const int order = 16;
const unsigned long polynom = 0x1021;
const int direct = 1;
const unsigned long crcinit = 0xffff;
const unsigned long crcxor = 0xffff;
const int refin = 1;
const int refout = 1;

unsigned long crcmask;
unsigned long crchighbit;
unsigned long crcinit_direct;
unsigned long crcinit_nondirect;

unsigned char string[] = {0xFF,0x01,0x15,0x11,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
                          0x00};


unsigned long reflect (unsigned long crc, int bitnum) 
{

	// reflects the lower 'bitnum' bits of 'crc'

	unsigned long i, j=1, crcout=0;

	for (i=(unsigned long)1<<(bitnum-1); i; i>>=1) {
		if (crc & i) crcout|=j;
		j<<= 1;
	}
	return (crcout);
}

unsigned long crcbitbybit(unsigned char* p, unsigned long len) 
{
	unsigned long i, j, c, bit;
	unsigned long crc = crcinit_nondirect;

	for (i=0; i<len; i++) {

		c = (unsigned long)*p++;
		if (refin) c = reflect(c, 8);

		for (j=0x80; j; j>>=1) {

			bit = crc & crchighbit;
			crc<<= 1;
			if (c & j) crc|= 1;
			if (bit) crc^= polynom;
		}
	}	

	for (i=0; i<order; i++) {

		bit = crc & crchighbit;
		crc<<= 1;
		if (bit) crc^= polynom;
	}

	if (refout) crc=reflect(crc, order);
	crc^= crcxor;
	crc&= crcmask;

	return(crc);
}

void main(void)
{
	int crc_wert;

	int i;
	unsigned long bit, crc;

	// at first, compute constant bit masks for whole CRC and CRC high bit

	crcmask = ((((unsigned long)1<<(order-1))-1)<<1)|1;
	crchighbit = (unsigned long)1<<(order-1);

	// compute missing initial CRC value

	if (!direct) {

		crcinit_nondirect = crcinit;
		crc = crcinit;
		for (i=0; i<order; i++) {

			bit = crc & crchighbit;
			crc<<= 1;
			if (bit) crc^= polynom;
		}
		crc&= crcmask;
		crcinit_direct = crc;
	}

	else 
	{
		crcinit_direct = crcinit;
		crc = crcinit;
		for (i=0; i<order; i++) 
		{

			bit = crc & 1;
			if (bit) crc^= polynom;
			crc >>= 1;
			if (bit) crc|= crchighbit;
		}	
		crcinit_nondirect = crc;
	}
	crc_wert = crcbitbybit((unsigned char *)string, strlen(string));

	printf("\n\ncrc_wert:0x%x",crc_wert);
}