Is the Random Generator from Delphi the same calculation as C# if fed the same seed?

Question

I'm translating some Delphi code into c# code when I ran into this. I don't have an environment setup for Delphi so I can't test it myself.

Delphi:

RandSeed := var1;
Result := Random($FF);

c#:

Random RandSeed = new Random(var1);
Result = RandSeed.Next(255);

Would these put the same value in Result? If not, any ideas on a way to do so?

Answer 1

The Delphi PRNG is a deterministic linear congruential generator with 134775813 as a and 1 as c, and returning the high 32 bits for range-limited numbers. Here's an implementation in C# that returns the same values as Delphi:

using System;

class DelphiRandom
{
    int _seed;

    public DelphiRandom(int seed)
    {
        _seed = seed;
    }

    int GetNext() // note: returns negative numbers too
    {
        _seed = _seed * 0x08088405 + 1;
        return _seed;
    }

    public int Next(int maxValue)
    {
        ulong result = (ulong) (uint) GetNext() * (ulong) (uint) maxValue;
        return (int) (result >> 32);
    }
}

class App
{
    static void Main()
    {
        DelphiRandom r = new DelphiRandom(42);
        for (int i = 0; i < 10; ++i)
            Console.WriteLine(r.Next(100));
    }
}

Answer 2

Certainly not, because they use different RNGs. You could perhaps use a RNG from the Windows API, create your own RNG or use some RNG library to achieve this.

Another way to make sure your RNG creates the same numbers for a given seed would be to write a DLL and use it for both Delphi and C#.

By the way, if you want to code a RNG yourself, Wikipedia is a good starting point to get the names of some usual generators. After you're done, you should run it through some statistical test to make sure it's "random" enough for you.