C# Why can equal decimals produce unequal hash values?

Question

We ran into a magic decimal number that broke our hashtable. I boiled it down to the following minimal case:

decimal d0 = 295.50000000000000000000000000m;
de         


        

Answer 1

Another bug (?) that results in different bytes representation for the same decimal on different compilers: Try to compile following code on VS 2005 and then VS 2010. Or look at my article on Code Project.

class Program
{
    static void Main(string[] args)
    {
        decimal one = 1m;

        PrintBytes(one);
        PrintBytes(one + 0.0m); // compare this on different compilers!
        PrintBytes(1m + 0.0m);

        Console.ReadKey();
    }

    public static void PrintBytes(decimal d)
    {
        MemoryStream memoryStream = new MemoryStream();
        BinaryWriter binaryWriter = new BinaryWriter(memoryStream);

        binaryWriter.Write(d);

        byte[] decimalBytes = memoryStream.ToArray();

        Console.WriteLine(BitConverter.ToString(decimalBytes) + " (" + d + ")");
    }
}

Some people use following normalization code d=d+0.0000m which is not working properly on VS 2010. Your normalization code (d=d/1.000000000000000000000000000000000m) looks good - I use the same one to get the same byte array for the same decimals.