static unsigned long crctable[256];
static unsigned char crcinvtable[256];

void init_crc(void)
{
	unsigned long poly = 0xedb88320, value, idx, i;
	
	for (idx = 0 ; idx < 256 ; idx++) {
		for (value = idx, i = 0 ; i < 8 ; i++) {
			if (value & 1) {
				value >>= 1;
				value ^= poly;
			} else {
				value >>= 1;
			}
		}
		crctable[idx] = value;
		crcinvtable[value >> 24] = idx & 0xff;
	}
}

static inline unsigned long iter_crc(unsigned long crc, unsigned char chr)
{
	return (crc >> 8) ^ crctable[chr ^ (crc & 255)];
}

unsigned long calc_crc(unsigned char *buf, unsigned long buflen, unsigned long crc)
{
	while (buflen--)
		crc = iter_crc(crc, *buf++);
	return ~crc;
}