ISAACRandom.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.commons.rng.core.source32;
import java.util.Arrays;
import org.apache.commons.rng.core.util.NumberFactory;
/**
* A fast cryptographic pseudo-random number generator.
* <p>
* ISAAC (Indirection, Shift, Accumulate, Add, and Count) generates 32-bit
* random numbers.
* ISAAC has been designed to be cryptographically secure and is inspired
* by RC4.
* Cycles are guaranteed to be at least 2<sup>40</sup> values long, and they
* are 2<sup>8295</sup> values long on average.
* The results are uniformly distributed, unbiased, and unpredictable unless
* you know the seed.
* <p>
* This code is based (with minor changes and improvements) on the original
* implementation of the algorithm by Bob Jenkins.
*
* @see <a href="http://burtleburtle.net/bob/rand/isaacafa.html">
* ISAAC: a fast cryptographic pseudo-random number generator</a>
*
* @see <a href="https://en.wikipedia.org/wiki/ISAAC_(cipher)">ISAAC (Wikipedia)</a>
* @since 1.0
*/
public class ISAACRandom extends IntProvider {
/** Log of size of rsl[] and mem[]. */
private static final int SIZE_L = 8;
/** Size of rsl[] and mem[]. */
private static final int SIZE = 1 << SIZE_L;
/** Half-size of rsl[] and mem[]. */
private static final int H_SIZE = SIZE >> 1;
/** For pseudo-random lookup. */
private static final int MASK = SIZE - 1 << 2;
/** The golden ratio. */
private static final int GLD_RATIO = 0x9e3779b9;
/** The results given to the user. */
private final int[] rsl = new int[SIZE];
/** The internal state. */
private final int[] mem = new int[SIZE];
/** Count through the results in rsl[]. */
private int count;
/** Accumulator. */
private int isaacA;
/** The last result. */
private int isaacB;
/** Counter, guarantees cycle is at least 2^40. */
private int isaacC;
/** Service variable. */
private final int[] arr = new int[8];
/** Service variable. */
private int isaacX;
/** Service variable. */
private int isaacI;
/** Service variable. */
private int isaacJ;
/**
* Creates a new ISAAC random number generator.
*
* @param seed Initial seed
*/
public ISAACRandom(int[] seed) {
setSeedInternal(seed);
}
/** {@inheritDoc} */
@Override
protected byte[] getStateInternal() {
final int[] sRsl = Arrays.copyOf(rsl, SIZE);
final int[] sMem = Arrays.copyOf(mem, SIZE);
final int[] sRem = Arrays.copyOf(new int[] {count, isaacA, isaacB, isaacC}, 4);
final int[] s = new int[2 * SIZE + sRem.length];
System.arraycopy(sRsl, 0, s, 0, SIZE);
System.arraycopy(sMem, 0, s, SIZE, SIZE);
System.arraycopy(sRem, 0, s, 2 * SIZE, sRem.length);
return composeStateInternal(NumberFactory.makeByteArray(s),
super.getStateInternal());
}
/** {@inheritDoc} */
@Override
protected void setStateInternal(byte[] s) {
final byte[][] c = splitStateInternal(s, (2 * SIZE + 4) * 4);
final int[] tmp = NumberFactory.makeIntArray(c[0]);
System.arraycopy(tmp, 0, rsl, 0, SIZE);
System.arraycopy(tmp, SIZE, mem, 0, SIZE);
final int offset = 2 * SIZE;
count = tmp[offset];
isaacA = tmp[offset + 1];
isaacB = tmp[offset + 2];
isaacC = tmp[offset + 3];
super.setStateInternal(c[1]);
}
/**
* Reseeds the RNG.
*
* @param seed Seed. Cannot be null.
*/
private void setSeedInternal(int[] seed) {
final int seedLen = seed.length;
final int rslLen = rsl.length;
System.arraycopy(seed, 0, rsl, 0, Math.min(seedLen, rslLen));
if (seedLen < rslLen) {
for (int j = seedLen; j < rslLen; j++) {
final long k = rsl[j - seedLen];
rsl[j] = (int) (0x6c078965L * (k ^ k >> 30) + j & 0xffffffffL);
}
}
initState();
}
/** {@inheritDoc} */
@Override
public int next() {
if (count < 0) {
isaac();
count = SIZE - 1;
}
return rsl[count--];
}
/** Generate 256 results. */
private void isaac() {
isaacI = 0;
isaacJ = H_SIZE;
isaacB += ++isaacC;
while (isaacI < H_SIZE) {
isaac2();
}
isaacJ = 0;
while (isaacJ < H_SIZE) {
isaac2();
}
}
/** Intermediate internal loop. */
private void isaac2() {
isaacX = mem[isaacI];
isaacA ^= isaacA << 13;
isaacA += mem[isaacJ++];
isaac3();
isaacX = mem[isaacI];
isaacA ^= isaacA >>> 6;
isaacA += mem[isaacJ++];
isaac3();
isaacX = mem[isaacI];
isaacA ^= isaacA << 2;
isaacA += mem[isaacJ++];
isaac3();
isaacX = mem[isaacI];
isaacA ^= isaacA >>> 16;
isaacA += mem[isaacJ++];
isaac3();
}
/** Lowest level internal loop. */
private void isaac3() {
mem[isaacI] = mem[(isaacX & MASK) >> 2] + isaacA + isaacB;
isaacB = mem[(mem[isaacI] >> SIZE_L & MASK) >> 2] + isaacX;
rsl[isaacI++] = isaacB;
}
/** Initialize, or reinitialize, this instance of rand. */
private void initState() {
isaacA = 0;
isaacB = 0;
isaacC = 0;
Arrays.fill(arr, GLD_RATIO);
for (int j = 0; j < 4; j++) {
shuffle();
}
// fill in mem[] with messy stuff
for (int j = 0; j < SIZE; j += 8) {
arr[0] += rsl[j];
arr[1] += rsl[j + 1];
arr[2] += rsl[j + 2];
arr[3] += rsl[j + 3];
arr[4] += rsl[j + 4];
arr[5] += rsl[j + 5];
arr[6] += rsl[j + 6];
arr[7] += rsl[j + 7];
shuffle();
setState(j);
}
// second pass makes all of seed affect all of mem
for (int j = 0; j < SIZE; j += 8) {
arr[0] += mem[j];
arr[1] += mem[j + 1];
arr[2] += mem[j + 2];
arr[3] += mem[j + 3];
arr[4] += mem[j + 4];
arr[5] += mem[j + 5];
arr[6] += mem[j + 6];
arr[7] += mem[j + 7];
shuffle();
setState(j);
}
isaac();
count = SIZE - 1;
}
/** Shuffle array. */
private void shuffle() {
arr[0] ^= arr[1] << 11;
arr[3] += arr[0];
arr[1] += arr[2];
arr[1] ^= arr[2] >>> 2;
arr[4] += arr[1];
arr[2] += arr[3];
arr[2] ^= arr[3] << 8;
arr[5] += arr[2];
arr[3] += arr[4];
arr[3] ^= arr[4] >>> 16;
arr[6] += arr[3];
arr[4] += arr[5];
arr[4] ^= arr[5] << 10;
arr[7] += arr[4];
arr[5] += arr[6];
arr[5] ^= arr[6] >>> 4;
arr[0] += arr[5];
arr[6] += arr[7];
arr[6] ^= arr[7] << 8;
arr[1] += arr[6];
arr[7] += arr[0];
arr[7] ^= arr[0] >>> 9;
arr[2] += arr[7];
arr[0] += arr[1];
}
/** Set the state by copying the internal arrays.
*
* @param start First index into {@link #mem} array.
*/
private void setState(int start) {
mem[start] = arr[0];
mem[start + 1] = arr[1];
mem[start + 2] = arr[2];
mem[start + 3] = arr[3];
mem[start + 4] = arr[4];
mem[start + 5] = arr[5];
mem[start + 6] = arr[6];
mem[start + 7] = arr[7];
}
}