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 * https://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
18 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22 package org.hipparchus.random;
23
24 /**
25 * This class implements the WELL44497a pseudo-random number generator
26 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
27 * <p>
28 * This generator is described in a paper by François Panneton,
29 * Pierre L'Ecuyer and Makoto Matsumoto <a
30 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
31 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
32 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
33 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">
34 * wellrng-errata.txt</a>.
35 *
36 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
37 */
38 public class Well44497a extends AbstractWell {
39
40 /** Serializable version identifier. */
41 private static final long serialVersionUID = 20150223L;
42
43 /** Number of bits in the pool. */
44 private static final int K = 44497;
45
46 /** First parameter of the algorithm. */
47 private static final int M1 = 23;
48
49 /** Second parameter of the algorithm. */
50 private static final int M2 = 481;
51
52 /** Third parameter of the algorithm. */
53 private static final int M3 = 229;
54
55 /** The indirection index table. */
56 private static final IndexTable TABLE = new IndexTable(K, M1, M2, M3);
57
58 /**
59 * Creates a new random number generator.
60 * <p>
61 * The instance is initialized using the current time as the seed.
62 */
63 public Well44497a() {
64 super(K);
65 }
66
67 /**
68 * Creates a new random number generator using a single int seed.
69 * @param seed the initial seed (32 bits integer)
70 */
71 public Well44497a(int seed) {
72 super(K, seed);
73 }
74
75 /**
76 * Creates a new random number generator using an int array seed.
77 * @param seed the initial seed (32 bits integers array), if null
78 * the seed of the generator will be related to the current time
79 */
80 public Well44497a(int[] seed) {
81 super(K, seed);
82 }
83
84 /**
85 * Creates a new random number generator using a single long seed.
86 * @param seed the initial seed (64 bits integer)
87 */
88 public Well44497a(long seed) {
89 super(K, seed);
90 }
91
92 /** {@inheritDoc} */
93 @Override
94 public int nextInt() {
95
96 final int indexRm1 = TABLE.getIndexPred(index);
97 final int indexRm2 = TABLE.getIndexPred2(index);
98
99 final int v0 = v[index];
100 final int vM1 = v[TABLE.getIndexM1(index)];
101 final int vM2 = v[TABLE.getIndexM2(index)];
102 final int vM3 = v[TABLE.getIndexM3(index)];
103
104 // the values below include the errata of the original article
105 final int z0 = (0xFFFF8000 & v[indexRm1]) ^ (0x00007FFF & v[indexRm2]);
106 final int z1 = (v0 ^ (v0 << 24)) ^ (vM1 ^ (vM1 >>> 30));
107 final int z2 = (vM2 ^ (vM2 << 10)) ^ (vM3 << 26);
108 final int z3 = z1 ^ z2;
109 final int z2Prime = ((z2 << 9) ^ (z2 >>> 23)) & 0xfbffffff;
110 final int z2Second = ((z2 & 0x00020000) != 0) ? (z2Prime ^ 0xb729fcec) : z2Prime;
111 final int z4 = z0 ^ (z1 ^ (z1 >>> 20)) ^ z2Second ^ z3;
112
113 v[index] = z3;
114 v[indexRm1] = z4;
115 v[indexRm2] &= 0xFFFF8000;
116 index = indexRm1;
117
118 return z4;
119 }
120
121 }