This an implementation of a BigInteger and includes full C# source in a single file. The implementation supports BigIntegers of arbitrary size and is compatible with C# 2.0 (and might also work with earlier compiler releases). Objects support all of the usual arithmetic and relational operators.
I originally wrote this for C# 1.1 and I could (and should) now drop the lame internal representation of the "byte" array and replace it with a generic argument to the internal class that manages the byte array. I wrote things this way because I had different scenarios where the average size of the integer was vastly different and I wanted to be sure I could change the internal representation based on my final performance requirements.
For a description of the algorithms, see D. Knuth, The Art of Computer Programming, Volume 2.
public class MainProgram
public static void Main(string args)
BigInteger a = new BigInteger(25);
a = a + 100;
BigInteger b = new BigInteger("139435810094598308945890230913");
BigInteger c = b / a;
BigInteger d = b % a;
BigInteger e = (c * a) + d;
if (e != b)
Console.WriteLine("Can never be true.");
I would just cut and paste the source code from BigInteger.cs into your own project and change the name space ScottGarland.BigInteger to whatever you want. The DType will replaced with a generic parameter to the DigitsArray class in the next release. If you want to change the internal arithmetic base type - by default it's System.UInt32 - look at the first part of the source in BigInteger.cs and you'll see a using statement with some commented alternatives.