[SOLVED] Fast pseudo random number generator for procedural content

Fast pseudo random number generator for procedural content

I am looking for a pseudo random number generator which would be specialized to work fast when it is given a seed before generating each number. Most generators I have seen so far assume you set seed once and then generate a long sequence of numbers. The only thing which looks somewhat similar to I have seen so far is Perlin Noise, but it generates too "smooth" data - for similar inputs it tends to produce similar results.

The declaration of the generator should look something like:

int RandomNumber1(int seed);

Or:

int RandomNumber3(int seedX, int seedY, int seedZ);

I think having good RandomNumber1 should be enough, as it is possible to implement RandomNumber3 by hashing its inputs and passing the result into the RandomNumber1, but I wrote the 2nd prototype in case some implementation could use the independent inputs.

The intended use for this generator is to use it for procedural content generator, like generating a forest by placing trees in a grid and determining a random tree species and random spatial offsets for each location.

The generator needs to be very efficient (below 500 CPU cycles), because the procedural content is created in huge quantities in real time during rendering.

Solution

Seems like you're asking for a hash-function rather than a PRNG. Googling 'fast hash function' yields several promising-looking results.

For example:

uint32_t hash( uint32_t a)
    a = (a ^ 61) ^ (a >> 16);
    a = a + (a << 3);
    a = a ^ (a >> 4);
    a = a * 0x27d4eb2d;
    a = a ^ (a >> 15);
    return a;
}

Edit: Yep, some hash functions definitely look more suitable than others.

For your purposes, it should be sufficient to eyeball thefunction and check that a single-bit change in the input will propagate to lots of output bits.