natix.CompactDS.RRR.Select1 C# (CSharp) Method

        public override int Select1(int rank)
        {
            if (rank < 1) {
                return -1;
            }
            int blockIndex = GenericSearch.FindFirst<int> (rank, this.AbsRank);
            if (this.AbsRank[blockIndex] == rank) {
                blockIndex--;
            }
            int classIndex = blockIndex * this.BlockSize;
            rank -= this.AbsRank[blockIndex];
            int pos = classIndex * 15;
            int offset = this.AbsOffset[blockIndex];
            int klass;
            var ctx = new CtxCache (-1);
            while (rank > 0) {
                klass = this.DecodeClass (classIndex, ctx);
                if (rank - klass <= 0) {
                    break;
                }
                classIndex++;
                pos += 15;
                rank -= klass;
                int numbits = NumBits[klass];
                offset += numbits;
            }
            if (rank > 0) {
                klass = this.DecodeClass (classIndex, ctx);
                uint block = (uint)this.ReadBlock (klass, offset);
                // Console.WriteLine ("rank: {0}, pos: {1}, block: {2}, klass: {3}, offset: {4}",
                //	rank, pos, block, klass, offset);
                pos += BitAccess.Select1 (block, rank);
            }
            return pos;
        }