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* Copyright (c) 2016, 2019, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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// package java.util;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
/**
* This interface is designed to provide a common protocol for objects
* that generate sequences of pseudorandom numbers (or Boolean values)
* and furthermore can easily <it>jump</it> to an arbitrarily specified
* distant point in the state cycle.
*
* <p>Ideally, all {@code ArbitrarilyJumpableRng} objects produced by
* iterative jumping from a single original {@code ArbtrarilyJumpableRng}
* object are statistically independent of one another and
* individually uniform, provided that they do not traverse
* overlapping portions of the state cycle. In practice, one must
* settle for some approximation to independence and uniformity. In
* particular, a specific implementation may assume that each
* generator in a stream produced by the {@code jumps} method is used
* to produce a number of values no larger than the jump distance
* specified. Implementors are advised to use algorithms whose period
* is at least 2<sup>127</sup>.
*
* <p>For many applications, it suffices to jump forward by a power of
* two or some small multiple of a power of two, but this power of two
* may not be representable as a {@code long} value. To avoid the
* use of {@code BigInteger} values as jump distances, {@code double}
* values are used instead.
*
* <p>Methods are provided to perform a single jump operation and also
* to produce a stream of generators produced from the original by
* iterative copying and jumping of internal state. A typical
* strategy for a multithreaded application is to create a single
* {@code ArbitrarilyJumpableRng} object, call its {@code jumps}
* method exactly once, and then parcel out generators from the
* resulting stream, one to each thread. However, each generator
* produced also has type {@code ArbitrarilyJumpableRng}; with care,
* different jump distances can be used to traverse the entire
* state cycle in various ways.
*
* <p>An implementation of the {@code ArbitrarilyJumpableRng} interface must
* provide concrete definitions for the methods {@code nextInt()},
* {@code nextLong}, {@code period()}, {@code copy()}, {@code jump(double)},
* {@code defaultJumpDistance()}, and {@code defaultLeapDistance()}.
* Default implementations are provided for all other methods.
* Perhaps the most convenient
* way to implement this interface is to extend the abstract class
* {@link java.util.AbstractArbitrarilyJumpableRng}, which provides
* spliterator-based implementations of the methods {@code ints}, {@code longs},
* {@code doubles}, {@code rngs}, {@code jumps}, and {@code leaps}.
*
* <p>Objects that implement {@code java.util.ArbitrarilyJumpableRng}
* are typically not cryptographically secure. Consider instead using
* {@link java.security.SecureRandom} to get a cryptographically
* secure pseudo-random number generator for use by
* security-sensitive applications.
*
* @author Guy Steele
* @since 1.9
*/
interface ArbitrarilyJumpableRng extends LeapableRng {
/**
* Returns a new generator whose internal state is an exact copy
* of this generator (therefore their future behavior should be
* identical if subjected to the same series of operations).
*
* @return a new object that is a copy of this generator
*/
ArbitrarilyJumpableRng copy();
/**
* Alter the state of this pseudorandom number generator so as to
* jump forward a distance equal to 2<sup>{@code logDistance}</sup>
* within its state cycle.
*
* @param logDistance the base-2 logarithm of the distance to jump
* forward within the state cycle
* @throws IllegalArgumentException if {@code logDistance} is NaN
* or negative, or if 2<sup>{@code logDistance}</sup> is
* greater than the period of this generator
*/
void jumpPowerOfTwo(int logDistance);
/**
* Alter the state of this pseudorandom number generator so as to
* jump forward a specified distance within its state cycle.
*
* @param distance the distance to jump forward within the state cycle
* @throws IllegalArgumentException if {@code distance} is Nan,
* negative, or greater than the period of this generator
*/
void jump(double distance);
/**
* Alter the state of this pseudorandom number generator so as to
* jump forward a large, fixed distance (typically 2<sup>64</sup>
* or more) within its state cycle. The distance used is that
* returned by method {@code defaultJumpDistance()}.
*/
default void jump() { jump(defaultJumpDistance()); }
/**
* Returns an effectively unlimited stream of new pseudorandom
* number generators, each of which implements the {@code ArbitrarilyJumpableRng}
* interface, produced by jumping copies of this generator
* by different integer multiples of the specified jump distance.
*
* @implNote This method is implemented to be equivalent to
* {@code jumps(Long.MAX_VALUE)}.
*
* @param distance a distance to jump forward within the state cycle
* @return a stream of objects that implement the {@code Rng} interface
*/
default Stream<ArbitrarilyJumpableRng> jumps(double distance) {
return Stream.generate(() -> copyAndJump(distance)).sequential();
}
/**
* Returns a stream producing the given {@code streamSize} number of
* new pseudorandom number generators, each of which implements the
* {@code ArbitrarilyJumpableRng} interface, produced by jumping copies of this generator
* by different integer multiples of the specified jump distance.
*
* @param streamSize the number of generators to generate
* @param distance a distance to jump forward within the state cycle
* @return a stream of objects that implement the {@code Rng} interface
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
*/
default Stream<ArbitrarilyJumpableRng> jumps(long streamSize, double distance) {
return jumps(distance).limit(streamSize);
}
/**
* Alter the state of this pseudorandom number generator so as to
* jump forward a very large, fixed distance (typically 2<sup>128</sup>
* or more) within its state cycle. The distance used is that
* returned by method {@code defaultJLeapDistance()}.
*/
default void leap() { jump(defaultLeapDistance()); }
/**
* Copy this generator, jump this generator forward, then return the copy.
*/
default ArbitrarilyJumpableRng copyAndJump(double distance) {
ArbitrarilyJumpableRng result = copy();
jump(distance);
return result;
}
}