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+++ b/newrandom/LeapableRng.java	Thu May 23 16:45:56 2019 -0400
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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.
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ */
+// 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 sequences of pseudorandom numbers (or Boolean values)
+ * and furthermore can easily not only jump but also <it>leap</it> to
+ * a very distant point in the state cycle.
+ *
+ * Typically one will construct a series of {@code LeapableRng} objects
+ * by iterative leaping from a single original {@code LeapableRng}
+ * object, and then for each such object produce a subseries of objects
+ * by iterative jumping.  There is little conceptual difference between
+ * leaping and jumping, but typically a leap will be a very long jump
+ * in the state cycle (perhaps distance 2<sup>128</sup> or so).
+ *
+ * <p>Ideally, all {@code LeapableRng} objects produced by iterative
+ * leaping and jumping from a single original {@code LeapableRng} 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 leaps}
+ * method is used to produce (by jumping) a number of objects no larger
+ * than 2<sup>64</sup>.  Implementors are advised to use algorithms
+ * whose period is at least 2<sup>191</sup>.
+ *
+ * <p>Methods are provided to perform a single leap operation and also
+ * to produce a stream of generators produced from the original by
+ * iterative copying and leaping of internal state.  The generators
+ * produced must implement the {@code JumpableRng} interface but need
+ * not also implement the {@code LeapableRng} interface.  A typical
+ * strategy for a multithreaded application is to create a single
+ * {@code LeapableRng} object, calls its {@code leaps} method exactly
+ * once, and then parcel out generators from the resulting stream, one
+ * to each thread.  Then the {@code jumps} method of each such generator
+ * be called to produce a substream of generator objects.
+ *
+ * <p>An implementation of the {@code LeapableRng} interface must provide
+ * concrete definitions for the methods {@code nextInt()}, {@code nextLong},
+ * {@code period()}, {@code copy()}, {@code jump()}, {@code defaultJumpDistance()},
+ * {@code leap()}, and {@code defaultLeapDistance()}.
+ * Default implementations are provided for all other methods.
+ *
+ * <p>Objects that implement {@code java.util.LeapableRng} 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 LeapableRng extends JumpableRng {
+    /**
+     * 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
+     */
+    LeapableRng copy();
+
+    /**
+     * Alter the state of this pseudorandom number generator so as to
+     * leap forward a large, fixed distance (typically 2<sup>96</sup>
+     * or more) within its state cycle.
+     */
+    void leap();
+    
+    /**
+     * Returns the distance by which the {@code leap()} method will leap
+     * forward within the state cycle of this generator object.
+     *
+     * @return the default leap distance (as a {@code double} value)
+     */
+    double defaultLeapDistance();
+
+    /**
+     * Returns an effectively unlimited stream of new pseudorandom
+     * number generators, each of which implements the {@code JumpableRng}
+     * interface.
+     *
+     * @implNote It is permitted to implement this method in a manner
+     * equivalent to {@code leaps(Long.MAX_VALUE)}.
+     *
+     * @implNote The default implementation produces a sequential stream
+     * that  repeatedly calls {@code copy()} and {@code leap()} on this generator,
+     * and the copies become the generators produced by the stream.
+     *
+     * @return a stream of objects that implement the {@code JumpableRng} interface
+     */
+    default Stream<JumpableRng> leaps() {
+	return Stream.generate(this::copyAndLeap).sequential();
+    }
+
+    /**
+     * Returns a stream producing the given {@code streamSize} number of
+     * new pseudorandom number generators, each of which implements the
+     * {@code JumpableRng} interface.
+     *
+     * @implNote The default implementation produces a sequential stream
+     * that  repeatedly calls {@code copy()} and {@code leap()} 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 JumpableRng} interface
+     * @throws IllegalArgumentException if {@code streamSize} is
+     *         less than zero
+     */
+    default Stream<JumpableRng> leaps(long streamSize) {
+        return leaps().limit(streamSize);
+    }
+        
+    /**
+     * Copy this generator, leap this generator forward, then return the copy.
+     */
+    default JumpableRng copyAndLeap() {
+	JumpableRng result = copy();
+	leap();
+	return result;
+    }
+
+}