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 | |