crc8.c

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