001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. 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 */ 017package org.apache.commons.rng.core.source32; 018 019/** 020 * A Permuted Congruential Generator (PCG) that is composed of a 64-bit Linear Congruential 021 * Generator (LCG) combined with the XSH-RR (xorshift; random rotate) output 022 * transformation to create 32-bit output. 023 * 024 * <p>State size is 128 bits and the period is 2<sup>64</sup>.</p> 025 * 026 * <p><strong>Note:</strong> Although the seed size is 128 bits, only the first 64 are 027 * effective: in effect, two seeds that only differ by the last 64 bits may produce 028 * highly correlated sequences. 029 * 030 * @see <a href="http://www.pcg-random.org/"> 031 * PCG, A Family of Better Random Number Generators</a> 032 * @since 1.3 033 */ 034public class PcgXshRr32 extends AbstractPcg6432 { 035 /** 036 * Creates a new instance using a default increment. 037 * 038 * @param seed Initial state. 039 * @since 1.4 040 */ 041 public PcgXshRr32(Long seed) { 042 super(seed); 043 } 044 045 /** 046 * Creates a new instance. 047 * 048 * <p><strong>Note:</strong> Although the seed size is 128 bits, only the first 64 are 049 * effective: in effect, two seeds that only differ by the last 64 bits may produce 050 * highly correlated sequences. 051 * 052 * @param seed Initial seed. 053 * If the length is larger than 2, only the first 2 elements will 054 * be used; if smaller, the remaining elements will be automatically set. 055 * 056 * <p>The 1st element is used to set the LCG state. The 2nd element is used 057 * to set the LCG increment; the most significant bit 058 * is discarded by left shift and the increment is set to odd.</p> 059 */ 060 public PcgXshRr32(long[] seed) { 061 super(seed); 062 } 063 064 /** {@inheritDoc} */ 065 @Override 066 protected int transform(long x) { 067 final int count = (int)(x >>> 59); 068 return Integer.rotateRight((int)((x ^ (x >>> 18)) >>> 27), count); 069 } 070}