Question

Is there a standard, cross platform number generator/algorithm/library that if seeded with the same input (in my case a hash of some sort), always produces the same set of pseudo-random numbers?

Ideally, I’d like to be able to do this cross platform, in both Java and .Net on any target machine, and get the same consistent output (vaguely random integers).

If it’s not possible, I’ll roll my own (my randomness requirements are very low, basically being used to assign different colors to something based on it’s ID – I just want to always assign the same color to the same item, no matter what system I’m running on).

Answer 1

There is a very simple and well known RNG algorithm, “Multiply-with-Carry”, that could be easily implemented on all platforms that I know of. It has the properties that you are requesting; it is up to you to decide whether it’s randomness would be adequate.

From Wikipedia:

An example of a simple pseudo-random number generator is the Multiply-with-carry method invented by George Marsaglia. It is computationally fast and has good (albeit not cryptographically strong) randomness properties.

And here is the dead-simple implementation in C#, which you will have no trouble adapting to other languages:

static int m_w = 1337;      // Choose initialization value, must not be zero
static int m_z = 123123;    // Choose initialization value, must not be zero

int GetRandom() 
{
    m_z = 36969 * (m_z & 65535) + (m_z >> 16);
    m_w = 18000 * (m_w & 65535) + (m_w >> 16);
    return (m_z << 16) + m_w;  /* 32-bit result */
}

The initial values of m_w and m_z is the seed.