/// <summary>
/// The constructor for deserialization.
/// </summary>
public HyperLogLogCore(SerializationInfo info, StreamingContext context)
{
_b = info.GetByte("b");
_m = 1 << _b;
_alpha = HyperLogLogInternals.CalculateConstantAlphaCorrectionFactor(_b);
_registers = (byte[])info.GetValue("registers", typeof(byte[]));
}
/// <summary>
/// Adds object's hash to the structure.
/// Hash needs to be produced by a 'good' hash function.
/// In practice it does not have to be cryptographycally secure.
/// </summary>
public void AddHash(ulong hash)
{
uint registerIndex = HyperLogLogInternals.CalculateRegisterIndex(hash, _b);
byte proposedRegisterValue = HyperLogLogInternals.PositionOfLeftMostOne(hash, _b);
byte newValueOfRegister = Math.Max(proposedRegisterValue, _registers[registerIndex]);
_registers[registerIndex] = newValueOfRegister;
}
/// <summary>
/// Creates HyperLogLogCore instance.
/// </summary>
/// <param name="b">
/// Number of bits of hash used to calculate register index.
/// There will be 2^b registers.
/// The bigger the value of b the better accuraccy of count will be achieved.
/// On the other hand, the greater the value of b, more memory will be used for the registers.
/// </param>
public HyperLogLogCore(byte b)
{
if (b < 4 || b > 16)
{
throw new ArgumentOutOfRangeException(nameof(b), "Parameter 'b' must have value between 4 inclusive and 16 inclusive");
}
_b = b;
_m = 1 << _b;
_registers = new byte[_m];
_alpha = HyperLogLogInternals.CalculateConstantAlphaCorrectionFactor(_b);
}
/// <summary>
/// Returns estimated count of distict hashes added to HyperLogLogCore.
/// There is not caching, estimated count is calculated on every call of this method.
/// </summary>
public int CalculateEstimatedCount()
{
double z = 0;
for (int j = 0; j < _m; j++)
{
z += 1.0 / (1 << _registers[j]);
}
z = 1 / z;
double rawEstimate = _alpha * _m * _m * z;
return(HyperLogLogInternals.AdjustForSmallOrBigRanges(rawEstimate, _registers));
}
