BitsetsNET.RoaringBitset.AndNot C# (CSharp) Method

        public IBitset AndNot(RoaringBitset otherSet)
        {
            RoaringBitset answer = new RoaringBitset();
            int pos1 = 0, pos2 = 0;
            int length1 = containers.Size, length2 = otherSet.containers.Size;

            while (pos1 < length1 && pos2 < length2)
            {
                ushort s1 = containers.GetKeyAtIndex(pos1);
                ushort s2 = otherSet.containers.GetKeyAtIndex(pos2);
                if (s1 == s2)
                {
                    Container c1 = containers.GetContainerAtIndex(pos1);
                    Container c2 = otherSet.containers.GetContainerAtIndex(pos2);
                    Container c = c1.AndNot(c2);
                    if (c.GetCardinality() > 0)
                    {
                        answer.containers.Append(s1, c);
                    }
                    ++pos1;
                    ++pos2;
                }
                else if (Utility.CompareUnsigned(s1, s2) < 0)
                { // s1 < s2
                    int nextPos1 = containers.AdvanceUntil(s2, pos1);
                    answer.containers.AppendCopy(containers, pos1, nextPos1);
                    pos1 = nextPos1;
                }
                else
                { // s1 > s2
                    pos2 = otherSet.containers.AdvanceUntil(s1, pos2);
                }
            }
            if (pos2 == length2)
            {
                answer.containers.AppendCopy(containers, pos1, length1);
            }
            return answer;
        }