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.rng.core.source32;
18  
19  /**
20   * A Permuted Congruential Generator (PCG) that is composed of a 64-bit Linear Congruential
21   * Generator (LCG) combined with the XSH-RR (xorshift; random rotate) output
22   * transformation to create 32-bit output.
23   *
24   * <p>State size is 128 bits and the period is 2<sup>64</sup>.</p>
25   *
26   * <p><strong>Note:</strong> Although the seed size is 128 bits, only the first 64 are
27   * effective: in effect, two seeds that only differ by the last 64 bits may produce
28   * highly correlated sequences.
29   *
30   * @see <a href="http://www.pcg-random.org/">
31   *  PCG, A Family of Better Random Number Generators</a>
32   * @since 1.3
33   */
34  public class PcgXshRr32 extends AbstractPcg6432 {
35      /**
36       * Creates a new instance using a default increment.
37       *
38       * @param seed Initial state.
39       * @since 1.4
40       */
41      public PcgXshRr32(Long seed) {
42          super(seed);
43      }
44  
45      /**
46       * Creates a new instance.
47       *
48       * <p><strong>Note:</strong> Although the seed size is 128 bits, only the first 64 are
49       * effective: in effect, two seeds that only differ by the last 64 bits may produce
50       * highly correlated sequences.
51       *
52       * @param seed Initial seed.
53       * If the length is larger than 2, only the first 2 elements will
54       * be used; if smaller, the remaining elements will be automatically set.
55       *
56       * <p>The 1st element is used to set the LCG state. The 2nd element is used
57       * to set the LCG increment; the most significant bit
58       * is discarded by left shift and the increment is set to odd.</p>
59       */
60      public PcgXshRr32(long[] seed) {
61          super(seed);
62      }
63  
64      /** {@inheritDoc} */
65      @Override
66      protected int transform(long x) {
67          final int count = (int)(x >>> 59);
68          return Integer.rotateRight((int)((x ^ (x >>> 18)) >>> 27), count);
69      }
70  }