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 composeStateInternal(NumberFactory.makeByteArray(s), 69 super.getStateInternal()); 70 } 71 72 /** {@inheritDoc} */ 73 @Override 74 protected void setStateInternal(byte[] s) { 75 final byte[][] c = splitStateInternal(s, (SEED_SIZE + 1) * 4); 76 77 final int[] tmp = NumberFactory.makeIntArray(c[0]); 78 79 System.arraycopy(tmp, 0, state, 0, Q_SIZE); 80 carry = tmp[SEED_SIZE - 1]; 81 index = tmp[SEED_SIZE]; 82 83 super.setStateInternal(c[1]); 84 } 85 86 /** 87 * Seeds the RNG. 88 * 89 * @param seed Seed. 90 */ 91 private void setSeedInternal(int[] seed) { 92 // Reset the whole state of this RNG (i.e. "state" and "index"). 93 // Filling procedure is not part of the reference code. 94 final int[] tmp = new int[SEED_SIZE]; 95 fillState(tmp, seed); 96 97 // First element of the "seed" is the initial "carry". 98 final int c = tmp[0]; 99 // Marsaglia's recommendation: 0 <= carry < A. 100 carry = (int) (Math.abs(c) % A); 101 102 // Initial state. 103 System.arraycopy(tmp, 1, state, 0, Q_SIZE); 104 105 // Initial index. 106 index = Q_SIZE; 107 } 108 109 /** {@inheritDoc} */ 110 @Override 111 public int next() { 112 // Produce an index in the range 0-255 113 index &= 0xff; 114 final long t = A * (state[index] & 0xffffffffL) + carry; 115 carry = (int) (t >> 32); 116 return state[index++] = (int) t; 117 } 118 }