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 Linear Congruential Generator (LCG) and output 32-bits 24 * 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 AbstractPcg6432 extends IntProvider { 31 /** Size of the seed array. */ 32 private static final int SEED_SIZE = 2; 33 34 /** The state of the LCG. */ 35 private long state; 36 37 /** The increment of the LCG. */ 38 private long increment; 39 40 /** 41 * Creates a new instance. 42 * 43 * @param seed Initial seed. 44 * If the length is larger than 2, only the first 2 elements will 45 * be used; if smaller, the remaining elements will be automatically set. 46 */ 47 AbstractPcg6432(long[] seed) { 48 if (seed.length < SEED_SIZE) { 49 final long[] tmp = new long[SEED_SIZE]; 50 fillState(tmp, seed); 51 setSeedInternal(tmp); 52 } else { 53 setSeedInternal(seed); 54 } 55 } 56 57 /** 58 * Seeds the RNG. 59 * 60 * @param seed Seed. 61 */ 62 private void setSeedInternal(long[] seed) { 63 // Ensure the increment is odd to provide a maximal period LCG. 64 this.increment = (seed[1] << 1) | 1; 65 this.state = bump(seed[0] + this.increment); 66 } 67 68 /** 69 * Provides the next state of the LCG. 70 * 71 * @param input Current state. 72 * @return next state 73 */ 74 private long bump(long input) { 75 return input * 6364136223846793005L + increment; 76 } 77 78 /** {@inheritDoc} */ 79 @Override 80 public int next() { 81 final long x = state; 82 state = bump(state); 83 return transform(x); 84 } 85 86 /** 87 * Transform the 64-bit state of the generator to a 32-bit output. 88 * The transformation function shall vary with respect to different generators. 89 * 90 * @param x State. 91 * @return the output 92 */ 93 protected abstract int transform(long x); 94 95 /** {@inheritDoc} */ 96 @Override 97 protected byte[] getStateInternal() { 98 // The increment is divided by 2 before saving. 99 // This transform is used in the reference PCG code; it prevents restoring from 100 // a byte state a non-odd increment that results in a sub-maximal period generator. 101 return composeStateInternal(NumberFactory.makeByteArray( 102 new long[] {state, increment >>> 1}), 103 super.getStateInternal()); 104 } 105 106 /** {@inheritDoc} */ 107 @Override 108 protected void setStateInternal(byte[] s) { 109 final byte[][] c = splitStateInternal(s, SEED_SIZE * 8); 110 final long[] tempseed = NumberFactory.makeLongArray(c[0]); 111 state = tempseed[0]; 112 // Reverse the transform performed during getState to make the increment odd again. 113 increment = tempseed[1] << 1 | 1; 114 super.setStateInternal(c[1]); 115 } 116 }