qChecksum generates unduplicatible checksum value

In the three sentences that describe qChecksum() the algorithm that this function implements is variously described as "CRC-16" and "CRC-16-CCITT". However, the output from it fails to conform to the output of geenrators for CRC-16, or any of the three CRC-16-CCITT algorithms for which I have generators (0x0000, 0xFFFF, 0x1D0F).

Attached is a file for which I want to generate a CRC-16 checksum. It is a binary file, read into a QByteArray from a QFile in its entirety. The size of the QByteArray is 0x20000, which exactly matches he size of the file on disk, which indicates that the QByteArray is not including a terminating '\0' character. The code snippet is:

quint16 GetCRC(const QByteArray & filestream)
{
    return qChecksum(filestream, filestream.size())
}

The qChecksum call returns 0x2BBD. My generators (which have been verified by two different programs, all of which return the same result) show:

• CRC-16: 0xDDBD (this is the desired result)
• CRC-16-CCITT(0x0000): 0x07BF
• CRC-16-CCITT(0xFFFF): 0x837F
• CRC-16-CCITT(0x1D0F): 0x09AF