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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 WELL19937c 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   * @version $Id: Well19937c.java 1416643 2012-12-03 19:37:14Z tn $
32   * @since 2.2
33  
34   */
35  public class Well19937c extends AbstractWell {
36  
37      /** Serializable version identifier. */
38      private static final long serialVersionUID = -7203498180754925124L;
39  
40      /** Number of bits in the pool. */
41      private static final int K = 19937;
42  
43      /** First parameter of the algorithm. */
44      private static final int M1 = 70;
45  
46      /** Second parameter of the algorithm. */
47      private static final int M2 = 179;
48  
49      /** Third parameter of the algorithm. */
50      private static final int M3 = 449;
51  
52      /** Creates a new random number generator.
53       * <p>The instance is initialized using the current time as the
54       * seed.</p>
55       */
56      public Well19937c() {
57          super(K, M1, M2, M3);
58      }
59  
60      /** Creates a new random number generator using a single int seed.
61       * @param seed the initial seed (32 bits integer)
62       */
63      public Well19937c(int seed) {
64          super(K, M1, M2, M3, seed);
65      }
66  
67      /** Creates a new random number generator using an int array seed.
68       * @param seed the initial seed (32 bits integers array), if null
69       * the seed of the generator will be related to the current time
70       */
71      public Well19937c(int[] seed) {
72          super(K, M1, M2, M3, seed);
73      }
74  
75      /** Creates a new random number generator using a single long seed.
76       * @param seed the initial seed (64 bits integer)
77       */
78      public Well19937c(long seed) {
79          super(K, M1, M2, M3, seed);
80      }
81  
82      /** {@inheritDoc} */
83      @Override
84      protected int next(final int bits) {
85  
86          final int indexRm1 = iRm1[index];
87          final int indexRm2 = iRm2[index];
88  
89          final int v0       = v[index];
90          final int vM1      = v[i1[index]];
91          final int vM2      = v[i2[index]];
92          final int vM3      = v[i3[index]];
93  
94          final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
95          final int z1 = (v0 ^ (v0 << 25))  ^ (vM1 ^ (vM1 >>> 27));
96          final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
97          final int z3 = z1      ^ z2;
98          int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));
99  
100         v[index]     = z3;
101         v[indexRm1]  = z4;
102         v[indexRm2] &= 0x80000000;
103         index        = indexRm1;
104 
105 
106         // add Matsumoto-Kurita tempering
107         // to get a maximally-equidistributed generator
108         z4 = z4 ^ ((z4 <<  7) & 0xe46e1700);
109         z4 = z4 ^ ((z4 << 15) & 0x9b868000);
110 
111         return z4 >>> (32 - bits);
112 
113     }
114 
115 }