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Serializable pseudo-random number generators and distributions.
/*
* Copyright (c) 2022-2023 See AUTHORS file.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package com.github.tommyettinger.random;
/**
* A relatively-simple RNG that's similar to {@link LaserRandom} with less correlation between similar initial states,
* but without the ability to {@link #skip(long)}. It has two {@code long} states, one of which changes with every
* generated value and one always-odd state which never changes (the "stream"). This uses a linear congruential
* generator for its changing state (the state changes by multiplying with a large constant and adding the stream), and
* feeds the resulting value to a small, simple unary hash to get a more-random result.
*
* This always has a period of 2 to the 64, and there are 2 to the 63 possible sequences that result from changing the
* stream value. MizuchiRandom implements all optional methods in EnhancedRandom except
* {@link #skip(long)}; it does implement {@link #previousLong()} without using skip().
*
* MizuchiRandom passes 64TB of testing with PractRand, which uses a suite of tests to look for a variety of potential
* problems. It has not been tested with hwd or remortality. All the generators here are considered stable.
*
* The name comes from combining the concept of a dragon, with streams. A mythological theme was carried throughout some
* generators that I designed and that were designed by others, such as Fortuna. Mizuchi allows many possible streams, so
* the mizuchi, a (by some versions of the story) river dragon from Japanese mythology, seemed fitting.
*
* This is present here for two reasons. First, it can be used in cases where similar initial states are expected to be
* given to a two-state generator like LaserRandom (visible patterns are obviously correlated with LaserRandom but are
* not at all correlated with MizuchiRandom). Second, MizuchiRandom is often the fastest 64-bit generator available in
* the closely-related C# library ShaiRandom, and for compatibility purposes it makes sense to support this in both.
* This generator is not especially fast here compared to LaserRandom, especially on OpenJ9, nor is it fast compared to
* FourWheelRandom on HotSpot JDKs, but it does maintain its quality well.
*/
public class MizuchiRandom extends EnhancedRandom {
/**
* The first state, also called the changing state; can be any long.
*/
protected long stateA;
/**
* The second state, also called the stream; can be any odd-number long.
*/
protected long stateB;
/**
* Creates a new MizuchiRandom with a random state.
*/
public MizuchiRandom () {
super();
stateA = EnhancedRandom.seedFromMath();
stateB = EnhancedRandom.seedFromMath() | 1L;
}
/**
* Creates a new MizuchiRandom with the given seed; all {@code long} values are permitted.
* The seed will be passed to {@link #setSeed(long)} to attempt to adequately distribute the seed randomly.
*
* @param seed any {@code long} value
*/
public MizuchiRandom (long seed) {
super(seed);
setSeed(seed);
}
/**
* Creates a new MizuchiRandom with the given two states; all {@code long} values are permitted for
* stateA, and all odd-number {@code long} values are permitted for stateB. These states are not
* changed as long as they are permitted values.
*
* @param stateA any {@code long} value
* @param stateB any {@code long} value; should be odd, otherwise this will add 1 to make it odd
*/
public MizuchiRandom (long stateA, long stateB) {
super(stateA);
this.stateA = stateA;
this.stateB = stateB | 1L;
}
@Override
public String getTag() {
return "MizR";
}
/**
* This generator has 2 {@code long} states, so this returns 2.
*
* @return 2 (two)
*/
@Override
public int getStateCount () {
return 2;
}
/**
* Gets the state determined by {@code selection}, as-is.
* Selections 0 (or any even number) and 1 (or any odd number) refer to states A and B.
*
* @param selection used to select which state variable to get; generally 0 or 1
* @return the value of the selected state
*/
@Override
public long getSelectedState (int selection) {
if ((selection & 1) == 1) {
return stateB;
}
return stateA;
}
/**
* Sets one of the states, determined by {@code selection}, to {@code value}, as-is.
* Selections 0 (or any even number) and 1 (or any odd number) refer to states A and B.
*
* @param selection used to select which state variable to set; generally 0 or 1
* @param value the exact value to use for the selected state, if valid
*/
@Override
public void setSelectedState (int selection, long value) {
if ((selection & 1) == 1) {
stateB = value | 1L;
} else {
stateA = value;
}
}
/**
* This initializes both states of the generator to random values based on the given seed.
* (2 to the 64) possible initial generator states can be produced here.
*
* @param seed the initial seed; may be any long
*/
@Override
public void setSeed (long seed) {
long x = (seed += 0x9E3779B97F4A7C15L);
x ^= x >>> 27;
x *= 0x3C79AC492BA7B653L;
x ^= x >>> 33;
x *= 0x1C69B3F74AC4AE35L;
stateA = x ^ x >>> 27;
x = (seed + 0x9E3779B97F4A7C15L);
x ^= x >>> 27;
x *= 0x3C79AC492BA7B653L;
x ^= x >>> 33;
x *= 0x1C69B3F74AC4AE35L;
stateB = (x ^ x >>> 27) | 1L;
}
public long getStateA () {
return stateA;
}
/**
* Sets the first part of the state (the changing state).
*
* @param stateA can be any long
*/
public void setStateA (long stateA) {
this.stateA = stateA;
}
public long getStateB () {
return stateB;
}
/**
* Sets the second part of the state (the stream). This must be odd, otherwise this will add 1 to make it odd.
*
* @param stateB can be any odd-number long; otherwise this adds 1 to make it odd
*/
public void setStateB (long stateB) {
this.stateB = stateB | 1L;
}
/**
* Sets the state completely to the given three state variables.
* This is the same as calling {@link #setStateA(long)} and {@link #setStateB(long)}
* as a group.
*
* @param stateA the first state; can be any long
* @param stateB the second state; can be any odd-number long
*/
@Override
public void setState (long stateA, long stateB) {
this.stateA = stateA;
this.stateB = stateB | 1L;
}
@Override
public long nextLong () {
long z = (stateA = stateA * 0xF7C2EBC08F67F2B5L + stateB);
z = (z ^ z >>> 23 ^ z >>> 47) * 0xAEF17502108EF2D9L;
return (z ^ z >>> 25);
}
@Override
public long previousLong () {
long z = stateA;
stateA = (stateA - stateB) * 0x09795DFF8024EB9DL;
z = (z ^ z >>> 23 ^ z >>> 47) * 0xAEF17502108EF2D9L;
return z ^ z >>> 25;
}
@Override
public int next (int bits) {
long z = (stateA = stateA * 0xF7C2EBC08F67F2B5L + stateB);
z = (z ^ z >>> 23 ^ z >>> 47) * 0xAEF17502108EF2D9L;
return (int)(z ^ z >>> 25) >>> (32 - bits);
}
@Override
public MizuchiRandom copy () {
return new MizuchiRandom(stateA, stateB);
}
@Override
public boolean equals (Object o) {
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
MizuchiRandom that = (MizuchiRandom)o;
if (stateA != that.stateA)
return false;
return stateB == that.stateB;
}
public String toString () {
return "MizuchiRandom{" + "stateA=" + (stateA) + "L, stateB=" + (stateB) + "L}";
}
}