Numeric Comparer for Sorting array numerically

NumericComparer.cs

    public class NumericComparer : System.Collections.IComparer
    {
        public NumericComparer()
        { }

        public int Compare(object x, object y)
        {
            if ((x is string) && (y is string))
            {
                return StringLogicalComparer.Compare((string)x, (string)y);
            }
            return -1;
        }
    }
    public class StringLogicalComparer
    {
        public static int Compare(string s1, string s2)
        {
            //get rid of special cases
            if ((s1 == null) && (s2 == null)) return 0;
            else if (s1 == null) return -1;
            else if (s2 == null) return 1;

            if ((s1.Equals(string.Empty) && (s2.Equals(string.Empty)))) return 0;
            else if (s1.Equals(string.Empty)) return -1;
            else if (s2.Equals(string.Empty)) return -1;

            //WE style, special case
            bool sp1 = Char.IsLetterOrDigit(s1, 0);
            bool sp2 = Char.IsLetterOrDigit(s2, 0);
            if (sp1 && !sp2) return 1;
            if (!sp1 && sp2) return -1;

            int i1 = 0, i2 = 0; //current index
            int r = 0; // temp result
            while (true)
            {
                bool c1 = Char.IsDigit(s1, i1);
                bool c2 = Char.IsDigit(s2, i2);
                if (!c1 && !c2)
                {
                    bool letter1 = Char.IsLetter(s1, i1);
                    bool letter2 = Char.IsLetter(s2, i2);
                    if ((letter1 && letter2) || (!letter1 && !letter2))
                    {
                        if (letter1 && letter2)
                        {
                            r = Char.ToLower(s1[i1]).CompareTo(Char.ToLower(s2[i2]));
                        }
                        else
                        {
                            r = s1[i1].CompareTo(s2[i2]);
                        }
                        if (r != 0) return r;
                    }
                    else if (!letter1 && letter2) return -1;
                    else if (letter1 && !letter2) return 1;
                }
                else if (c1 && c2)
                {
                    r = CompareNum(s1, ref i1, s2, ref i2);
                    if (r != 0) return r;
                }
                else if (c1)
                {
                    return -1;
                }
                else if (c2)
                {
                    return 1;
                }
                i1++;
                i2++;
                if ((i1 >= s1.Length) && (i2 >= s2.Length))
                {
                    return 0;
                }
                else if (i1 >= s1.Length)
                {
                    return -1;
                }
                else if (i2 >= s2.Length)
                {
                    return -1;
                }
            }
        }

        private static int CompareNum(string s1, ref int i1, string s2, ref int i2)
        {
            int nzStart1 = i1, nzStart2 = i2; // nz = non zero
            int end1 = i1, end2 = i2;

            ScanNumEnd(s1, i1, ref end1, ref nzStart1);
            ScanNumEnd(s2, i2, ref end2, ref nzStart2);
            int start1 = i1; i1 = end1 - 1;
            int start2 = i2; i2 = end2 - 1;

            int nzLength1 = end1 - nzStart1;
            int nzLength2 = end2 - nzStart2;

            if (nzLength1 < nzLength2) return -1;
            else if (nzLength1 > nzLength2) return 1;

            for (int j1 = nzStart1, j2 = nzStart2; j1 <= i1; j1++, j2++)
            {
                int r = s1[j1].CompareTo(s2[j2]);
                if (r != 0) return r;
            }
            // the nz parts are equal
            int length1 = end1 - start1;
            int length2 = end2 - start2;
            if (length1 == length2) return 0;
            if (length1 > length2) return -1;
            return 1;
        }

        //lookahead
        private static void ScanNumEnd(string s, int start, ref int end, ref int nzStart)
        {
            nzStart = start;
            end = start;
            bool countZeros = true;
            while (Char.IsDigit(s, end))
            {
                if (countZeros && s[end].Equals('0'))
                {
                    nzStart++;
                }
                else countZeros = false;
                end++;
                if (end >= s.Length) break;
            }
        }
    }//EOC