#include "Crc.h"
CCrc::CCrc()
{
	BuildTable32();
}

CCrc::~CCrc()
{

}
void CCrc::BuildTable32()
{
	const unsigned long  cnCRC_32=0x04C10DB7L;
	unsigned long i, j;
	unsigned long nData;
	unsigned long nAccum;
	for(i=0;i<256;i++)
	{
		nData=(unsigned long)(i<<24);
		nAccum=0;
		for (j=0;j<8;j++)
		{
			if((nData^nAccum)&0x80000000L) nAccum=(nAccum<<1)^cnCRC_32;
			else nAccum<<=1;
			nData<<=1;
		}
		Table_CRC[(short)i]=nAccum;
	}
}
// 計算32位 CRC-32 值
unsigned long int CCrc::Crc32Mtt(const unsigned char *aData, const unsigned long aSize, unsigned long nAccum)
{
	unsigned long i;
	for(i=0;i<aSize;i++) nAccum=(nAccum<<8) ^ Table_CRC[(short)((nAccum>>24)^*aData++)];
	return nAccum;
}