计算ICMP头的校验和：

计算ICMP头的校验和：

USHORT checksum(USHORT* buff, int nSize){unsigned long cksum=0;//将数据以字为单位加到cksumwhile (nSize > 1){cksum += *buff++;nSize -= sizeof(USHORT);}//如果为奇数, 将最后一个字扩展到双字，再累加if (nSize){cksum += *(UCHAR*)buff;}//将cksum的高16位与低16位相加，取反后得到校验和cksum = (cksum>>16) + (cksum&&0xffff);cksum += (cksum>>16);return (USHORT)(~cksum);}