CRC.cpp

#include <bits/stdc++.h>
using namespace std;

string xor1(string a, string b)
{
    string result = "";
    int n = b.length();
    for (int i = 1; i < n; i++)
    {
        if (a[i] == b[i])
            result += "0";
        else
            result += "1";
    }
    return result;
}
string mod2div(string dividend, string divisor)
{
    int pick = divisor.length();
    string tmp = dividend.substr(0, pick);
    int n = dividend.length();
    while (pick < n)
    {
        if (tmp[0] == '1')
            tmp = xor1(divisor, tmp) + dividend[pick];
        else
            tmp = xor1(std::string(pick, '0'), tmp) + dividend[pick];
        pick += 1;
    }
    if (tmp[0] == '1')
        tmp = xor1(divisor, tmp);
    else
        tmp = xor1(std::string(pick, '0'), tmp);
    return tmp;
}
void encodeData(string data, string key)
{
    int l_key = key.length();
    string appended_data = (data + std::string(l_key - 1, '0'));
    string remainder = mod2div(appended_data, key);
    string codeword = data + remainder;
    cout << "Remainder : " << remainder << "\n";
    cout << "Encoded Data (Data + Remainder) :" << codeword << "\n";
}
void receiver(string data, string key)
{
    string currxor = mod2div(data.substr(0, key.size()), key);
    int curr = key.size();
    while (curr != data.size())
    {
        if (currxor.size() != key.size())
        {
            currxor.push_back(data[curr++]);
        }
        else
        {
            currxor = mod2div(currxor, key);
        }
    }
    if (currxor.size() == key.size())
    {
        currxor = mod2div(currxor, key);
    }
    if (currxor.find('1') != string::npos)
    {
        cout << "there is some error in data" << endl;
    }
    else
    {
        cout << "correct message received" << endl;
    }
}
int main()
{
    string data;
    string generator;
    int frameSize, generatorSize;
    cout << "Enter the frame size: " << endl;
    cin >> frameSize;
    cout << "Enter the generator size: " << endl;
    cin >> generatorSize;
    cout << "Enter the data:";
    cin >> data;
    cout << "Enter the generator:";
    cin >> generator;
    cout << "\nSender side..." << endl;
    encodeData(data, generator);
    cout << "\nReceiver side..." << endl;
    receiver(
        data + mod2div(data + std::string(generator.size() - 1, '0'), generator),
        generator);
    return 0;
}