public void DecodingTest()
{
HashEncodingHelper encodingHelper = new HashEncodingHelper(14, 25);
int encodedHash;
int expectedIndex;
byte expectedR;
encodedHash = 638739; // 1001 1011 1111 0001 0011
expectedIndex = 4990; // 1 0011 0111 1110
expectedR = 20; // 1001 + ToBinary(25 - 14)
DecodeAndAssert(encodingHelper, encodedHash, expectedIndex, expectedR);
encodedHash = 3567856; // 11 0110 0111 0000 1111 0000
expectedIndex = 14456; // 11 1000 0111 1000
expectedR = 3; // 11
DecodeAndAssert(encodingHelper, encodedHash, expectedIndex, expectedR);
encodedHash = 10; // 1010
expectedIndex = 5; // 111
expectedR = 7; // 101
DecodeAndAssert(encodingHelper, encodedHash, expectedIndex, expectedR);
encodedHash = 265822207; // 1111 1101 1000 0001 1111 1111 1111
expectedIndex = 12351; // 11 0000 0011 1111
expectedR = 74; // 11 1111 + ToBinary(25 - 14)
DecodeAndAssert(encodingHelper, encodedHash, expectedIndex, expectedR);
}
private void DecodeAndAssert(HashEncodingHelper encodingHelper, int encodedHash, int expectedIndex, byte expectedR)
{
int idx;
byte r;
encodingHelper.DecodeHash(encodedHash, out idx, out r);
Assert.AreEqual(expectedR, r, "decoded value should be as expected"); // 11
Assert.AreEqual(expectedIndex, idx, "decoded index should be as expected"); // 11 1000 0111 1000
}
/// <summary>
/// Creates a hyperloglog++ instance.
/// </summary>
/// <param name="precision">The higher the precision, the higher the accuracy, but also the memory usage. Must be in [4, max(28, sparsePrecision)].</param>
/// <param name="sparsePrecision">The precision of the sparse representation. Must be inferior or equal to 63.</param>
public HyperLogLogPlusPlus(byte precision, byte sparsePrecision)
: base(precision)
{
int precisionLimit = Math.Min(sparsePrecision, (byte)28);
if (precision < MIN_PRECISION || precision > precisionLimit)
throw new ArgumentException(string.Format("The precision {0} must be between 4 and {1}", precision, precisionLimit));
if (sparsePrecision > MAX_SPARSE_PRECISION)
throw new ArgumentException(string.Format("The sparse precision {0} must be inferior or equal to 63.", sparsePrecision));
SparseRepresentationThreshold = Convert.ToInt32(6 * M);
SparsePrecision = sparsePrecision;
HashEncoder = new HashEncodingHelper(precision, sparsePrecision);
}
private void EncodeWithPrecisionsAndAssert(ulong hash, uint expectedEncodedHash, byte precision, byte sparsePrecision)
{
int encodedHash = new HashEncodingHelper(precision, sparsePrecision).EncodeHash(hash);
Assert.AreEqual(expectedEncodedHash, (uint)encodedHash, "encoded hashes should be the same");
}
