All Your Base Are Belong To Us

I wanted to encode a number in Base 36. A simple enough task, but as these things sometimes do, this took me down the rabbit hole of wanting to create a generic routine. I needed a set of methods, one that would take an integer and convert it to an arbitrary base and another to convert it back to a Base 10 number. There are a bunch of examples floating around the web but I wanted to create my own (combining some of the best elements from the code I found). It's a relatively easy problem to solve but along the way I found some interesting tricks to speed up the process.

So here is my C# take on this old problem:

// Chars to use in Base conversion private const string BASE_DIGITS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";   /// <summary> /// Convert a base 10 number to a different base. /// </summary> /// <param name="number">Number to convert</param> /// <param name="radix">Base to convert the number into (2-62)</param> /// <returns>String</returns> public static string NumberToBase(long number, int radix) {     if (number == 0) return "0";   if (radix < 2 || radix > BASE_DIGITS.Length)     throw new ArgumentOutOfRangeException("radix", radix, "The Radix/Base must be between 2 and " + BASE_DIGITS.Length);     var baseChars = BASE_DIGITS.ToCharArray();   var charStack = new Stack<char>();   var num = Math.Abs(number);     while (num != 0) {     charStack.Push(baseChars[num % radix]);     num /= radix;   }   var result = new string(charStack.ToArray());   return number < 0 ? "-" + result : result; }   /// <summary> /// Convert a string in a different base to a base 10 number /// </summary> /// <param name="number">Number to convert</param> /// <param name="radix">Base to convert from</param> /// <returns>Int64</returns> public static long NumberFromBase(string number, int radix) {   if (radix < 2 || radix > BASE_DIGITS.Length)     throw new ArgumentOutOfRangeException("radix", radix, "The Radix/Base must be between 2 and " + BASE_DIGITS.Length);     long result = 0;   long multiplier = 1;     for(var i = number.Length - 1; i >= 0; i--) {     var c = number[i];     // This is the negative sign symbol     if (i == 0 && c == '-') {       result = -result;       break;     }       result += BASE_DIGITS.IndexOf(c) * multiplier;     multiplier *= radix;   }   return result; }

I used LINQPad to create a quick program to test it out.

void Main() {   Random r = new Random();   for (int i = -1000; i < 1000000; i++) {     var basex = r.Next(2, 62);     var encoded = NumberToBase(i, basex);     var decoded = NumberFromBase(encoded, basex);           if (i != decoded) {       Console.WriteLine("i: {0} enc: {1} dec: {2}", i, encoded, decoded);     }   } }