natix.CompactDS.SeqXLB.Rank C# (CSharp) Method

        public int Rank(int symbol, int _pos)
        {
            if (_pos < 0) {
                return 0;
            }
            if (symbol == 0) {
                return (int)this.xl_bitmap.Rank1 (_pos);
            }
            long pos = symbol * ((long)this.Count);
            var rank_a = this.xl_bitmap.Rank1 (pos + _pos);
            var rank_b = this.xl_bitmap.Rank1 (pos - 1);
            return (int)(rank_a - rank_b);
        }