/*
* 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;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
import java.util.stream.DoubleStream;
/**
* This interface is designed to provide a common protocol for objects
* that generate sequences of pseudorandom numbers (or Boolean values)
* and furthermore can be <it>split</it> into two objects (the original
* one and a new one) each of which obey that same protocol (and therefore
* can be recursively split indefinitely).
*
* <p>Ideally, all {@code SplittableRNG} objects produced by recursive
* splitting from a single original {@code SplittableRNG} object are
* statistically independent of one another and individually uniform.
* Therefore we would expect the set of values collectively generated
* by a set of such objects to have the same statistical properties as
* if the same quantity of values were generated by a single thread
* using a single {@code SplittableRNG} object. In practice, one must
* settle for some approximation to independence and uniformity.
*
* <p>Methods are provided to perform a single splitting operation and
* also to produce a stream of generators split off from the original
* (by either iterative or recursive splitting, or a combination).
*
* <p>An implementation of the {@code SplittableRng} interface must provide
* concrete definitions for the methods {@code nextInt()}, {@code nextLong},
* {@code period()}, {@code split()}, {@code split(SplittableRng)},
* {@code splits()}, {@code splits(long)}, {@code splits(SplittableRng)},
* and {@code splits(long, SplittableRng)}. Perhaps the most convenient
* way to implement this interface is to extend the abstract class
* {@link java.util.AbstractSplittableRng}.
*
* <p>Objects that implement {@code java.util.SplittableRNG} 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 SplittableRng extends StreamableRng {
/**
* Returns a new pseudorandom number generator, split off from
* this one, that implements the {@code Rng} and {@code SplittableRng}
* interfaces.
*
* This pseudorandom number generator may be used as a source of
* pseudorandom bits used to initialize the state the new one.
*
* @return a new object that implements the {@code Rng} and
* {@code SplittableRng} interfaces
*/
SplittableRng split();
/**
* Returns a new pseudorandom number generator, split off from
* this one, that implements the {@code Rng} and {@code SplittableRng}
* interfaces.
*
* @param source a {@code SplittableRng} instance to be used instead
* of this one as a source of pseudorandom bits used to
* initialize the state of the new ones.
*
* @return an object that implements the {@code Rng} and
* {@code SplittableRng} interfaces
*/
SplittableRng split(SplittableRng source);
/**
* Returns an effectively unlimited stream of new pseudorandom
* number generators, each of which implements the {@code SplittableRng}
* interface.
*
* This pseudorandom number generator may be used as a source of
* pseudorandom bits used to initialize the state the new ones.
*
* @implNote It is permitted to implement this method in a manner
* equivalent to {@code splits(Long.MAX_VALUE)}.
*
* @return a stream of {@code SplittableRng} objects
*/
default Stream<SplittableRng> splits() {
return this.splits(this);
}
/**
* Returns a stream producing the given {@code streamSize} number of
* new pseudorandom number generators, each of which implements the
* {@code SplittableRng} interface.
*
* This pseudorandom number generator may be used as a source of
* pseudorandom bits used to initialize the state the new ones.
*
* @param streamSize the number of values to generate
* @return a stream of {@code SplittableRng} objects
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
*/
Stream<SplittableRng> splits(long streamSize);
/**
* Returns an effectively unlimited stream of new pseudorandom
* number generators, each of which implements the {@code SplittableRng}
* interface.
*
* @implNote It is permitted to implement this method in a manner
* equivalent to {@code splits(Long.MAX_VALUE, source)}.
*
* @param source a {@code SplittableRng} instance to be used instead
* of this one as a source of pseudorandom bits used to
* initialize the state of the new ones.
*
* @return a stream of {@code SplittableRng} objects
*/
Stream<SplittableRng> splits(SplittableRng source);
/**
* Returns a stream producing the given {@code streamSize} number of
* new pseudorandom number generators, each of which implements the
* {@code SplittableRng} interface.
*
* @param streamSize the number of values to generate
* @param source a {@code SplittableRng} instance to be used instead
* of this one as a source of pseudorandom bits used to
* initialize the state of the new ones.
* @return a stream of {@code SplittableRng} objects
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
*/
Stream<SplittableRng> splits(long streamSize, SplittableRng source);
/**
* Returns an effectively unlimited stream of new pseudorandom
* number generators, each of which implements the {@code Rng}
* interface. Ideally the generators in the stream will appear
* to be statistically independent.
*
* @implNote The default implementation calls {@code splits()}.
*
* @return a stream of objects that implement the {@code Rng} interface
*/
default Stream<Rng> rngs() {
return this.splits().map(x -> (Rng)x);
}
/**
* Returns a stream producing the given {@code streamSize} number of
* new pseudorandom number generators, each of which implements the
* {@code Rng} interface. Ideally the generators in the stream will
* appear to be statistically independent.
*
* @implNote The default implementation calls {@code splits(streamSize)}.
*
* @param streamSize the number of generators to generate
* @return a stream of objects that implement the {@code Rng} interface
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
*/
default Stream<Rng> rngs(long streamSize) {
return this.splits(streamSize).map(x -> (Rng)x);
}
}