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 }