crc8.h
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/*
* Copyright (c) 2011 Broadcom Corporation
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#ifndef __CRC8_H_
#define __CRC8_H_
#include <linux/types.h>
/* see usage of this value in crc8() description */
#define CRC8_INIT_VALUE 0xFF
/*
* Return value of crc8() indicating valid message+crc. This is true
* if a CRC is inverted before transmission. The CRC computed over the
* whole received bitstream is _table[x], where x is the bit pattern
* of the modification (almost always 0xff).
*/
#define CRC8_GOOD_VALUE(_table) (_table[0xFF])
/* required table size for crc8 algorithm */
#define CRC8_TABLE_SIZE 256
/* helper macro assuring right table size is used */
#define DECLARE_CRC8_TABLE(_table) \
static u8 _table[CRC8_TABLE_SIZE]
/**
* crc8_populate_lsb - fill crc table for given polynomial in regular bit order.
*
* @table: table to be filled.
* @polynomial: polynomial for which table is to be filled.
*
* This function fills the provided table according the polynomial provided for
* regular bit order (lsb first). Polynomials in CRC algorithms are typically
* represented as shown below.
*
* poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
*
* For lsb first direction x^7 maps to the lsb. So the polynomial is as below.
*
* - lsb first: poly = 10101011(1) = 0xAB
*/
void crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
/**
* crc8_populate_msb - fill crc table for given polynomial in reverse bit order.
*
* @table: table to be filled.
* @polynomial: polynomial for which table is to be filled.
*
* This function fills the provided table according the polynomial provided for
* reverse bit order (msb first). Polynomials in CRC algorithms are typically
* represented as shown below.
*
* poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
*
* For msb first direction x^7 maps to the msb. So the polynomial is as below.
*
* - msb first: poly = (1)11010101 = 0xD5
*/
void crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
/**
* crc8() - calculate a crc8 over the given input data.
*
* @table: crc table used for calculation.
* @pdata: pointer to data buffer.
* @nbytes: number of bytes in data buffer.
* @crc: previous returned crc8 value.
*
* The CRC8 is calculated using the polynomial given in crc8_populate_msb()
* or crc8_populate_lsb().
*
* The caller provides the initial value (either %CRC8_INIT_VALUE
* or the previous returned value) to allow for processing of
* discontiguous blocks of data. When generating the CRC the
* caller is responsible for complementing the final return value
* and inserting it into the byte stream. When validating a byte
* stream (including CRC8), a final return value of %CRC8_GOOD_VALUE
* indicates the byte stream data can be considered valid.
*
* Reference:
* "A Painless Guide to CRC Error Detection Algorithms", ver 3, Aug 1993
* Williams, Ross N., ross<at>ross.net
* (see URL http://www.ross.net/crc/download/crc_v3.txt).
*/
u8 crc8(const u8 table[CRC8_TABLE_SIZE], u8 *pdata, size_t nbytes, u8 crc);
#endif /* __CRC8_H_ */