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 */ 55 void 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 */ 73 void 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 */ 99 u8 crc8(const u8 table[CRC8_TABLE_SIZE], const u8 *pdata, size_t nbytes, u8 crc); 100 101 #endif /* __CRC8_H_ */ 102