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 java.util.Arrays; 20 import org.apache.commons.rng.core.util.NumberFactory; 21 22 /** 23 * Port from Marsaglia's <a href="https://en.wikipedia.org/wiki/Multiply-with-carry"> 24 * "Multiply-With-Carry" algorithm</a>. 25 * 26 * <p> 27 * Implementation is based on the (non-portable!) C code reproduced on 28 * <a href="http://school.anhb.uwa.edu.au/personalpages/kwessen/shared/Marsaglia03.html"> 29 * that page</a>. 30 * </p> 31 * 32 * @see <a href="https://en.wikipedia.org/wiki/Multiply-with-carry">Multiply with carry (Wikipedia)</a> 33 * @since 1.0 34 */ 35 public class MultiplyWithCarry256 extends IntProvider { 36 /** Length of the state array. */ 37 private static final int Q_SIZE = 256; 38 /** Size of the seed. */ 39 private static final int SEED_SIZE = Q_SIZE + 1; 40 /** Multiply. */ 41 private static final long A = 809430660; 42 /** State. */ 43 private final int[] state = new int[Q_SIZE]; 44 /** Current index in "state" array. */ 45 private int index; 46 /** Carry. */ 47 private int carry; 48 49 /** 50 * Creates a new instance. 51 * 52 * @param seed Seed. 53 * If the length is larger than 257, only the first 257 elements will 54 * be used; if smaller, the remaining elements will be automatically 55 * set. 56 */ 57 public MultiplyWithCarry256(int[] seed) { 58 setSeedInternal(seed); 59 } 60 61 /** {@inheritDoc} */ 62 @Override 63 protected byte[] getStateInternal() { 64 final int[] s = Arrays.copyOf(state, SEED_SIZE + 1); 65 s[SEED_SIZE - 1] = carry; 66 s[SEED_SIZE] = index; 67 68 return NumberFactory.makeByteArray(s); 69 } 70 71 /** {@inheritDoc} */ 72 @Override 73 protected void setStateInternal(byte[] s) { 74 checkStateSize(s, (SEED_SIZE + 1) * 4); 75 76 final int[] tmp = NumberFactory.makeIntArray(s); 77 78 System.arraycopy(tmp, 0, state, 0, Q_SIZE); 79 carry = tmp[SEED_SIZE - 1]; 80 index = tmp[SEED_SIZE]; 81 } 82 83 /** 84 * Seeds the RNG. 85 * 86 * @param seed Seed. 87 */ 88 private void setSeedInternal(int[] seed) { 89 // Reset the whole state of this RNG (i.e. "state" and "index"). 90 // Filling procedure is not part of the reference code. 91 final int[] tmp = new int[SEED_SIZE]; 92 fillState(tmp, seed); 93 94 // First element of the "seed" is the initial "carry". 95 final int c = tmp[0]; 96 // Marsaglia's recommendation: 0 <= carry < A. 97 carry = (int) ((c < 0 ? -c : c) % A); 98 99 // Initial state. 100 System.arraycopy(tmp, 1, state, 0, Q_SIZE); 101 102 // Initial index. 103 index = Q_SIZE; 104 } 105 106 /** {@inheritDoc} */ 107 @Override 108 public int next() { 109 if (index == Q_SIZE) { // Whole state used up. 110 // Refill. 111 for (int i = 0; i < Q_SIZE; i++) { 112 final long t = A * (state[i] & 0xffffffffL) + carry; 113 carry = (int) (t >> 32); 114 state[i] = (int) t; 115 } 116 117 // Reset current index. 118 index = 0; 119 } 120 121 return state[index++]; 122 } 123 }