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 /** This class implements the WELL44497b pseudo-random number generator
25 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
26 * <p>
27 * This generator is described in a paper by François Panneton,
28 * Pierre L'Ecuyer and Makoto Matsumoto <a
29 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
30 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
31 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
32 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">
33 * wellrng-errata.txt</a>.
34 *
35 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
36 */
37 public class Well44497b extends AbstractWell {
38
39 /** Serializable version identifier. */
40 private static final long serialVersionUID = 20150223L;
41
42 /** Number of bits in the pool. */
43 private static final int K = 44497;
44
45 /** First parameter of the algorithm. */
46 private static final int M1 = 23;
47
48 /** Second parameter of the algorithm. */
49 private static final int M2 = 481;
50
51 /** Third parameter of the algorithm. */
52 private static final int M3 = 229;
53
54 /** The indirection index table. */
55 private static final IndexTable TABLE = new IndexTable(K, M1, M2, M3);
56
57 /**
58 * Creates a new random number generator.
59 * <p>
60 * The instance is initialized using the current time as the seed.
61 */
62 public Well44497b() {
63 super(K);
64 }
65
66 /**
67 * Creates a new random number generator using a single int seed.
68 * @param seed the initial seed (32 bits integer)
69 */
70 public Well44497b(int seed) {
71 super(K, seed);
72 }
73
74 /**
75 * Creates a new random number generator using an int array seed.
76 * @param seed the initial seed (32 bits integers array), if null
77 * the seed of the generator will be related to the current time
78 */
79 public Well44497b(int[] seed) {
80 super(K, seed);
81 }
82
83 /**
84 * Creates a new random number generator using a single long seed.
85 * @param seed the initial seed (64 bits integer)
86 */
87 public Well44497b(long seed) {
88 super(K, seed);
89 }
90
91 /** {@inheritDoc} */
92 @Override
93 public int nextInt() {
94
95 // compute raw value given by WELL44497a generator
96 // which is NOT maximally-equidistributed
97 final int indexRm1 = TABLE.getIndexPred(index);
98 final int indexRm2 = TABLE.getIndexPred2(index);
99
100 final int v0 = v[index];
101 final int vM1 = v[TABLE.getIndexM1(index)];
102 final int vM2 = v[TABLE.getIndexM2(index)];
103 final int vM3 = v[TABLE.getIndexM3(index)];
104
105 // the values below include the errata of the original article
106 final int z0 = (0xFFFF8000 & v[indexRm1]) ^ (0x00007FFF & v[indexRm2]);
107 final int z1 = (v0 ^ (v0 << 24)) ^ (vM1 ^ (vM1 >>> 30));
108 final int z2 = (vM2 ^ (vM2 << 10)) ^ (vM3 << 26);
109 final int z3 = z1 ^ z2;
110 final int z2Prime = ((z2 << 9) ^ (z2 >>> 23)) & 0xfbffffff;
111 final int z2Second = ((z2 & 0x00020000) != 0) ? (z2Prime ^ 0xb729fcec) : z2Prime;
112 int z4 = z0 ^ (z1 ^ (z1 >>> 20)) ^ z2Second ^ z3;
113
114 v[index] = z3;
115 v[indexRm1] = z4;
116 v[indexRm2] &= 0xFFFF8000;
117 index = indexRm1;
118
119 // add Matsumoto-Kurita tempering
120 // to get a maximally-equidistributed generator
121 z4 ^= (z4 << 7) & 0x93dd1400;
122 z4 ^= (z4 << 15) & 0xfa118000;
123
124 return z4;
125 }
126
127 }