HoldemHand.Hand.GapCount C# (CSharp) Method

        public static int GapCount(ulong mask)
        {
            int start, end;

            if (BitCount(mask) != 2) return -1;

            uint bf = CardMask(mask, Clubs) |
                        CardMask(mask, Diamonds) |
                        CardMask(mask, Hearts) |
                        CardMask(mask, Spades);

            if (BitCount(bf) != 2) return -1;

            for (start = 12; start >= 0; start--)
            {
                if ((bf & (1UL << start)) != 0)
                    break;
            }

            for (end = start - 1; end >= 0; end--)
            {
                if ((bf & (1UL << end)) != 0)
                    break;
            }

            // Handle wrap
            if (start == 12 && end == 0) return 0;
            if (start == 12 && end == 1) return 1;
            if (start == 12 && end == 2) return 2;
            if (start == 12 && end == 3) return 3;

            return (start-end-1 > 3 ? -1 : start-end-1);
        }