natix.CompactDS.RRR.Rank1AccessBackend C# (CSharp) Method

        int Rank1AccessBackend(int pos, out bool last_bit)
        {
            // in advance, we use pos as a simple counter of the remaining positions
            int blockIndex = pos / 15 / this.BlockSize;
            int classIndex = blockIndex * this.BlockSize;
            int rank = this.AbsRank[blockIndex];
            pos -= classIndex * 15;
            int offset = this.AbsOffset[blockIndex];
            int klass;
            var ctx = new CtxCache (-1);
            if (pos >= 15) {
                for (; pos >= 15; pos -= 15) {
                    klass = this.DecodeClass (classIndex, ctx);
                    classIndex++;
                    rank += klass;
                    int numbits = NumBits[klass];
                    offset += numbits;
                }
            }
            klass = this.DecodeClass (classIndex, ctx);
            uint block = (uint)this.ReadBlock (klass, offset);
            last_bit = BitAccess.GetBit ((int)block, pos);
            rank += BitAccess.Rank1 (block, pos);
            return rank;
        }