crc8.c

00001 /***************************************************************************//**
00002  *   @file   crc8.c
00003  *   @brief  Source file of CRC-8 computation.
00004  *   @author Darius Berghe (darius.berghe@analog.com)
00005 ********************************************************************************
00006  * Copyright 2020(c) Analog Devices, Inc.
00007  *
00008  * All rights reserved.
00009  *
00010  * Redistribution and use in source and binary forms, with or without
00011  * modification, are permitted provided that the following conditions are met:
00012  *  - Redistributions of source code must retain the above copyright
00013  *    notice, this list of conditions and the following disclaimer.
00014  *  - Redistributions in binary form must reproduce the above copyright
00015  *    notice, this list of conditions and the following disclaimer in
00016  *    the documentation and/or other materials provided with the
00017  *    distribution.
00018  *  - Neither the name of Analog Devices, Inc. nor the names of its
00019  *    contributors may be used to endorse or promote products derived
00020  *    from this software without specific prior written permission.
00021  *  - The use of this software may or may not infringe the patent rights
00022  *    of one or more patent holders.  This license does not release you
00023  *    from the requirement that you obtain separate licenses from these
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00025  *  - Use of the software either in source or binary form, must be run
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00028  * THIS SOFTWARE IS PROVIDED BY ANALOG DEVICES "AS IS" AND ANY EXPRESS OR
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00037  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00038 *******************************************************************************/
00039 #include "crc8.h"
00040 
00041 /***************************************************************************//**
00042  * @brief Creates the CRC-8 lookup table for a given polynomial.
00043  *
00044  * @param table      - Pointer to a CRC-8 lookup table to write to.
00045  * @param polynomial - msb-first representation of desired polynomial.
00046  *
00047  * Polynomials in CRC algorithms are typically represented as shown below.
00048  *
00049  *  poly = x^8 + x^2 + x^1 + 1
00050  *
00051  * Using msb-first direction, x^7 maps to the msb.
00052  *
00053  *  msb first: poly = (1)00000111 = 0x07
00054  *
00055  * @return None.
00056 *******************************************************************************/
00057 void crc8_populate_msb(uint8_t * table, const uint8_t polynomial)
00058 {
00059     if (!table)
00060         return;
00061 
00062     for (int16_t n = 0; n < CRC8_TABLE_SIZE; n++) {
00063         uint8_t currByte = (uint8_t)n;
00064         for (uint8_t bit = 0; bit < 8; bit++) {
00065             if ((currByte & 0x80) != 0) {
00066                 currByte <<= 1;
00067                 currByte ^= polynomial;
00068             } else {
00069                 currByte <<= 1;
00070             }
00071         }
00072         table[n] = currByte;
00073     }
00074 }
00075 
00076 /***************************************************************************//**
00077  * @brief Computes the CRC-8 over a buffer of data.
00078  *
00079  * @param table     - Pointer to a CRC-8 lookup table for the desired polynomial.
00080  * @param pdata     - Pointer to 8-bit data buffer.
00081  * @param nbytes    - Number of bytes to compute the CRC-8 over.
00082  * @param crc       - Initial value for the CRC-8 computation. Can be used to
00083  *                    cascade calls to this function by providing a previous
00084  *                    output of this function as the crc parameter.
00085  *
00086  * @return crc      - Computed CRC-8 value.
00087 *******************************************************************************/
00088 uint8_t crc8(const uint8_t * table, const uint8_t *pdata, size_t nbytes,
00089          uint8_t crc)
00090 {
00091     unsigned int idx;
00092 
00093     while (nbytes--) {
00094         idx = (crc ^ *pdata);
00095         crc = (table[idx]) & 0xff;
00096         pdata++;
00097     }
00098 
00099     return crc;
00100 }