1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.rng.core.source32;
18
19 /**
20 * This class implements the WELL19937a pseudo-random number generator
21 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
22 * <p>
23 * This generator is described in a paper by François Panneton,
24 * Pierre L'Ecuyer and Makoto Matsumoto
25 * <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">
26 * Improved Long-Period Generators Based on Linear Recurrences Modulo 2</a>
27 * ACM Transactions on Mathematical Software, 32, 1 (2006).
28 * The errata for the paper are in
29 * <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.
30 * </p>
31 *
32 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
33 * @since 1.0
34 */
35 public class Well19937a extends AbstractWell {
36 /** Number of bits in the pool. */
37 private static final int K = 19937;
38 /** First parameter of the algorithm. */
39 private static final int M1 = 70;
40 /** Second parameter of the algorithm. */
41 private static final int M2 = 179;
42 /** Third parameter of the algorithm. */
43 private static final int M3 = 449;
44 /** The indirection index table. */
45 private static final IndexTable TABLE = new IndexTable(K, M1, M2, M3);
46
47 /**
48 * Creates a new random number generator.
49 *
50 * @param seed Initial seed.
51 */
52 public Well19937a(int[] seed) {
53 super(K, seed);
54 }
55
56 /** {@inheritDoc} */
57 @Override
58 public int next() {
59 final int indexRm1 = TABLE.getIndexPred(index);
60 final int indexRm2 = TABLE.getIndexPred2(index);
61
62 final int v0 = v[index];
63 final int vM1 = v[TABLE.getIndexM1(index)];
64 final int vM2 = v[TABLE.getIndexM2(index)];
65 final int vM3 = v[TABLE.getIndexM3(index)];
66
67 final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
68 final int z1 = (v0 ^ (v0 << 25)) ^ (vM1 ^ (vM1 >>> 27));
69 final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
70 final int z3 = z1 ^ z2;
71 final int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));
72
73 v[index] = z3;
74 v[indexRm1] = z4;
75 v[indexRm2] &= 0x80000000;
76 index = indexRm1;
77
78 return z4;
79 }
80 }