/// <summary>
/// Subtract the given Bloom filter, resulting in the difference.
/// </summary>
/// <param name="bloomFilterData"></param>
/// <remarks>Results in the symmetric difference of the two Bloom filters.</remarks>
public virtual void Subtract(IBloomFilterData bloomFilterData)
{
if (bloomFilterData == null)
{
return;
}
var foldedSize = _configuration.FoldingStrategy?.GetFoldFactors(_blockSize, bloomFilterData.BlockSize);
if (bloomFilterData.BlockSize != BlockSize &
foldedSize == null)
{
throw new ArgumentException("Bloom filters of different sizes cannot be subtracted.", nameof(bloomFilterData));
}
var otherBitArray = new FastBitArray(bloomFilterData.Bits ?? EmptyByteArray)
{
Length = (int)bloomFilterData.BlockSize
};
if (foldedSize != null &&
(foldedSize.Item2 != 1 ||
foldedSize.Item1 != 1))
{
if (foldedSize.Item1 != 1)
{
Fold((uint)foldedSize.Item1, true);
}
if (foldedSize.Item2 != 1)
{
for (var i = 0; i < _data.Length; i++)
{
_data.Set(i, _data.Get(i) ^ GetFolded(otherBitArray, i, (uint)foldedSize.Item2));
}
ItemCount = EstimateItemCount(_data, _hashFunctionCount);
return;
}
}
_data = _data.Xor(otherBitArray);
ItemCount = EstimateItemCount(_data, _hashFunctionCount);
}