checksum.cpp

#include <iostream>
#include <vector>
using namespace std;

struct HexCharStruct        // Fixes char to hex stuff?
{
  unsigned char c;
  HexCharStruct(unsigned char _c) : c(_c) { }
};

inline ostream& operator<<(ostream& o, const HexCharStruct& hs)
{
  return (o << hex << (int)hs.c);
}

inline HexCharStruct hex(unsigned char _c)
{
  return HexCharStruct(_c);
}

unsigned char calChecksum(const vector<unsigned char> msg)
{
  unsigned char sum = 0;

  for (int i=1; i < msg.size(); i++)
  {
    sum += msg[i];
  }
  
  unsigned char check = 0x100 - (sum & 0xFF);

  return check;
}


// int main() // Use vector so that it can be trivialy long.
// {
//     unsigned char preamb = 0xFA;
//     unsigned char BID = 0xFF;
//     unsigned char MID = 0x30;
//     unsigned char LEN = 0x00;

//     //unsigned char check1 = 0x100 - ((BID + MID + LEN) & 0xFF); // This outputs the correct checksum.

//     vector<unsigned char> mess;

//     mess.push_back(preamb);
//     mess.push_back(BID);
//     mess.push_back(MID);
//     mess.push_back(LEN);
//     // Data chars would go here

//     unsigned char check = calChecksum(mess);

//     //cout << "Checksum is: " << hex(check) << endl;
//     mess.push_back(check);

//     cout << "GoToConfig message: ";

//     for (unsigned char c: mess) // Could instead be adding these to the buffer
//         cout << hex(c) << " "; 

//     cout << endl;

//     return 0;
// }