001 /**
002 *
003 * Copyright 2004 Protique Ltd
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 **/
018
019 package org.activemq.transport.reliable;
020
021 /**
022 * A Shuffled Multiple Combined Linear Congruential Generator Uses L'Ecuyer's CLCG4 with a Bays-Durham shuffle. From
023 * <cite>Numerical Recipes inC </cite> This produces a more random stream of results than just
024 * <code>java.util.Random</code>
025 *
026 * @version $Revision: 1.1.1.1 $
027 */
028 public class SMLCGRandom {
029 private static final long MULTIPLIER_1 = 40014;
030 private static final long MOD_1 = 2147483563;
031 private static final long MULTIPLIER_2 = 40692;
032 private static final long MOD_2 = 2147483399;
033 private static final int SHUFFLE_LEN = 32;
034 private static final int WARMUP_LENGTH = 19;
035 private int generated_1, generated_2, state;
036 private int[] shuffle;
037
038 /**
039 * Creates a new pseudorandom number generator, seeded from the current time.
040 */
041 public SMLCGRandom() {
042 this(System.currentTimeMillis());
043 }
044
045 /**
046 * Creates the generator with the provided seed
047 *
048 * @param seed
049 */
050 public SMLCGRandom(long seed) {
051 shuffle = new int[SHUFFLE_LEN];
052 this.setSeed(seed);
053 }
054
055 /**
056 * Set the seed for the random generator
057 * @param seed
058 * @throws IllegalArgumentException
059 */
060 public void setSeed(long seed) throws IllegalArgumentException {
061 int i;
062 generated_1 = generated_2 = (int) (seed & 0x7FFFFFFFFL);
063 for (i = 0;i < WARMUP_LENGTH;i++) {
064 generated_1 = (int) ((generated_1 * MULTIPLIER_1) % MOD_1);
065 }
066 for (i = 0;i < SHUFFLE_LEN;i++) {
067 generated_1 = (int) ((generated_1 * MULTIPLIER_1) % MOD_1);
068 shuffle[(SHUFFLE_LEN - 1) - i] = generated_1;
069 }
070 state = shuffle[0];
071 }
072
073 /**
074 * @return the next random, uniformly distrubted, <tt>short</tt> value
075 */
076 public short nextShort() {
077 return (short) ((((short) nextByte()) << 8) | ((short) (nextByte() & 0xFF)));
078 }
079
080 /**
081 * @return the next random, uniformly distrubted, <tt>int</tt> value
082 */
083 public int nextInt() {
084 return (int) ((((int) nextShort()) << 16) | (((int) nextShort()) & 0xFFFF));
085 }
086
087 /**
088 * @return the next random, uniformly distrubted, <tt>long</tt> value
089 */
090 public long nextLong() {
091 return (long) ((((long) nextInt()) << 32) | (((long) nextInt()) & 0xFFFFFFFFl));
092 }
093
094 /**
095 * @return the next random, uniformly distributed, <tt>float</tt> value, greater than or equal to 0 and less than
096 * 1.
097 */
098 public float nextFloat() {
099 return (float) ((nextInt() & 0x7FFFFFFF) / (0x7FFFFFFF * 1.0));
100 }
101
102 /**
103 * @return the next random, uniformly distributed, <tt>double</tt> value, greater than or equal to 0 and less than
104 * 1.
105 */
106 public double nextDouble() {
107 return (double) ((nextLong() & 0x7FFFFFFFFFFFFFFFl) / (0x7FFFFFFFFFFFFFFFl * 1.0));
108 }
109
110 /**
111 * @return the next random, uniformly distrubted, <tt>byte</tt> value
112 */
113 public byte nextByte() {
114 int i = 0;
115 generated_1 = (int) ((generated_1 * MULTIPLIER_1) % MOD_1);
116 generated_2 = (int) ((generated_2 * MULTIPLIER_2) % MOD_2);
117 i = state / (1 + (((int) MOD_1) - 1) / SHUFFLE_LEN);
118 i = Math.abs(i);
119 state = (int) ((((long) shuffle[i]) + generated_2) % MOD_1);
120 shuffle[i] = generated_1;
121 return (byte) (state / (1 + (((int) MOD_1) - 1) / 256));
122 }
123 }