| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.rng.core.source64; |
| |
| import org.apache.commons.rng.core.util.NumberFactory; |
| |
| /** |
| * A Permuted Congruential Generator (PCG) that is composed of a 64-bit Linear Congruential |
| * Generator (LCG) combined with the RXS-M-XS (random xorshift; multiply; xorshift) output |
| * transformation to create 64-bit output. |
| * |
| * <p>State size is 128 bits and the period is 2<sup>64</sup>.</p> |
| * |
| * @see <a href="http://www.pcg-random.org/"> |
| * PCG, A Family of Better Random Number Generators</a> |
| * @since 1.3 |
| */ |
| public class PcgRxsMXs64 extends LongProvider { |
| /** Size of the seed array. */ |
| private static final int SEED_SIZE = 2; |
| /** The default increment. */ |
| private static final long DEFAULT_INCREMENT = 1442695040888963407L; |
| |
| /** The state of the LCG. */ |
| private long state; |
| |
| /** The increment of the LCG. */ |
| private long increment; |
| |
| /** |
| * Creates a new instance using a default increment. |
| * |
| * @param seed Initial state. |
| * @since 1.4 |
| */ |
| public PcgRxsMXs64(Long seed) { |
| increment = DEFAULT_INCREMENT; |
| state = bump(seed + this.increment); |
| } |
| |
| /** |
| * Creates a new instance. |
| * |
| * @param seed Initial seed. |
| * If the length is larger than 2, only the first 2 elements will |
| * be used; if smaller, the remaining elements will be automatically set. |
| * |
| * <p>The 1st element is used to set the LCG state. The 2nd element is used |
| * to set the LCG increment; the most significant bit |
| * is discarded by left shift and the increment is set to odd.</p> |
| */ |
| public PcgRxsMXs64(long[] seed) { |
| if (seed.length < SEED_SIZE) { |
| final long[] tmp = new long[SEED_SIZE]; |
| fillState(tmp, seed); |
| setSeedInternal(tmp); |
| } else { |
| setSeedInternal(seed); |
| } |
| } |
| |
| /** |
| * Seeds the RNG. |
| * |
| * @param seed Seed. |
| */ |
| private void setSeedInternal(long[] seed) { |
| // Ensure the increment is odd to provide a maximal period LCG. |
| this.increment = (seed[1] << 1) | 1; |
| this.state = bump(seed[0] + this.increment); |
| } |
| |
| /** |
| * Provides the next state of the LCG. |
| * |
| * @param input Current state. |
| * @return next state |
| */ |
| private long bump(long input) { |
| return input * 6364136223846793005L + increment; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public long next() { |
| final long x = state; |
| state = bump(state); |
| final long word = ((x >>> ((x >>> 59) + 5)) ^ x) * -5840758589994634535L; |
| return (word >>> 43) ^ word; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| protected byte[] getStateInternal() { |
| // The increment is divided by 2 before saving. |
| // This transform is used in the reference PCG code; it prevents restoring from |
| // a byte state a non-odd increment that results in a sub-maximal period generator. |
| return composeStateInternal(NumberFactory.makeByteArray( |
| new long[] {state, increment >>> 1}), |
| super.getStateInternal()); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| protected void setStateInternal(byte[] s) { |
| final byte[][] c = splitStateInternal(s, SEED_SIZE * 8); |
| final long[] tempseed = NumberFactory.makeLongArray(c[0]); |
| state = tempseed[0]; |
| // Reverse the transform performed during getState to make the increment odd again. |
| increment = tempseed[1] << 1 | 1; |
| super.setStateInternal(c[1]); |
| } |
| } |