计算UDP校验和的代码如下：

def do_checksum(self, source_string): """ Verify the packet interitity """ sum = 0 max_count = (len(source_string) / 2) * 2 count = 0 while count < max_count:     val = ord(source_string[count + 1]) * 256 + ord(source_string[count])     sum = sum + val     sum = sum & 0xffffffff     count = count + 2  if max_count < len(source_string):     sum = sum + ord(source_string[len(source_string) - 1])     sum = sum & 0xffffffff  sum = (sum >> 16) + (sum & 0xffff) sum = sum + (sum >> 16) answer = ~sum answer = answer & 0xffff answer = answer >> 8 | (answer << 8 & 0xff00) return answer 

UDP的校验和在计算时遇到的任何溢出都会被回卷，那么问题来了：sum = sum & 0xffffffff这条语句应该是直接把溢出舍去了？

所以这段代码对么。。。