001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.rng.core.source32;
019
020import java.util.Arrays;
021import org.apache.commons.rng.core.util.NumberFactory;
022
023/**
024 * A fast cryptographic pseudo-random number generator.
025 * <p>
026 * ISAAC (Indirection, Shift, Accumulate, Add, and Count) generates 32-bit
027 * random numbers.
028 * ISAAC has been designed to be cryptographically secure and is inspired
029 * by RC4.
030 * Cycles are guaranteed to be at least 2<sup>40</sup> values long, and they
031 * are 2<sup>8295</sup> values long on average.
032 * The results are uniformly distributed, unbiased, and unpredictable unless
033 * you know the seed.
034 * <p>
035 * This code is based (with minor changes and improvements) on the original
036 * implementation of the algorithm by Bob Jenkins.
037 *
038 * @see <a href="http://burtleburtle.net/bob/rand/isaacafa.html">
039 * ISAAC: a fast cryptographic pseudo-random number generator</a>
040 *
041 * @see <a href="https://en.wikipedia.org/wiki/ISAAC_(cipher)">ISAAC (Wikipedia)</a>
042 * @since 1.0
043 */
044public class ISAACRandom extends IntProvider {
045    /** Log of size of rsl[] and mem[]. */
046    private static final int SIZE_L = 8;
047    /** Size of rsl[] and mem[]. */
048    private static final int SIZE = 1 << SIZE_L;
049    /** Half-size of rsl[] and mem[]. */
050    private static final int H_SIZE = SIZE >> 1;
051    /** For pseudo-random lookup. */
052    private static final int MASK = SIZE - 1 << 2;
053    /** The golden ratio. */
054    private static final int GLD_RATIO = 0x9e3779b9;
055    /** The results given to the user. */
056    private final int[] rsl = new int[SIZE];
057    /** The internal state. */
058    private final int[] mem = new int[SIZE];
059    /** Count through the results in rsl[]. */
060    private int count;
061    /** Accumulator. */
062    private int isaacA;
063    /** The last result. */
064    private int isaacB;
065    /** Counter, guarantees cycle is at least 2^40. */
066    private int isaacC;
067    /** Service variable. */
068    private final int[] arr = new int[8];
069    /** Service variable. */
070    private int isaacX;
071    /** Service variable. */
072    private int isaacI;
073    /** Service variable. */
074    private int isaacJ;
075
076    /**
077     * Creates a new ISAAC random number generator.
078     *
079     * @param seed Initial seed
080     */
081    public ISAACRandom(int[] seed) {
082        setSeedInternal(seed);
083    }
084
085    /** {@inheritDoc} */
086    @Override
087    protected byte[] getStateInternal() {
088        final int[] sRsl = Arrays.copyOf(rsl, SIZE);
089        final int[] sMem = Arrays.copyOf(mem, SIZE);
090        final int[] sRem = Arrays.copyOf(new int[] {count, isaacA, isaacB, isaacC}, 4);
091
092        final int[] s = new int[2 * SIZE + sRem.length];
093        System.arraycopy(sRsl, 0, s, 0, SIZE);
094        System.arraycopy(sMem, 0, s, SIZE, SIZE);
095        System.arraycopy(sRem, 0, s, 2 * SIZE, sRem.length);
096
097        return composeStateInternal(NumberFactory.makeByteArray(s),
098                                    super.getStateInternal());
099    }
100
101    /** {@inheritDoc} */
102    @Override
103    protected void setStateInternal(byte[] s) {
104        final byte[][] c = splitStateInternal(s, (2 * SIZE + 4) * 4);
105
106        final int[] tmp = NumberFactory.makeIntArray(c[0]);
107        System.arraycopy(tmp, 0, rsl, 0, SIZE);
108        System.arraycopy(tmp, SIZE, mem, 0, SIZE);
109        final int offset = 2 * SIZE;
110        count = tmp[offset];
111        isaacA = tmp[offset + 1];
112        isaacB = tmp[offset + 2];
113        isaacC = tmp[offset + 3];
114
115        super.setStateInternal(c[1]);
116    }
117
118    /**
119     * Reseeds the RNG.
120     *
121     * @param seed Seed. Cannot be null.
122     */
123    private void setSeedInternal(int[] seed) {
124        final int seedLen = seed.length;
125        final int rslLen = rsl.length;
126        System.arraycopy(seed, 0, rsl, 0, Math.min(seedLen, rslLen));
127        if (seedLen < rslLen) {
128            for (int j = seedLen; j < rslLen; j++) {
129                final long k = rsl[j - seedLen];
130                rsl[j] = (int) (0x6c078965L * (k ^ k >> 30) + j & 0xffffffffL);
131            }
132        }
133        initState();
134    }
135
136    /** {@inheritDoc} */
137    @Override
138    public int next() {
139        if (count < 0) {
140            isaac();
141            count = SIZE - 1;
142        }
143        return rsl[count--];
144    }
145
146    /** Generate 256 results. */
147    private void isaac() {
148        isaacI = 0;
149        isaacJ = H_SIZE;
150        isaacB += ++isaacC;
151        while (isaacI < H_SIZE) {
152            isaac2();
153        }
154        isaacJ = 0;
155        while (isaacJ < H_SIZE) {
156            isaac2();
157        }
158    }
159
160    /** Intermediate internal loop. */
161    private void isaac2() {
162        isaacX = mem[isaacI];
163        isaacA ^= isaacA << 13;
164        isaacA += mem[isaacJ++];
165        isaac3();
166        isaacX = mem[isaacI];
167        isaacA ^= isaacA >>> 6;
168        isaacA += mem[isaacJ++];
169        isaac3();
170        isaacX = mem[isaacI];
171        isaacA ^= isaacA << 2;
172        isaacA += mem[isaacJ++];
173        isaac3();
174        isaacX = mem[isaacI];
175        isaacA ^= isaacA >>> 16;
176        isaacA += mem[isaacJ++];
177        isaac3();
178    }
179
180    /** Lowest level internal loop. */
181    private void isaac3() {
182        mem[isaacI] = mem[(isaacX & MASK) >> 2] + isaacA + isaacB;
183        isaacB = mem[(mem[isaacI] >> SIZE_L & MASK) >> 2] + isaacX;
184        rsl[isaacI++] = isaacB;
185    }
186
187    /** Initialize, or reinitialize, this instance of rand. */
188    private void initState() {
189        isaacA = 0;
190        isaacB = 0;
191        isaacC = 0;
192        Arrays.fill(arr, GLD_RATIO);
193        for (int j = 0; j < 4; j++) {
194            shuffle();
195        }
196        // fill in mem[] with messy stuff
197        for (int j = 0; j < SIZE; j += 8) {
198            arr[0] += rsl[j];
199            arr[1] += rsl[j + 1];
200            arr[2] += rsl[j + 2];
201            arr[3] += rsl[j + 3];
202            arr[4] += rsl[j + 4];
203            arr[5] += rsl[j + 5];
204            arr[6] += rsl[j + 6];
205            arr[7] += rsl[j + 7];
206            shuffle();
207            setState(j);
208        }
209        // second pass makes all of seed affect all of mem
210        for (int j = 0; j < SIZE; j += 8) {
211            arr[0] += mem[j];
212            arr[1] += mem[j + 1];
213            arr[2] += mem[j + 2];
214            arr[3] += mem[j + 3];
215            arr[4] += mem[j + 4];
216            arr[5] += mem[j + 5];
217            arr[6] += mem[j + 6];
218            arr[7] += mem[j + 7];
219            shuffle();
220            setState(j);
221        }
222        isaac();
223        count = SIZE - 1;
224    }
225
226    /** Shuffle array. */
227    private void shuffle() {
228        arr[0] ^= arr[1] << 11;
229        arr[3] += arr[0];
230        arr[1] += arr[2];
231        arr[1] ^= arr[2] >>> 2;
232        arr[4] += arr[1];
233        arr[2] += arr[3];
234        arr[2] ^= arr[3] << 8;
235        arr[5] += arr[2];
236        arr[3] += arr[4];
237        arr[3] ^= arr[4] >>> 16;
238        arr[6] += arr[3];
239        arr[4] += arr[5];
240        arr[4] ^= arr[5] << 10;
241        arr[7] += arr[4];
242        arr[5] += arr[6];
243        arr[5] ^= arr[6] >>> 4;
244        arr[0] += arr[5];
245        arr[6] += arr[7];
246        arr[6] ^= arr[7] << 8;
247        arr[1] += arr[6];
248        arr[7] += arr[0];
249        arr[7] ^= arr[0] >>> 9;
250        arr[2] += arr[7];
251        arr[0] += arr[1];
252    }
253
254    /** Set the state by copying the internal arrays.
255     *
256     * @param start First index into {@link #mem} array.
257     */
258    private void setState(int start) {
259        mem[start] = arr[0];
260        mem[start + 1] = arr[1];
261        mem[start + 2] = arr[2];
262        mem[start + 3] = arr[3];
263        mem[start + 4] = arr[4];
264        mem[start + 5] = arr[5];
265        mem[start + 6] = arr[6];
266        mem[start + 7] = arr[7];
267    }
268}