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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.math.BigInteger;
import java.util.stream.Stream;
/**
* This interface is designed to provide a common protocol for objects
* that generate pseudorandom sequences of numbers (or Boolean values)
* and furthermore can easily <it>jump</it> forward (by a fixed amount)
* to a distant point in the state cycle.
*
* <p>Ideally, all {@code JumpableRng} objects produced by iterative
* jumping from a single original {@code JumpableRng} object are
* statistically independent of one another and individually uniform.
* 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 either
* 2<sup>64</sup> or the square root of its period. Implementors are
* advised to use algorithms whose period is at least 2<sup>127</sup>.
*
* <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 JumpableRng} object, calls its {@code jumps} method exactly
* once, and then parcel out generators from the resulting stream, one
* to each thread. It is generally not a good idea to call {@code jump}
* on a generator that was itself produced by the {@code jumps} method,
* because the result may be a generator identical to another
* generator already produce by that call to the {@code jumps} method.
* For this reason, the return type of the {@code jumps} method is
* {@code Stream<Rng>} rather than {@code Stream<JumpableRng>}, even
* though the actual generator objects in that stream likely do also
* implement the {@code JumpableRng} interface.
*
* <p>An implementation of the {@code JumpableRng} interface must provide
* concrete definitions for the methods {@code nextInt()}, {@code nextLong},
* {@code period()}, {@code copy()}, {@code jump()}, and {@code defaultJumpDistance()}.
* Default implementations are provided for all other methods.
*
* <p>Objects that implement {@code java.util.JumpableRng} 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 JumpableRng extends StreamableRng {
/**
* 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
*/
JumpableRng copy();
/**
* 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.
*/
void jump();
/**
* Returns the distance by which the {@code jump()} method will jump
* forward within the state cycle of this generator object.
*
* @return the default jump distance (as a {@code double} value)
*/
double defaultJumpDistance();
/**
* Returns an effectively unlimited stream of new pseudorandom
* number generators, each of which implements the {@code Rng}
* interface.
*
* @implNote It is permitted to implement this method in a manner
* equivalent to {@code jumps(Long.MAX_VALUE)}.
*
* @implNote The default implementation produces a sequential stream
* that repeatedly calls {@code copy()} and {@code jump()} on this generator,
* and the copies become the generators produced by the stream.
*
* @return a stream of objects that implement the {@code Rng} interface
*/
default Stream<Rng> jumps() {
return Stream.generate(this::copyAndJump).sequential();
}
/**
* Returns a stream producing the given {@code streamSize} number of
* new pseudorandom number generators, each of which implements the
* {@code Rng} interface.
*
* @implNote The default implementation produces a sequential stream
* that repeatedly calls {@code copy()} and {@code jump()} on this generator,
* and the copies become the generators produced by the stream.
*
* @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> jumps(long streamSize) {
return jumps().limit(streamSize);
}
/**
* 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 jumps()}.
*
* @return a stream of objects that implement the {@code Rng} interface
*/
default Stream<Rng> rngs() {
return this.jumps();
}
/**
* 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 jumps(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.jumps(streamSize);
}
/**
* Copy this generator, jump this generator forward, then return the copy.
*/
default Rng copyAndJump() {
Rng result = copy();
jump();
return result;
}
}