %CRC8_GOOD_VALUE
 92 * indicates the byte stream data can be considered valid.
 93 *
 94 * Reference:
 95 * "A Painless Guide to CRC Error Detection Algorithms", ver 3, Aug 1993
 96 * Williams, Ross N., ross<at>ross.net
 97 * (see URL http://www.ross.net/crc/download/crc_v3.txt).
 98 */
 99u8 crc8(const u8 table[CRC8_TABLE_SIZE], const u8 *pdata, size_t nbytes, u8 crc);
100
101#endif /* __CRC8_H_ */