[网络协议]UDP 计算校验和

1.数据来源

2.实验结果

checksum : 0110100100010010
check the checksum : 1111111111111111

3.C++代码

#include<iostream>
#include<string>

using namespace std;

int n = 14, m = 16;
string a[14] = {
"1001100100010011",
"0000100001101000",
"1010101100000011",
"0000111000001011",
"0000000000010001",
"0000000000001111",
"0000010000111111",
"0000000000001101",
"0000000000001111",
"0000000000000000",
"0101010001000101",
"0101001101010100",
"0100100101001110",
"0100011100000000"
};

int str2int(string s) {
	int res = 0;
	for (auto c : s) {
		res = (res << 1) + c - '0';
	}
	return res;
}

string int2str(int x) {
	string res;
	for (int i = m - 1; i >= 0; i--) {
		if (((x >> i) & 1) == 1)res.push_back('1');
		else res.push_back('0');
	}
	return res;
}

int add(int x, int y) {
	int res = x + y;
	if (((res >> m) & 1) == 1) {
		res -= (1 << m);
		res += 1;
	}
	return res;
}

string get_checksum() {//计算校验和
	int res = 0;
	for (int i = 0; i < n; i++) {
		res = add(res, str2int(a[i]));
	}
	return int2str(~res);
}

string check_checksum() {//校验和的检验
	int res = 0;
	for (int i = 0; i < n; i++) {
		res = add(res, str2int(a[i]));
	}
	return int2str(res);
}

int main() {
	//计算校验和
	string checksum = get_checksum();
	cout <<"checksum : " <<checksum << endl;

	a[9] = checksum;//写入校验和字段
	
	//对校验和进行检验
	cout <<"check the checksum : "<< check_checksum() << endl;

	return 0;
}