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 
17 #define pr_fmt(fmt)		KBUILD_MODNAME ": " fmt
18 
19 #include <linux/module.h>
20 #include <linux/crc8.h>
21 #include <linux/printk.h>
22 
23 /**
24  * crc8_populate_msb - fill crc table for given polynomial in reverse bit order.
25  *
26  * @table:	table to be filled.
27  * @polynomial:	polynomial for which table is to be filled.
28  */
crc8_populate_msb(u8 table[CRC8_TABLE_SIZE],u8 polynomial)29 void crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial)
30 {
31 	int i, j;
32 	const u8 msbit = 0x80;
33 	u8 t = msbit;
34 
35 	table[0] = 0;
36 
37 	for (i = 1; i < CRC8_TABLE_SIZE; i *= 2) {
38 		t = (t << 1) ^ (t & msbit ? polynomial : 0);
39 		for (j = 0; j < i; j++)
40 			table[i+j] = table[j] ^ t;
41 	}
42 }
43 EXPORT_SYMBOL(crc8_populate_msb);
44 
45 /**
46  * crc8_populate_lsb - fill crc table for given polynomial in regular bit order.
47  *
48  * @table:	table to be filled.
49  * @polynomial:	polynomial for which table is to be filled.
50  */
crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE],u8 polynomial)51 void crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial)
52 {
53 	int i, j;
54 	u8 t = 1;
55 
56 	table[0] = 0;
57 
58 	for (i = (CRC8_TABLE_SIZE >> 1); i; i >>= 1) {
59 		t = (t >> 1) ^ (t & 1 ? polynomial : 0);
60 		for (j = 0; j < CRC8_TABLE_SIZE; j += 2*i)
61 			table[i+j] = table[j] ^ t;
62 	}
63 }
64 EXPORT_SYMBOL(crc8_populate_lsb);
65 
66 /**
67  * crc8 - calculate a crc8 over the given input data.
68  *
69  * @table: crc table used for calculation.
70  * @pdata: pointer to data buffer.
71  * @nbytes: number of bytes in data buffer.
72  * @crc: previous returned crc8 value.
73  */
crc8(const u8 table[CRC8_TABLE_SIZE],u8 * pdata,size_t nbytes,u8 crc)74 u8 crc8(const u8 table[CRC8_TABLE_SIZE], u8 *pdata, size_t nbytes, u8 crc)
75 {
76 	/* loop over the buffer data */
77 	while (nbytes-- > 0)
78 		crc = table[(crc ^ *pdata++) & 0xff];
79 
80 	return crc;
81 }
82 EXPORT_SYMBOL(crc8);
83 
84 MODULE_DESCRIPTION("CRC8 (by Williams, Ross N.) function");
85 MODULE_AUTHOR("Broadcom Corporation");
86 MODULE_LICENSE("Dual BSD/GPL");
87