TOMOYO Linux Cross Reference
Linux/include/linux/crc8.h

   /*
    * Copyright (c) 2011 Broadcom Corporation
    *
    * Permission to use, copy, modify, and/or distribute this software for any
    * purpose with or without fee is hereby granted, provided that the above
    * copyright notice and this permission notice appear in all copies.
    *
    * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
   * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
   * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
   * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  #ifndef __CRC8_H_
  #define __CRC8_H_
  
  #include <linux/types.h>
  
  /* see usage of this value in crc8() description */
  #define CRC8_INIT_VALUE         0xFF
  
  /*
   * Return value of crc8() indicating valid message+crc. This is true
   * if a CRC is inverted before transmission. The CRC computed over the
   * whole received bitstream is _table[x], where x is the bit pattern
   * of the modification (almost always 0xff).
   */
  #define CRC8_GOOD_VALUE(_table) (_table[0xFF])
  
  /* required table size for crc8 algorithm */
  #define CRC8_TABLE_SIZE                 256
  
  /* helper macro assuring right table size is used */
  #define DECLARE_CRC8_TABLE(_table) \
          static u8 _table[CRC8_TABLE_SIZE]
  
  /**
   * crc8_populate_lsb - fill crc table for given polynomial in regular bit order.
   *
   * @table:      table to be filled.
   * @polynomial: polynomial for which table is to be filled.
   *
   * This function fills the provided table according the polynomial provided for
   * regular bit order (lsb first). Polynomials in CRC algorithms are typically
   * represented as shown below.
   *
   *      poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
   *
   * For lsb first direction x^7 maps to the lsb. So the polynomial is as below.
   *
   * - lsb first: poly = 10101011(1) = 0xAB
   */
  void crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
  
  /**
   * crc8_populate_msb - fill crc table for given polynomial in reverse bit order.
   *
   * @table:      table to be filled.
   * @polynomial: polynomial for which table is to be filled.
   *
   * This function fills the provided table according the polynomial provided for
   * reverse bit order (msb first). Polynomials in CRC algorithms are typically
   * represented as shown below.
   *
   *      poly = x^8 + x^7 + x^6 + x^4 + x^2 + 1
   *
   * For msb first direction x^7 maps to the msb. So the polynomial is as below.
   *
   * - msb first: poly = (1)11010101 = 0xD5
   */
  void crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial);
  
  /**
   * crc8() - calculate a crc8 over the given input data.
   *
   * @table:      crc table used for calculation.
   * @pdata:      pointer to data buffer.
   * @nbytes:     number of bytes in data buffer.
   * @crc:        previous returned crc8 value.
   *
   * The CRC8 is calculated using the polynomial given in crc8_populate_msb()
   * or crc8_populate_lsb().
   *
   * The caller provides the initial value (either %CRC8_INIT_VALUE
   * or the previous returned value) to allow for processing of
   * discontiguous blocks of data.  When generating the CRC the
   * caller is responsible for complementing the final return value
   * and inserting it into the byte stream.  When validating a byte
   * stream (including CRC8), a final return value of %CRC8_GOOD_VALUE
   * indicates the byte stream data can be considered valid.
   *
   * Reference:
   * "A Painless Guide to CRC Error Detection Algorithms", ver 3, Aug 1993
   * Williams, Ross N., ross<at>ross.net
   * (see URL http://www.ross.net/crc/download/crc_v3.txt).
   */
  u8 crc8(const u8 table[CRC8_TABLE_SIZE], const u8 *pdata, size_t nbytes, u8 crc);
 
 #endif /* __CRC8_H_ */
 

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