View Javadoc
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 WELL19937a 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 Well19937a extends AbstractWell {
35  
36      /** Serializable version identifier. */
37      private static final long serialVersionUID = -7462102162223815419L;
38  
39      /** Number of bits in the pool. */
40      private static final int K = 19937;
41  
42      /** First parameter of the algorithm. */
43      private static final int M1 = 70;
44  
45      /** Second parameter of the algorithm. */
46      private static final int M2 = 179;
47  
48      /** Third parameter of the algorithm. */
49      private static final int M3 = 449;
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 Well19937a() {
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 Well19937a(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 Well19937a(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 Well19937a(long seed) {
78          super(K, M1, M2, M3, seed);
79      }
80  
81      /** {@inheritDoc} */
82      @Override
83      protected int next(final int bits) {
84  
85          final int indexRm1 = iRm1[index];
86          final int indexRm2 = iRm2[index];
87  
88          final int v0       = v[index];
89          final int vM1      = v[i1[index]];
90          final int vM2      = v[i2[index]];
91          final int vM3      = v[i3[index]];
92  
93          final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
94          final int z1 = (v0 ^ (v0 << 25))  ^ (vM1 ^ (vM1 >>> 27));
95          final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
96          final int z3 = z1      ^ z2;
97          final int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));
98  
99          v[index]     = z3;
100         v[indexRm1]  = z4;
101         v[indexRm2] &= 0x80000000;
102         index        = indexRm1;
103 
104         return z4 >>> (32 - bits);
105 
106     }
107 }