Question

What is a fastest way to convert int to 4 bytes in C# ?

Fastest as in execution time not development time.

My own solution is this code:

byte[] bytes = new byte[4];
unchecked
{
 bytes[0] = (byte)(data >> 24);
 bytes[1] = (byte)(data >> 16);
 bytes[2] = (byte)(data >> 8);
 bytes[3] = (byte)(data);
}

Right now I see that my solution outperforms both struct and BitConverter by couple of ticks.

I think the unsafe is probably the fastest option and accept that as an answer but I would prefer to use a managed option.

Answer 1

A byte* cast using unsafe code is by far the fastest:

    unsafe static void Main(string[] args) {
        int i = 0x12345678;
        byte* pi = (byte*)&i;
        byte lsb = pi[0];  
        // etc..
    }

That’s what BitConverter does as well, this code avoids the cost of creating the array.