1*4882a593Smuzhiyun /* 2*4882a593Smuzhiyun * Copyright (c) 2011 Broadcom Corporation 3*4882a593Smuzhiyun * 4*4882a593Smuzhiyun * Permission to use, copy, modify, and/or distribute this software for any 5*4882a593Smuzhiyun * purpose with or without fee is hereby granted, provided that the above 6*4882a593Smuzhiyun * copyright notice and this permission notice appear in all copies. 7*4882a593Smuzhiyun * 8*4882a593Smuzhiyun * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 9*4882a593Smuzhiyun * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 10*4882a593Smuzhiyun * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 11*4882a593Smuzhiyun * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 12*4882a593Smuzhiyun * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 13*4882a593Smuzhiyun * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 14*4882a593Smuzhiyun * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 15*4882a593Smuzhiyun */ 16*4882a593Smuzhiyun #ifndef __CRC8_H_ 17*4882a593Smuzhiyun #define __CRC8_H_ 18*4882a593Smuzhiyun 19*4882a593Smuzhiyun #include <linux/types.h> 20*4882a593Smuzhiyun 21*4882a593Smuzhiyun /* see usage of this value in crc8() description */ 22*4882a593Smuzhiyun #define CRC8_INIT_VALUE 0xFF 23*4882a593Smuzhiyun 24*4882a593Smuzhiyun /* 25*4882a593Smuzhiyun * Return value of crc8() indicating valid message+crc. This is true 26*4882a593Smuzhiyun * if a CRC is inverted before transmission. The CRC computed over the 27*4882a593Smuzhiyun * whole received bitstream is _table[x], where x is the bit pattern 28*4882a593Smuzhiyun * of the modification (almost always 0xff). 29*4882a593Smuzhiyun */ 30*4882a593Smuzhiyun #define CRC8_GOOD_VALUE(_table) (_table[0xFF]) 31*4882a593Smuzhiyun 32*4882a593Smuzhiyun /* required table size for crc8 algorithm */ 33*4882a593Smuzhiyun #define CRC8_TABLE_SIZE 256 34*4882a593Smuzhiyun 35*4882a593Smuzhiyun /* helper macro assuring right table size is used */ 36*4882a593Smuzhiyun #define DECLARE_CRC8_TABLE(_table) \ 37*4882a593Smuzhiyun static u8 _table[CRC8_TABLE_SIZE] 38*4882a593Smuzhiyun 39*4882a593Smuzhiyun /** 40*4882a593Smuzhiyun * crc8_populate_lsb - fill crc table for given polynomial in regular bit order. 41*4882a593Smuzhiyun * 42*4882a593Smuzhiyun * @table: table to be filled. 43*4882a593Smuzhiyun * @polynomial: polynomial for which table is to be filled. 44*4882a593Smuzhiyun * 45*4882a593Smuzhiyun * This function fills the provided table according the polynomial provided for 46*4882a593Smuzhiyun * regular bit order (lsb first). Polynomials in CRC algorithms are typically 47*4882a593Smuzhiyun * represented as shown below. 48*4882a593Smuzhiyun * 49*4882a593Smuzhiyun * poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1 50*4882a593Smuzhiyun * 51*4882a593Smuzhiyun * For lsb first direction x^7 maps to the lsb. So the polynomial is as below. 52*4882a593Smuzhiyun * 53*4882a593Smuzhiyun * - lsb first: poly = 10101011(1) = 0xAB 54*4882a593Smuzhiyun */ 55*4882a593Smuzhiyun void crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial); 56*4882a593Smuzhiyun 57*4882a593Smuzhiyun /** 58*4882a593Smuzhiyun * crc8_populate_msb - fill crc table for given polynomial in reverse bit order. 59*4882a593Smuzhiyun * 60*4882a593Smuzhiyun * @table: table to be filled. 61*4882a593Smuzhiyun * @polynomial: polynomial for which table is to be filled. 62*4882a593Smuzhiyun * 63*4882a593Smuzhiyun * This function fills the provided table according the polynomial provided for 64*4882a593Smuzhiyun * reverse bit order (msb first). Polynomials in CRC algorithms are typically 65*4882a593Smuzhiyun * represented as shown below. 66*4882a593Smuzhiyun * 67*4882a593Smuzhiyun * poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1 68*4882a593Smuzhiyun * 69*4882a593Smuzhiyun * For msb first direction x^7 maps to the msb. So the polynomial is as below. 70*4882a593Smuzhiyun * 71*4882a593Smuzhiyun * - msb first: poly = (1)11010101 = 0xD5 72*4882a593Smuzhiyun */ 73*4882a593Smuzhiyun void crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial); 74*4882a593Smuzhiyun 75*4882a593Smuzhiyun /** 76*4882a593Smuzhiyun * crc8() - calculate a crc8 over the given input data. 77*4882a593Smuzhiyun * 78*4882a593Smuzhiyun * @table: crc table used for calculation. 79*4882a593Smuzhiyun * @pdata: pointer to data buffer. 80*4882a593Smuzhiyun * @nbytes: number of bytes in data buffer. 81*4882a593Smuzhiyun * @crc: previous returned crc8 value. 82*4882a593Smuzhiyun * 83*4882a593Smuzhiyun * The CRC8 is calculated using the polynomial given in crc8_populate_msb() 84*4882a593Smuzhiyun * or crc8_populate_lsb(). 85*4882a593Smuzhiyun * 86*4882a593Smuzhiyun * The caller provides the initial value (either %CRC8_INIT_VALUE 87*4882a593Smuzhiyun * or the previous returned value) to allow for processing of 88*4882a593Smuzhiyun * discontiguous blocks of data. When generating the CRC the 89*4882a593Smuzhiyun * caller is responsible for complementing the final return value 90*4882a593Smuzhiyun * and inserting it into the byte stream. When validating a byte 91*4882a593Smuzhiyun * stream (including CRC8), a final return value of %CRC8_GOOD_VALUE 92*4882a593Smuzhiyun * indicates the byte stream data can be considered valid. 93*4882a593Smuzhiyun * 94*4882a593Smuzhiyun * Reference: 95*4882a593Smuzhiyun * "A Painless Guide to CRC Error Detection Algorithms", ver 3, Aug 1993 96*4882a593Smuzhiyun * Williams, Ross N., ross<at>ross.net 97*4882a593Smuzhiyun * (see URL http://www.ross.net/crc/download/crc_v3.txt). 98*4882a593Smuzhiyun */ 99*4882a593Smuzhiyun u8 crc8(const u8 table[CRC8_TABLE_SIZE], u8 *pdata, size_t nbytes, u8 crc); 100*4882a593Smuzhiyun 101*4882a593Smuzhiyun #endif /* __CRC8_H_ */ 102