binary search

binary search

            int index = 0;
            int last = this.array.Length - 1;
            while (index <= last)
            {
                int mid = index + (last - index) / 2;

                IPAddressInfo info = this.array[mid];
                if (ip >= info.Start && ip <= info.End)
                {
                    return info.AreaCode;
                }
                else if (ip > info.Start)
                {
                    index = mid + 1;
                }
                else
                {
                    last = mid - 1;
                }
            }