futuresecurity

/* How to deterministically initalize a PRNG from (x, y) coordinates. The
 * exact algorithm choice is arbitrary. `coordToLong` could be even simpler.
 * The "hash" is a good scrambling function from 64-bit input to 64-bit
 * output. Hashing might be redundant for certain PRNG implementations, but
 * only if the implementation already mixes seeds very well. (Similar seeds
 * can produce outputs with the same patterns.) If you use another RNG then
 * you need to bundle its source with your project. C's "srand" should not
 * be used because the same seed can produce different results on different 
 * platforms.
 */

futuresecurity

default int nextInt_Biased(int upperBound)
{
  if (upperBound == 0) { return nextInt(); }
  if (upperBound == 1) { return 0; }

  final long unsignedLimit = upperBound & 0xFFFF_FFFFL;
  final int log2Ceil = 64 - Long.numberOfLeadingZeros(unsignedLimit - 1);
  final int bitsOfRandomness = 64 - log2Ceil;
  final long rand = nextUnsignedLongBits(bitsOfRandomness);
  return (int)(long)((rand * unsignedLimit) >>> bitsOfRandomness);

futuresecurity

package io.github.futuresecurity.random.sampling;

import io.github.futuresecurity.random.UniformGenerator;

import java.util.SplittableRandom;

public class BoundedIntSampling
{
  public static int randomInt_TwoFactor32(int bound, UniformGenerator rng)
  {