网友张巍提供的tcpip协议栈,是一个成功稳定的以太网接口上的TCP/IP协议程序。里面包括有说明

				/* 16 bit CRC-CCITT stuff. Extracted from Bill Simpson's PPP */
				
				#define FCS_START	0xffff	/* Starting bit string for FCS calculation */
				#define FCS_FINAL	0xf0b8	/* FCS when summed over frame and sender FCS */
				
				#define FCS(fcs, c)		(((fcs) >> 8) ^ Fcstab[((fcs) ^ (c)) & 0x00ff])
				
				extern unsigned short Fcstab[];
				int crc_check(unsigned char *buf,unsigned int len);
				void crc_gen(unsigned char *buf,unsigned int len);