Question

System.Numerics.BigInteger lets you multiply large integers together, but is there anything of the same type for floating point numbers? If not, is there a free library I can use?

//this but with floats
System.Numerics.BigInteger maxint = new BigInteger(int.MaxValue);

System.Numerics.BigInteger big = maxint * maxint * maxint;
System.Console.WriteLine(big);

Answer 1

Perhaps you’re looking for BigRational? Microsoft released it under their BCL project on CodePlex. Not actually sure how or if it will fit your needs.

It keeps it as a rational number. You can get the a string with the decimal value either by casting or some multiplication.

var r = new BigRational(5000, 3768);
Console.WriteLine((decimal)r);
Console.WriteLine((double)r);

Or with a simple(ish) extension method like this:

public static class BigRationalExtensions
{
    public static string ToDecimalString(this BigRational r, int precision)
    {
        var fraction = r.GetFractionPart();

        // Case where the rational number is a whole number
        if(fraction.Numerator == 0 && fraction.Denominator == 1)
        {
            return r.GetWholePart() + ".0";
        }

        var adjustedNumerator = (fraction.Numerator
                                           * BigInteger.Pow(10, precision));
        var decimalPlaces = adjustedNumerator / fraction.Denominator;

        // Case where precision wasn't large enough.
        if(decimalPlaces == 0)
        {
            return "0.0";
        }

        // Give it the capacity for around what we should need for 
        // the whole part and total precision
        // (this is kinda sloppy, but does the trick)
        var sb = new StringBuilder(precision + r.ToString().Length);

        bool noMoreTrailingZeros = false;
        for (int i = precision; i > 0; i--)
        {
            if(!noMoreTrailingZeros)
            {
                if ((decimalPlaces%10) == 0)
                {
                    decimalPlaces = decimalPlaces/10;
                    continue;
                }

                noMoreTrailingZeros = true;
            }

            // Add the right most decimal to the string
            sb.Insert(0, decimalPlaces%10);
            decimalPlaces = decimalPlaces/10;
        }

        // Insert the whole part and decimal
        sb.Insert(0, ".");
        sb.Insert(0, r.GetWholePart());

        return sb.ToString();
    }
}

If it’s out of the precision range of a decimal or double, they will be cast to their respective types with a value of 0.0. Also, casting to decimal, when the result is outside of its range, will cause an OverflowException to be thrown.

The extension method I wrote (which may not be the best way to calculate a fraction’s decimal representation) will accurately convert it to a string, with unlimited precision. However, if the number is smaller than the precision requested, it will return 0.0, just like decimal or double would.