net.h

一个非常强大的库

#define ipsz sizeof(struct iphdr)
#define _isz sizeof(struct icmphdr)
#define _usz sizeof(struct udphdr)
#define _tsz sizeof(struct tcphdr)
#define pssz sizeof(struct pshdr)

unsigned short chck(unsigned short *buff, int size){
	unsigned long cksu = 0;
	while(size > 1){
		cksu += *buff++;
		size -= sizeof(unsigned short);
	}
	if(size)
		cksu += *(unsigned char *)buff;
	cksu = (cksu >> 16) + (cksu & 0xffff);
	cksu += (cksu >> 16);
	return((unsigned short)(~cksu));
}