Quickest way to convert a base 10 number to any base in .NET?

Question

I have and old(ish) C# method I wrote that takes a number and converts it to any base:

string ConvertToBase(int number, char[] baseChars);

Answer 1

I recently blogged about this. My implementation does not use any string operations during the calculations, which makes it very fast. Conversion to any numeral system with base from 2 to 36 is supported:

/// 

/// Converts the given decimal number to the numeral system with the
/// specified radix (in the range [2, 36]).
/// 
/// The number to convert.
/// The radix of the destination numeral system (in the range [2, 36]).
/// 
public static string DecimalToArbitrarySystem(long decimalNumber, int radix)
{
    const int BitsInLong = 64;
    const string Digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    if (radix < 2 || radix > Digits.Length)
        throw new ArgumentException("The radix must be >= 2 and <= " + Digits.Length.ToString());

    if (decimalNumber == 0)
        return "0";

    int index = BitsInLong - 1;
    long currentNumber = Math.Abs(decimalNumber);
    char[] charArray = new char[BitsInLong];

    while (currentNumber != 0)
    {
        int remainder = (int)(currentNumber % radix);
        charArray[index--] = Digits[remainder];
        currentNumber = currentNumber / radix;
    }

    string result = new String(charArray, index + 1, BitsInLong - index - 1);
    if (decimalNumber < 0)
    {
        result = "-" + result;
    }

    return result;
}

I've also implemented a fast inverse function in case anyone needs it too: Arbitrary to Decimal Numeral System.