Problem with calculating CRC

Damian7546

When I test my data to calculate CRC in below online calculator:
0x31 0x1c 0x4c 0x50 0x43
https://crccalc.com/?crc=0x31 0x1c 0x4c 0x50 0x43&method=CRC-16&datatype=hex&outtype=hex

I get CRC-16/ARC = 0x72C6 . And it is a properly value.

When I try calculate this sum in Qt like below I have different output ?

QByteArray testData;
testData.append(0x31); 
testData.append(0x1C);  
testData.append(0x4C);  
testData.append(0x50);  
testData.append(0x43);  
quint16 crc = calculateCrc(testData);

quint16 calculateCrc(const QByteArray &data)
{
    quint16 crc = 0x0000;  // Init = 0 (ARC standard)
    for (char byte : data) {
        crc ^= (static_cast<quint8>(byte) << 8);  // XOR high byte
        for (int i = 0; i < 8; i++) {
            crc = (crc & 0x8000) ? (crc << 1) ^ 0x8005 : (crc << 1);
        }
    }
    return crc;

}

What is wrong ?

SGaist

Hi,
I think you went the too complicated road:

quint16 calculateCrc16Arc(const QByteArray &data)
{
    quint16 crc = 0x0000;
    const quint16 poly = 0xA001;

    for (char byte : data) {
        crc ^= (static_cast<quint8>(byte));
        for (int i = 0; i < 8; i++) {
            crc = (crc & 0x0001) > 0 ? (crc >> 1) ^ poly : (crc >> 1);
        }
    }
    return crc;
}

Christian Ehrlicher

You get 5C82 with the code above which looks like CRC16/UMTS according to the page you linked. So you are using the wrong algorithm, not related to Qt.

Damian7546

@Christian-Ehrlicher ,So what algorithm I should use ?

SGaist

Hi,
I think you went the too complicated road:

quint16 calculateCrc16Arc(const QByteArray &data)
{
    quint16 crc = 0x0000;
    const quint16 poly = 0xA001;

    for (char byte : data) {
        crc ^= (static_cast<quint8>(byte));
        for (int i = 0; i < 8; i++) {
            crc = (crc & 0x0001) > 0 ? (crc >> 1) ^ poly : (crc >> 1);
        }
    }
    return crc;
}