crc32.cpp

来自「基于DES加密算法」· C++ 代码 · 共 50 行

//file name:  crc32.cpp
// the implemention of the class CCRC32, which is used to
// calculate the 32-bits CRC of a block memory

// see head file for more infor
//Noted by Sinmin ([e-mail]) July 8,2000


//constructor, do initialize the calss:
// calculate the  crc table

#include "crc32.h"

CCRC32::CCRC32()
{
	m_CRC=0xffffffff;
	initializeCRC32();
}

void CCRC32::initializeCRC32(void)	// initialize, calculate table
{
	int i, j;
	unsigned int r;

	for (i = 0; i < TABLE_SIZE; i++){
        for (r=i,j = BYTE_LENGTH; j > 0; j--){
            if (r & 1)
                r = (r >> 1) ^ CRC32_POLYNOMIAL;
            else
                r >>= 1;
        }
        Table[i] = r;
    }
}

unsigned int CCRC32::calculateCRC(void *pMem,unsigned int byteSize)
{
	unsigned int i;
	char *pD;
	pD=(char *) pMem;
	for(i=0;i<byteSize;i++)
		m_CRC=Table[(m_CRC^(*(pD+i)))&0xff] ^ (m_CRC>>BYTE_LENGTH);
	return m_CRC;
}

void CCRC32::resetCRC(void)
{
	m_CRC=0xffffffff;
}