1 /* |
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2 * Copyright (c) 2013, 2019, Oracle and/or its affiliates. All rights reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. Oracle designates this |
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8 * particular file as subject to the "Classpath" exception as provided |
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9 * by Oracle in the LICENSE file that accompanied this code. |
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10 * |
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11 * This code is distributed in the hope that it will be useful, but WITHOUT |
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 * version 2 for more details (a copy is included in the LICENSE file that |
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15 * accompanied this code). |
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16 * |
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17 * You should have received a copy of the GNU General Public License version |
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18 * 2 along with this work; if not, write to the Free Software Foundation, |
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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20 * |
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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22 * or visit www.oracle.com if you need additional information or have any |
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23 * questions. |
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24 */ |
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25 |
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26 package java.util.random; |
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27 |
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28 import java.util.stream.Stream; |
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29 |
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30 /** |
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31 * This interface is designed to provide a common protocol for objects that generate sequences of |
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32 * pseudorandom numbers (or Boolean values) and furthermore can easily not only jump but also |
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33 * <i>leap</i> to a very distant point in the state cycle. |
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34 * <p> |
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35 * Typically one will construct a series of {@link LeapableRNG} objects by iterative leaping from a |
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36 * single original {@link LeapableRNG} object, and then for each such object produce a subseries of |
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37 * objects by iterative jumping. There is little conceptual difference between leaping and jumping, |
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38 * but typically a leap will be a very long jump in the state cycle (perhaps distance |
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39 * 2<sup>128</sup> or so). |
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40 * <p> |
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41 * Ideally, all {@link LeapableRNG} objects produced by iterative leaping and jumping from a single |
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42 * original {@link LeapableRNG} object are statistically independent of one another and individually |
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43 * uniform. In practice, one must settle for some approximation to independence and uniformity. In |
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44 * particular, a specific implementation may assume that each generator in a stream produced by the |
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45 * {@code leaps} method is used to produce (by jumping) a number of objects no larger than |
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46 * 2<sup>64</sup>. Implementors are advised to use algorithms whose period is at least |
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47 * 2<sup>191</sup>. |
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48 * <p> |
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49 * Methods are provided to perform a single leap operation and also to produce a stream of |
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50 * generators produced from the original by iterative copying and leaping of internal state. The |
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51 * generators produced must implement the {@link JumpableRNG} interface but need not also implement |
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52 * the {@link LeapableRNG} interface. A typical strategy for a multithreaded application is to |
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53 * create a single {@link LeapableRNG} object, calls its {@code leaps} method exactly once, and then |
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54 * parcel out generators from the resulting stream, one to each thread. Then the {@code jumps} |
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55 * method of each such generator be called to produce a substream of generator objects. |
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56 * <p> |
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57 * An implementation of the {@link LeapableRNG} interface must provide concrete definitions for the |
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58 * methods {@code nextInt()}, {@code nextLong}, {@code period()}, {@code copy()}, {@code jump()}, |
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59 * {@code defaultJumpDistance()}, {@code leap()}, and {@code defaultLeapDistance()}. Default |
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60 * implementations are provided for all other methods. |
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61 * <p> |
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62 * Objects that implement {@link LeapableRNG} are typically not cryptographically secure. Consider |
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63 * instead using {@link java.security.SecureRandom} to get a cryptographically secure pseudo-random |
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64 * number generator for use by security-sensitive applications. |
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65 * |
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66 * @since 14 |
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67 */ |
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68 public interface LeapableRNG extends JumpableRNG { |
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69 /** |
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70 * Returns a new generator whose internal state is an exact copy of this generator (therefore |
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71 * their future behavior should be identical if subjected to the same series of operations). |
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72 * |
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73 * @return a new object that is a copy of this generator |
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74 */ |
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75 LeapableRNG copy(); |
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76 |
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77 /** |
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78 * Alter the state of this pseudorandom number generator so as to leap forward a large, fixed |
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79 * distance (typically 2<sup>96</sup> or more) within its state cycle. |
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80 */ |
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81 void leap(); |
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82 |
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83 /** |
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84 * Returns the distance by which the {@code leap()} method will leap forward within the state |
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85 * cycle of this generator object. |
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86 * |
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87 * @return the default leap distance (as a {@code double} value) |
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88 */ |
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89 double defaultLeapDistance(); |
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90 |
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91 /** |
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92 * Returns an effectively unlimited stream of new pseudorandom number generators, each of which |
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93 * implements the {@link JumpableRNG} interface. |
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94 * |
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95 * @return a stream of objects that implement the {@link JumpableRNG} interface |
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96 * |
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97 * @implNote It is permitted to implement this method in a manner equivalent to {@code |
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98 * leaps(Long.MAX_VALUE)}. |
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99 * @implNote The default implementation produces a sequential stream that repeatedly |
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100 * calls {@code copy()} and {@code leap()} on this generator, and the copies become the |
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101 * generators produced by the stream. |
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102 */ |
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103 default Stream<JumpableRNG> leaps() { |
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104 return Stream.generate(this::copyAndLeap).sequential(); |
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105 } |
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106 |
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107 /** |
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108 * Returns a stream producing the given {@code streamSize} number of new pseudorandom number |
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109 * generators, each of which implements the {@link JumpableRNG} interface. |
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110 * |
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111 * @param streamSize the number of generators to generate |
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112 * |
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113 * @return a stream of objects that implement the {@link JumpableRNG} interface |
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114 * |
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115 * @throws IllegalArgumentException if {@code streamSize} is less than zero |
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116 * @implNote The default implementation produces a sequential stream that repeatedly |
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117 * calls {@code copy()} and {@code leap()} on this generator, and the copies become the |
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118 * generators produced by the stream. |
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119 */ |
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120 default Stream<JumpableRNG> leaps(long streamSize) { |
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121 return leaps().limit(streamSize); |
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122 } |
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123 |
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124 /** |
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125 * Copy this generator, leap this generator forward, then return the copy. |
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126 * |
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127 * @return a copy of this generator object before the leap occurred |
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128 */ |
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129 default JumpableRNG copyAndLeap() { |
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130 JumpableRNG result = copy(); |
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131 leap(); |
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132 return result; |
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133 } |
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134 |
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135 } |
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