crc.cpp

00001 /** crc.cpp
00002  *
00003  * @license
00004  * MIT License
00005  *
00006  * Copyright (c) 2016 Andrew D Lindsay/Thing Innovations https://thinginnovations.uk
00007  * 
00008  * Permission is hereby granted, free of charge, to any person obtaining a copy
00009  * of this software and associated documentation files (the "Software"), to deal
00010  * in the Software without restriction, including without limitation the rights
00011  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00012  * copies of the Software, and to permit persons to whom the Software is
00013  * furnished to do so, subject to the following conditions:
00014  * 
00015  * The above copyright notice and this permission notice shall be included in all
00016  * copies or substantial portions of the Software.
00017  * 
00018  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00019  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00020  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00021  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00022  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00023  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
00024  * SOFTWARE.
00025  * 
00026  */
00027 #define CRC32_POLYNOMIAL 0xEDB88320L
00028 
00029 void CRC32Value(unsigned long &CRCval, unsigned char c)
00030 {
00031     /////////////////////////////////////////////////////////////////////////////////////
00032     //CRC must be initialized as zero 
00033     //c is a character from the sequence that is used to form the CRC
00034     //this code is a modification of the code from the Novatel OEM615 specification
00035     /////////////////////////////////////////////////////////////////////////////////////
00036     unsigned long ulTemp1 = ( CRCval >> 8 ) & 0x00FFFFFFL;
00037     unsigned long ulCRC = ((int) CRCval ^ c ) & 0xff ;
00038     for (int  j = 8 ; j > 0; j-- )
00039     {
00040         if ( ulCRC & 1 )
00041         {
00042             ulCRC = ( ulCRC >> 1 ) ^ CRC32_POLYNOMIAL;
00043         }
00044         else
00045         {
00046             ulCRC >>= 1;
00047         }
00048     }
00049     CRCval = ulTemp1 ^ ulCRC;
00050 } 
00051 
00052 /* --------------------------------------------------------------------------
00053 Calculates the CRC-32 of a block of data all at once
00054 //the CRC is from the complete message (header plus data) 
00055 //but excluding (of course) the CRC at the end
00056 -------------------------------------------------------------------------- */
00057 unsigned long CalculateBlockCRC32(
00058         unsigned long ulCount,    /* Number of bytes in the data block */
00059         unsigned char *ucBuffer ) /* Data block */
00060 {
00061     //////////////////////////////////////////////////////////////////////
00062     //the below code tests the CRC32Value procedure used in a markov form
00063     //////////////////////////////////////////////////////////////////////
00064     unsigned long CRC = 0;
00065     for (int i = 0; i<ulCount; i++)
00066     {
00067         CRC32Value( CRC, *ucBuffer++ );
00068     }
00069     return  CRC;
00070 }
00071 
00072 /*
00073 unsigned long CalculateBlockCRC32(
00074         unsigned long ulCount, 
00075         unsigned char *ucBuffer )
00076 {
00077 ////////////////////////////////////////////
00078 //original code from the OEM615 manual
00079 ////////////////////////////////////////////
00080     unsigned long ulTemp1;
00081     unsigned long ulTemp2;
00082     unsigned long ulCRC = 0;
00083     while ( ulCount-- != 0 )
00084     {
00085         ulTemp1 = ( ulCRC >> 8 ) & 0x00FFFFFFL;
00086         ulTemp2 = CRC32Value( ((int) ulCRC ^ *ucBuffer++ ) & 0xff );
00087         ulCRC = ulTemp1 ^ ulTemp2;
00088     }
00089     return( ulCRC );
00090 }
00091 */