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 import org.apache.commons.rng.core.util.NumberFactory;
20
21 /**
22 * This abstract class is a base for algorithms from the Permuted Congruential Generator (PCG)
23 * family that use an internal 64-bit Multiplicative Congruential Generator (MCG) and output
24 * 32-bits per cycle.
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 abstract class AbstractPcgMcg6432 extends IntProvider {
31 /** The state of the MCG. */
32 private long state;
33
34 /**
35 * Creates a new instance.
36 *
37 * @param seed Initial seed.
38 */
39 AbstractPcgMcg6432(Long seed) {
40 // A seed of zero will result in a non-functional MCG; it must be odd for a maximal
41 // period MCG. The multiplication factor always sets the 2 least-significant bits to 1
42 // if they are already 1 so these are explicitly set. Bit k (zero-based) will have
43 // period 2^(k-1) starting from bit 2 with a period of 1. Bit 63 has period 2^62.
44 state = seed | 3;
45 }
46
47 /**
48 * Provides the next state of the MCG.
49 *
50 * @param input Current state.
51 * @return next state
52 */
53 private static long bump(long input) {
54 return input * 6364136223846793005L;
55 }
56
57 /** {@inheritDoc} */
58 @Override
59 public int next() {
60 final long x = state;
61 state = bump(state);
62 return transform(x);
63 }
64
65 /**
66 * Transform the 64-bit state of the generator to a 32-bit output.
67 * The transformation function shall vary with respect to different generators.
68 *
69 * @param x State.
70 * @return the output
71 */
72 protected abstract int transform(long x);
73
74 /** {@inheritDoc} */
75 @Override
76 protected byte[] getStateInternal() {
77 return composeStateInternal(NumberFactory.makeByteArray(state),
78 super.getStateInternal());
79 }
80
81 /** {@inheritDoc} */
82 @Override
83 protected void setStateInternal(byte[] s) {
84 final byte[][] d = splitStateInternal(s, 8);
85 // As per the constructor, ensure the lower 2 bits of state are set.
86 state = NumberFactory.makeLong(d[0]) | 3;
87 super.setStateInternal(d[1]);
88 }
89 }