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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.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   * @see <a href="http://www.pcg-random.org/">
27   *  PCG, A Family of Better Random Number Generators</a>
28   * @since 1.3
29   */
30  public class PcgXshRr32 extends AbstractPcg6432 {
31      /**
32       * Creates a new instance.
33       *
34       * @param seed Initial seed.
35       * If the length is larger than 2, only the first 2 elements will
36       * be used; if smaller, the remaining elements will be automatically set.
37       */
38      public PcgXshRr32(long[] seed) {
39          super(seed);
40      }
41  
42      /** {@inheritDoc} */
43      @Override
44      protected int transform(long x) {
45          final int count = (int)(x >>> 59);
46          return Integer.rotateRight((int)((x ^ (x >>> 18)) >>> 27), count);
47      }
48  }