cksum.c

我自己写的一个tcp/ip的代码

unsigned int cksum(unsigned char * input, unsigned int len)
{
	unsigned long sum;
	unsigned int i;
	unsigned int * ptr; 
	sum = 0;
	ptr=(unsigned int *)input;
	for(i=0; i<(len)/2; i++)
	{
		sum+=*ptr++;
	}
	if(len & 0x01)//表示长度为单数
	{
		sum=sum+((*ptr)&0xff00);
	}
	sum=(sum&0xffff)+((sum>>16)&0xffff);//高16位和低16位相加
	if(sum & 0xffff0000)
	{//表示有进位
		sum++;
	}
	return ((unsigned int)((sum)&0xffff));
}