QByteArray checksum calc issue

bigguiness

Hello,

I had a network app that transmits data using a QByteArray. Part of my protocol has a "checksum" which is simply a quint16 sum of the bytes in the QByteArray. The checksum is then added to the end of the QByteArray before the data is transmitted:

QByteArray ba;
// initialize the byte array

// calc the checksum
quint16 checksum = 0;
for (int i = 0; i < ba.size(); i++)
    checksum += ba[i];

// add the checksum to the byte array
ba.append((checksum >> 0) & 0xff);
ba.append((checksum >> 8) & 0xff);

The issue I am seeing is that the checksum is not getting calculated properly. For example:

ba[0] = 0x11;    // expected checksum = 0x0011  calculated = 0x0011
ba[1] = 0x0b     // expected checksum = 0x001c  calculated = 0x001c
ba[2] = 0x01;    // expected checksum = 0x001d  calculated = 0x001d
ba[3] = 0x27;    // expected checksum = 0x0044  calculated = 0x0044
ba[4] = 0xfa;    // expected checksum = 0x013e  calculated = 0x003e !!!

Any ideas why the calculated checksum is dropping the upper byte?

Note, it does seem that as long as the byte array data is < 0x80 it does get added correctly. It only messes up if the data is >= 0x80.

Thanks

Christian Ehrlicher

@bigguiness said in QByteArray checksum calc issue:

checksum += ba[i];

QByteArray is a 'signed' char - convert it properly.