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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 Fran&ccedil;ois 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 }