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 /**
26 * This class implements the WELL19937c pseudo-random number generator
27 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
28 * <p>
29 * This generator is described in a paper by François Panneton,
30 * Pierre L'Ecuyer and Makoto Matsumoto <a
31 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
32 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
33 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
34 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">
35 * wellrng-errata.txt</a>.
36 *
37 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
38 */
39 public class Well19937c extends AbstractWell {
40
41 /** Serializable version identifier. */
42 private static final long serialVersionUID = 20150223L;
43
44 /** Number of bits in the pool. */
45 private static final int K = 19937;
46
47 /** First parameter of the algorithm. */
48 private static final int M1 = 70;
49
50 /** Second parameter of the algorithm. */
51 private static final int M2 = 179;
52
53 /** Third parameter of the algorithm. */
54 private static final int M3 = 449;
55
56 /** The indirection index table. */
57 private static final IndexTable TABLE = new IndexTable(K, M1, M2, M3);
58
59 /**
60 * Creates a new random number generator.
61 * <p>
62 * The instance is initialized using the current time as the seed.
63 */
64 public Well19937c() {
65 super(K);
66 }
67
68 /**
69 * Creates a new random number generator using a single int seed.
70 * @param seed the initial seed (32 bits integer)
71 */
72 public Well19937c(int seed) {
73 super(K, seed);
74 }
75
76 /**
77 * Creates a new random number generator using an int array seed.
78 * @param seed the initial seed (32 bits integers array), if null
79 * the seed of the generator will be related to the current time
80 */
81 public Well19937c(int[] seed) {
82 super(K, seed);
83 }
84
85 /**
86 * Creates a new random number generator using a single long seed.
87 * @param seed the initial seed (64 bits integer)
88 */
89 public Well19937c(long seed) {
90 super(K, seed);
91 }
92
93 /** {@inheritDoc} */
94 @Override
95 public int nextInt() {
96
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 final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
106 final int z1 = (v0 ^ (v0 << 25)) ^ (vM1 ^ (vM1 >>> 27));
107 final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
108 final int z3 = z1 ^ z2;
109 int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));
110
111 v[index] = z3;
112 v[indexRm1] = z4;
113 v[indexRm2] &= 0x80000000;
114 index = indexRm1;
115
116 // add Matsumoto-Kurita tempering
117 // to get a maximally-equidistributed generator
118 z4 ^= (z4 << 7) & 0xe46e1700;
119 z4 ^= (z4 << 15) & 0x9b868000;
120
121 return z4;
122 }
123
124 }