Numeric comparer

public class NumericComparer : IComparer<string>
{
    #region IComparer implementation
    public int Compare (string x, string y)
    {
        if (x == y)
            return 0;

        int xi = 0;
        int yi = 0;

        while (xi < x.Length && yi < y.Length) {
            while(xi < x.Length && char.IsWhiteSpace(x[xi])) xi++;
            while(yi < y.Length && char.IsWhiteSpace(y[yi])) yi++;

            if(char.IsDigit(x[xi]) && char.IsDigit(y[yi]))
            {
                string xDigits = "";

                do
                {
                    xDigits += x[xi];
                    xi++;
                }
                while(xi < x.Length && char.IsDigit(x[xi]));

                string yDigits = "";

                do
                {
                    yDigits += y[yi];
                    yi++;
                }
                while(yi < y.Length && char.IsDigit(y[yi]));

                int xVal = ParseDigits(xDigits);
                int yVal = ParseDigits(yDigits);

                if(xVal > yVal) return 1;
                else if (xVal < yVal) return -1;
            }
            else if(x[xi] != y[yi])
            {
                return x[xi].CompareTo(y[yi]);
            }
            else
            {
                xi++;
                yi++;
            }
        }

        return 0;
    }

    public static int ParseDigits (string digits)
    {
        string newDigits = "";

        foreach (char c in digits) {
            if (c >= '0' && c <= '9')
                newDigits += c;
            else if (c >= '\uFF10' && c <= '\uFF19')
                newDigits += (char)(c - '\uFF10' + '0');
            else if (c >= '\u0660' && c <= '\u0669')
                newDigits += (char)(c - '\u0660' + '0');
            else if (c >= '\u09E6' && c <= '\u09EF')
                newDigits += (char)(c - '\u09E6' + '0');
        }

        if (newDigits == "")
            return 0;
        else
            return int.Parse (newDigits);
    }
    #endregion
}