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.math.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  * @version $Revision: 1003892 $ $Date: 2010-10-02 23:28:56 +0200 (sam. 02 oct. 2010) $
32  * @since 2.2
33 
34  */
35 public class Well19937a extends AbstractWell {
36 
37     /** Serializable version identifier. */
38     private static final long serialVersionUID = -7462102162223815419L;
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      */
Well19937a()56     public Well19937a() {
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      */
Well19937a(int seed)63     public Well19937a(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      */
Well19937a(int[] seed)71     public Well19937a(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      */
Well19937a(long seed)78     public Well19937a(long seed) {
79         super(K, M1, M2, M3, seed);
80     }
81 
82     /** {@inheritDoc} */
83     @Override
next(final int bits)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         final 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         return z4 >>> (32 - bits);
106 
107     }
108 }
109