Remote Access Control

crc.c

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// This file has been prepared for Doxygen automatic documentation generation.
#include "crc.h"
#include "common.h"
#include "config.h"



byte CRCReg[3];



void initCRC(void)
{
        CRCReg[0] = 0xff;
        CRCReg[1] = 0xff;
        CRCReg[2] = 0x00; // Always 0x00. See comment in crc.h file.
}



void calcCRC( byte nextByte )
{
        byte reg0 = CRCReg[0];
        byte reg1 = CRCReg[1];
        byte tempByte = nextByte;
        byte count = 8;
        do {
                if( reg0 >> 7 ) {
                        reg0 = (reg0 << 1) | (reg1 >> 7);
                        reg1 = (reg1 << 1) | (tempByte >> 7);
                        tempByte <<= 1;

                        reg0 ^= CRC_POLY >> 8;
                        reg1 ^= CRC_POLY & 0xff;
                } else {
                        reg0 = (reg0 << 1) | (reg1 >> 7);
                        reg1 = (reg1 << 1) | (tempByte >> 7);
                        tempByte <<= 1;
                }
        } while( --count );

        CRCReg[0] = reg0;
        CRCReg[1] = reg1;
}