/// <summary>
/// Calculate hamming distance of bits for two fingerprints (normal a fingerprint contains 256 subfingerprints)
/// The return value is the Bit Error Rate.
/// For 256 subfingerprints a BER lower than 2867 is considered a match
/// </summary>
public static int HammingDistance(uint[] fingerprint1, uint[] fingerprint2)
{
if (fingerprint1 == null || fingerprint2 == null)
{
throw new Exception("fingerprint1 or fingerprint2 is null");
}
else if (fingerprint1.Length != fingerprint2.Length)
{
throw new Exception(string.Format("fingerprint1 and fingerprint2 must be of equal length ({0} != {1})", fingerprint1.Length, fingerprint2.Length));
}
// length of both needs to be equal!
int BER = 0; // Bit Error Rate
for (int i = 0; i < fingerprint1.Length; i++)
{
int bits = SimilarityUtility.HammingDistance(fingerprint1[i], fingerprint2[i]);
if (bits > 0)
{
BER += bits;
}
} // for i
return(BER);
}
/// <summary>
/// Creates a lookup dictionary from the fingerprintsignature. Key is the hash an value is an array of int
/// pointing (index) to where the hash can be found using "SubFingerprint(int index)"
/// </summary>
public static Dictionary <uint, int[]> CreateLookupDictionary(FingerprintSignature fs, bool filterNoneRandomHashes = true)
{
Dictionary <uint, int[]> subFingerLookup = new Dictionary <uint, int[]>(fs.SubFingerprintCount);
for (int index = 0; index < fs.SubFingerprintCount; index++)
{
uint h = BitConverter.ToUInt32(fs.Signature, index * 4);
if (filterNoneRandomHashes)
{
int bits = SimilarityUtility.HammingDistance(h, 0);
if (bits < 10 || bits > 22) // 5 27 (10 22)
{
// try further in the fingerprint
continue;
}
}
int[] data = new int[1] {
index
};
if (subFingerLookup.ContainsKey(h))
{
subFingerLookup[h] = CombineArrays(subFingerLookup[h], data);
}
else
{
subFingerLookup.Add(h, data);
}
} //foreach
return(subFingerLookup);
}
public FingerprintSignature(object reference, long titelnummerTrackID, byte[] signature, long durationInMS, bool createLookupIndex = false)
{
SimilarityUtility.InitSimilarityUtility();
this.titelnummerTrackID = titelnummerTrackID;
this.reference = reference;
if (this.signature != null)
{
Signature = signature;
}
this.durationInMS = durationInMS;
if (createLookupIndex)
{
dSubFingerLookup = CreateLookupDictionary();
}
}
/// <summary>
/// Calculate the BER between 2 fingerprints
/// </summary>
public static int BER(FingerprintSignature f1, FingerprintSignature f2)
{
if (f1.SubFingerprintCount != f2.SubFingerprintCount)
{
return(-1);
}
// length of both needs to be equal!
int BER = 0; // Bit Error Rate
for (int i = 0; i < f1.SubFingerprintCount; i++)
{
int bits = SimilarityUtility.HammingDistance(f1.SubFingerprint(i), f2.SubFingerprint(i));
if (bits > 0)
{
BER += bits;
}
} // for i
return(BER);
}
