1 /*
2 * Copyright (c) 2001-2017, Zoltan Farkas All Rights Reserved.
3 *
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2.1 of the License, or (at your option) any later version.
8 *
9 * This library is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * Additionally licensed with:
19 *
20 * Licensed under the Apache License, Version 2.0 (the "License");
21 * you may not use this file except in compliance with the License.
22 * You may obtain a copy of the License at
23 *
24 * http://www.apache.org/licenses/LICENSE-2.0
25 *
26 * Unless required by applicable law or agreed to in writing, software
27 * distributed under the License is distributed on an "AS IS" BASIS,
28 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
29 * See the License for the specific language governing permissions and
30 * limitations under the License.
31 */
32 package org.spf4j.base;
33
34 import javax.annotation.concurrent.NotThreadSafe;
35 import javax.annotation.concurrent.ThreadSafe;
36
37 /**
38 * @author zoly
39 */
40 public final class IntMath {
41
42 private IntMath() { }
43
44 public static int closestPowerOf2(final int number) {
45 return number == 0 ? 0 : 32 - Integer.numberOfLeadingZeros(number - 1);
46 }
47
48 public static int closestPowerOf2Number(final int number) {
49 return number == 0 ? 0 : 1 << (32 - Integer.numberOfLeadingZeros(number - 1));
50 }
51
52 /**
53 * A very fast Pseudo random generator.
54 * use of this random is appropriate when you need the fastest random that you plan to use in a single
55 * thread.
56 * If you need a thread-safe random, please use JDK ThreadLocalRandom, which will be your best option.
57 */
58 @NotThreadSafe
59 public static final class XorShift32 implements IntSequence {
60 // XorShift128 PRNG with a 2^32-1 period.
61 private int x;
62
63 public XorShift32() {
64 x = (int) System.currentTimeMillis();
65 while (x == 0) {
66 x = (int) System.currentTimeMillis();
67 }
68 }
69
70 @Override
71 public int nextInt() {
72 x ^= (x << 6);
73 x ^= (x >>> 21);
74 return x ^ (x << 7);
75 }
76 }
77
78 /**
79 * @deprecated please use JDK java.util.concurrent.ThreadLocalRandom instead.
80 * The JDK implementation uses local fields in the Thread class instead of a classic ThreadLocal,
81 * which makes it faster...
82 */
83 @ThreadSafe
84 @Deprecated
85 public static final class XorShift32ThreadSafe implements IntSequence {
86
87 private final ThreadLocal<XorShift32> rnd = new ThreadLocalRandom();
88
89 public static final class Singleton {
90
91 public static final XorShift32ThreadSafe INSTANCE = new XorShift32ThreadSafe();
92
93 }
94
95 @Override
96 public int nextInt() {
97 return rnd.get().nextInt();
98 }
99
100 private static class ThreadLocalRandom extends ThreadLocal<XorShift32> {
101
102 @Override
103 protected XorShift32 initialValue() {
104 return new XorShift32();
105 }
106 }
107 }
108
109
110 @NotThreadSafe
111 public static final class XorShift128 implements IntSequence {
112 // XorShift128 PRNG with a 2^128-1 period.
113 private int x = System.identityHashCode(this);
114 private int y = -938745813;
115 private int z = 452465366;
116 private int w = 1343246171;
117
118 @Override
119 public int nextInt() {
120 int t = x ^ (x << 15);
121 x = y; y = z; z = w;
122 w = (w ^ (w >>> 21)) ^ (t ^ (t >>> 4));
123 return w;
124 }
125 }
126
127
128 }