LXR linux/lib/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/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 */
  29void 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}
  43EXPORT_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 */
  51void 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}
  64EXPORT_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 */
  74u8 crc8(const u8 table[CRC8_TABLE_SIZE], const 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}
  82EXPORT_SYMBOL(crc8);
  83
  84MODULE_DESCRIPTION("CRC8 (by Williams, Ross N.) function");
  85MODULE_AUTHOR("Broadcom Corporation");
  86MODULE_LICENSE("Dual BSD/GPL");
  87