forked from mirrors/linux
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>
101 lines
3.7 KiB
C
101 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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