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  */
  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  */
  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  */
  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");