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-RS (xorshift; random shift) 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 PcgXshRs32 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 PcgXshRs32(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 PcgXshRs32(long[] seed) {
61 super(seed);
62 }
63
64 /** {@inheritDoc} */
65 @Override
66 protected int transform(long x) {
67 final int count = (int)(x >>> 61);
68 return (int)((x ^ (x >>> 22)) >>> (22 + count));
69 }
70 }