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 /** 20 * A Permuted Congruential Generator (PCG) that is composed of a 64-bit Linear Congruential 21 * Generator (LCG) combined with the XSH-RR (xorshift; random rotate) output 22 * transformation to create 32-bit output. 23 * 24 * <p>State size is 128 bits and the period is 2<sup>64</sup>.</p> 25 * 26 * <p><strong>Note:</strong> Although the seed size is 128 bits, only the first 64 are 27 * effective: in effect, two seeds that only differ by the last 64 bits may produce 28 * highly correlated sequences. 29 * 30 * @see <a href="http://www.pcg-random.org/"> 31 * PCG, A Family of Better Random Number Generators</a> 32 * @since 1.3 33 */ 34 public class PcgXshRr32 extends AbstractPcg6432 { 35 /** 36 * Creates a new instance using a default increment. 37 * 38 * @param seed Initial state. 39 * @since 1.4 40 */ 41 public PcgXshRr32(Long seed) { 42 super(seed); 43 } 44 45 /** 46 * Creates a new instance. 47 * 48 * <p><strong>Note:</strong> Although the seed size is 128 bits, only the first 64 are 49 * effective: in effect, two seeds that only differ by the last 64 bits may produce 50 * highly correlated sequences. 51 * 52 * @param seed Initial seed. 53 * If the length is larger than 2, only the first 2 elements will 54 * be used; if smaller, the remaining elements will be automatically set. 55 * 56 * <p>The 1st element is used to set the LCG state. The 2nd element is used 57 * to set the LCG increment; the most significant bit 58 * is discarded by left shift and the increment is set to odd.</p> 59 */ 60 public PcgXshRr32(long[] seed) { 61 super(seed); 62 } 63 64 /** {@inheritDoc} */ 65 @Override 66 protected int transform(long x) { 67 final int count = (int)(x >>> 59); 68 return Integer.rotateRight((int)((x ^ (x >>> 18)) >>> 27), count); 69 } 70 }