public static uint PeakPairToHash(PeakPair pp)
{
// Put frequency bins and the distance each in one byte. The actual quantization
// is configured through the parameters, e.g. the FFT window size determines the
// number of frequency bins, and the size of the target zone determines the max
// distance. Their max size can be anywhere in the range of a byte. if it should be
// higher, a quantization step must be introduced (which will basically be a division).
return((uint)((byte)pp.Peak1.Index << 16 | (byte)pp.Peak2.Index << 8 | (byte)pp.Distance));
}
private void ConvertPairsToSubFingerprints(List <PeakPair> peakPairs, List <SubFingerprint> subFingerprints)
{
// This sorting step is needed for the Zipper intersection algorithm in the fingerprint
// store to find matching hashes, which expects them sorted by frame index. Sorting works
// because the index is coded in the most significant bits of the hashes.
var hashes = peakPairs.ConvertAll(pp => new SubFingerprintHash(PeakPair.PeakPairToHash(pp)));
hashes.Sort();
subFingerprints.AddRange(hashes.ConvertAll(h => new SubFingerprint(peakPairs[0].Index, h, false)));
}