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e18baa7cc3
crc8() does not change the data passed to it, so the pointer argument should be declared const. This avoids callers that receive const data having to cast it to a non-const pointer to call crc8(). Link: https://lkml.kernel.org/r/20210329122409.3291-1-rf@opensource.cirrus.com Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com> Acked-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
102 lines
3.7 KiB
C
102 lines
3.7 KiB
C
/*
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* Copyright (c) 2011 Broadcom Corporation
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#ifndef __CRC8_H_
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#define __CRC8_H_
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#include <linux/types.h>
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/* see usage of this value in crc8() description */
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#define CRC8_INIT_VALUE 0xFF
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/*
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* Return value of crc8() indicating valid message+crc. This is true
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* if a CRC is inverted before transmission. The CRC computed over the
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* whole received bitstream is _table[x], where x is the bit pattern
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* of the modification (almost always 0xff).
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*/
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#define CRC8_GOOD_VALUE(_table) (_table[0xFF])
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/* required table size for crc8 algorithm */
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#define CRC8_TABLE_SIZE 256
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/* helper macro assuring right table size is used */
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#define DECLARE_CRC8_TABLE(_table) \
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static u8 _table[CRC8_TABLE_SIZE]
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/**
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* crc8_populate_lsb - fill crc table for given polynomial in regular bit order.
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*
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* @table: table to be filled.
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* @polynomial: polynomial for which table is to be filled.
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*
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* This function fills the provided table according the polynomial provided for
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* regular bit order (lsb first). Polynomials in CRC algorithms are typically
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* represented as shown below.
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*
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* poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
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*
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* For lsb first direction x^7 maps to the lsb. So the polynomial is as below.
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*
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* - lsb first: poly = 10101011(1) = 0xAB
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*/
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void crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
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/**
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* crc8_populate_msb - fill crc table for given polynomial in reverse bit order.
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*
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* @table: table to be filled.
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* @polynomial: polynomial for which table is to be filled.
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*
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* This function fills the provided table according the polynomial provided for
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* reverse bit order (msb first). Polynomials in CRC algorithms are typically
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* represented as shown below.
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*
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* poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
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*
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* For msb first direction x^7 maps to the msb. So the polynomial is as below.
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*
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* - msb first: poly = (1)11010101 = 0xD5
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*/
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void crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
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/**
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* crc8() - calculate a crc8 over the given input data.
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*
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* @table: crc table used for calculation.
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* @pdata: pointer to data buffer.
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* @nbytes: number of bytes in data buffer.
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* @crc: previous returned crc8 value.
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*
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* The CRC8 is calculated using the polynomial given in crc8_populate_msb()
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* or crc8_populate_lsb().
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*
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* The caller provides the initial value (either %CRC8_INIT_VALUE
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* or the previous returned value) to allow for processing of
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* discontiguous blocks of data. When generating the CRC the
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* caller is responsible for complementing the final return value
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* and inserting it into the byte stream. When validating a byte
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* stream (including CRC8), a final return value of %CRC8_GOOD_VALUE
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* indicates the byte stream data can be considered valid.
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*
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* Reference:
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* "A Painless Guide to CRC Error Detection Algorithms", ver 3, Aug 1993
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* Williams, Ross N., ross<at>ross.net
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* (see URL http://www.ross.net/crc/download/crc_v3.txt).
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*/
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u8 crc8(const u8 table[CRC8_TABLE_SIZE], const u8 *pdata, size_t nbytes, u8 crc);
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#endif /* __CRC8_H_ */
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