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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    *      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.math3.random;
18  
19  
20  /** This class implements the WELL44497b pseudo-random number generator
21   * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
22  
23   * <p>This generator is described in a paper by Fran&ccedil;ois Panneton,
24   * Pierre L'Ecuyer and Makoto Matsumoto <a
25   * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
26   * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
27   * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
28   * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p>
29  
30   * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
31   * @since 2.2
32  
33   */
34  public class Well44497b extends AbstractWell {
35  
36      /** Serializable version identifier. */
37      private static final long serialVersionUID = 4032007538246675492L;
38  
39      /** Number of bits in the pool. */
40      private static final int K = 44497;
41  
42      /** First parameter of the algorithm. */
43      private static final int M1 = 23;
44  
45      /** Second parameter of the algorithm. */
46      private static final int M2 = 481;
47  
48      /** Third parameter of the algorithm. */
49      private static final int M3 = 229;
50  
51      /** Creates a new random number generator.
52       * <p>The instance is initialized using the current time as the
53       * seed.</p>
54       */
55      public Well44497b() {
56          super(K, M1, M2, M3);
57      }
58  
59      /** Creates a new random number generator using a single int seed.
60       * @param seed the initial seed (32 bits integer)
61       */
62      public Well44497b(int seed) {
63          super(K, M1, M2, M3, seed);
64      }
65  
66      /** Creates a new random number generator using an int array seed.
67       * @param seed the initial seed (32 bits integers array), if null
68       * the seed of the generator will be related to the current time
69       */
70      public Well44497b(int[] seed) {
71          super(K, M1, M2, M3, seed);
72      }
73  
74      /** Creates a new random number generator using a single long seed.
75       * @param seed the initial seed (64 bits integer)
76       */
77      public Well44497b(long seed) {
78          super(K, M1, M2, M3, seed);
79      }
80  
81      /** {@inheritDoc} */
82      @Override
83      protected int next(final int bits) {
84  
85          // compute raw value given by WELL44497a generator
86          // which is NOT maximally-equidistributed
87          final int indexRm1 = iRm1[index];
88          final int indexRm2 = iRm2[index];
89  
90          final int v0       = v[index];
91          final int vM1      = v[i1[index]];
92          final int vM2      = v[i2[index]];
93          final int vM3      = v[i3[index]];
94  
95          // the values below include the errata of the original article
96          final int z0       = (0xFFFF8000 & v[indexRm1]) ^ (0x00007FFF & v[indexRm2]);
97          final int z1       = (v0 ^ (v0 << 24))  ^ (vM1 ^ (vM1 >>> 30));
98          final int z2       = (vM2 ^ (vM2 << 10)) ^ (vM3 << 26);
99          final int z3       = z1      ^ z2;
100         final int z2Prime  = ((z2 << 9) ^ (z2 >>> 23)) & 0xfbffffff;
101         final int z2Second = ((z2 & 0x00020000) != 0) ? (z2Prime ^ 0xb729fcec) : z2Prime;
102         int z4             = z0 ^ (z1 ^ (z1 >>> 20)) ^ z2Second ^ z3;
103 
104         v[index]     = z3;
105         v[indexRm1]  = z4;
106         v[indexRm2] &= 0xFFFF8000;
107         index        = indexRm1;
108 
109         // add Matsumoto-Kurita tempering
110         // to get a maximally-equidistributed generator
111         z4 ^= (z4 <<  7) & 0x93dd1400;
112         z4 ^= (z4 << 15) & 0xfa118000;
113 
114         return z4 >>> (32 - bits);
115 
116     }
117 
118 }