jdk-sandbox: comparison newrandom/RngSupport.java

equal deleted inserted replaced

-:c646b256fbcc
+:6d87e9f7a1ec
+/*
+* Copyright (c) 2013, 2016, 2019, Oracle and/or its affiliates. All rights reserved.
+* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*
+*/
+// package java.util;
+import java.util.Spliterator;
+import java.util.function.Consumer;
+import java.util.function.IntConsumer;
+import java.util.function.LongConsumer;
+import java.util.function.DoubleConsumer;
+import java.util.stream.StreamSupport;
+import java.util.stream.IntStream;
+import java.util.stream.LongStream;
+import java.util.stream.DoubleStream;
+// import java.util.DoubleZigguratTables;
+/**
+* Low-level utility methods helpful for implementing pseudorandom number generators.
+*
+* This class is mostly for library writers creating specific implementations of the interface {@link java.util.Rng}.
+*
+* @author  Guy Steele
+* @author  Doug Lea
+* @since   1.9
+*/
+public class RngSupport {
+/*
+* Implementation Overview.
+*
+* This class provides utility methods and constants frequently
+* useful in the implentation of pseudorandom number generators
+* that satisfy the interface {@code java.util.Rng}.
+*
+* File organization: First some message strings, then the main
+* public methods, followed by a non-public base spliterator class.
+*/
+// IllegalArgumentException messages
+static final String BadSize = "size must be non-negative";
+static final String BadDistance = "jump distance must be finite, positive, and an exact integer";
+static final String BadBound = "bound must be positive";
+static final String BadFloatingBound = "bound must be finite and positive";
+static final String BadRange = "bound must be greater than origin";
+/* ---------------- public methods ---------------- */
+/**
+* Check a {@code long} proposed stream size for validity.
+*
+* @param streamSize the proposed stream size
+* @throws IllegalArgumentException if {@code streamSize} is negative
+*/
+public static void checkStreamSize(long streamSize) {
+	if (streamSize < 0L)
+throw new IllegalArgumentException(BadSize);
+}
+/**
+* Check a {@code double} proposed jump distance for validity.
+*
+* @param distance the proposed jump distance
+* @throws IllegalArgumentException if {@code size} not positive,
+* finite, and an exact integer
+*/
+public static void checkJumpDistance(double distance) {
+	if (!(distance > 0.0 && distance < Float.POSITIVE_INFINITY && distance == Math.floor(distance)))
+throw new IllegalArgumentException(BadDistance);
+}
+/**
+* Checks a {@code float} upper bound value for validity.
+*
+* @param bound the upper bound (exclusive)
+* @throws IllegalArgumentException if {@code bound} is not
+*         positive and finite
+*/
+public static void checkBound(float bound) {
+	if (!(bound > 0.0 && bound < Float.POSITIVE_INFINITY))
+throw new IllegalArgumentException(BadFloatingBound);
+}
+/**
+* Checks a {@code double} upper bound value for validity.
+*
+* @param bound the upper bound (exclusive)
+* @throws IllegalArgumentException if {@code bound} is not
+*         positive and finite
+*/
+public static void checkBound(double bound) {
+	if (!(bound > 0.0 && bound < Double.POSITIVE_INFINITY))
+throw new IllegalArgumentException(BadFloatingBound);
+}
+/**
+* Checks an {@code int} upper bound value for validity.
+*
+* @param bound the upper bound (exclusive)
+* @throws IllegalArgumentException if {@code bound} is not positive
+*/
+public static void checkBound(int bound) {
+if (bound <= 0)
+throw new IllegalArgumentException(BadBound);
+}
+/**
+* Checks a {@code long} upper bound value for validity.
+*
+* @param bound the upper bound (exclusive)
+* @throws IllegalArgumentException if {@code bound} is not positive
+*/
+public static void checkBound(long bound) {
+if (bound <= 0)
+throw new IllegalArgumentException(BadBound);
+}
+/**
+* Checks a {@code float} range for validity.
+*
+* @param origin the least value (inclusive) in the range
+* @param bound the upper bound (exclusive) of the range
+* @throws IllegalArgumentException unless {@code origin} is finite,
+*         {@code bound} is finite, and {@code bound - origin} is finite
+*/
+public static void checkRange(float origin, float bound) {
+if (!(origin < bound && (bound - origin) < Float.POSITIVE_INFINITY))
+throw new IllegalArgumentException(BadRange);
+}
+/**
+* Checks a {@code double} range for validity.
+*
+* @param origin the least value (inclusive) in the range
+* @param bound the upper bound (exclusive) of the range
+* @throws IllegalArgumentException unless {@code origin} is finite,
+*         {@code bound} is finite, and {@code bound - origin} is finite
+*/
+public static void checkRange(double origin, double bound) {
+if (!(origin < bound && (bound - origin) < Double.POSITIVE_INFINITY))
+throw new IllegalArgumentException(BadRange);
+}
+/**
+* Checks an {@code int} range for validity.
+*
+* @param origin the least value that can be returned
+* @param bound the upper bound (exclusive) for the returned value
+* @throws IllegalArgumentException if {@code origin} is greater than
+*         or equal to {@code bound}
+*/
+public static void checkRange(int origin, int bound) {
+if (origin >= bound)
+throw new IllegalArgumentException(BadRange);
+}
+/**
+* Checks a {@code long} range for validity.
+*
+* @param origin the least value that can be returned
+* @param bound the upper bound (exclusive) for the returned value
+* @throws IllegalArgumentException if {@code origin} is greater than
+*         or equal to {@code bound}
+*/
+public static void checkRange(long origin, long bound) {
+if (origin >= bound)
+throw new IllegalArgumentException(BadRange);
+}
+public static long[] convertSeedBytesToLongs(byte[] seed, int n, int z) {
+	final long[] result = new long[n];
+	final int m = Math.min(seed.length, n << 3);
+	// Distribute seed bytes into the words to be formed.
+	for (int j = 0; j < m; j++) {
+	    result[j>>3] = (result[j>>3] << 8) | seed[j];
+	}
+	// If there aren't enough seed bytes for all the words we need,
+	// use a SplitMix-style PRNG to fill in the rest.
+	long v = result[0];
+	for (int j = (m + 7) >> 3; j < n; j++) {
+	    result[j] = mixMurmur64(v += SILVER_RATIO_64);
+	}
+	// Finally, we need to make sure the last z words are not all zero.
+	search: {
+	    for (int j = n - z; j < n; j++) {
+		if (result[j] != 0) break search;
+	    }
+	    // If they are, fill in using a SplitMix-style PRNG.
+	    // Using "& ~1L" in the next line defends against the case z==1
+	    // by guaranteeing that the first generated value will be nonzero.
+	    long w = result[0] & ~1L;
+	    for (int j = n - z; j < n; j++) {
+		result[j] = mixMurmur64(w += SILVER_RATIO_64);
+	    }
+	}
+	return result;
+}
+public static int[] convertSeedBytesToInts(byte[] seed, int n, int z) {
+	final int[] result = new int[n];
+	final int m = Math.min(seed.length, n << 2);
+	// Distribute seed bytes into the words to be formed.
+	for (int j = 0; j < m; j++) {
+	    result[j>>2] = (result[j>>2] << 8) | seed[j];
+	}
+	// If there aren't enough seed bytes for all the words we need,
+	// use a SplitMix-style PRNG to fill in the rest.
+	int v = result[0];
+	for (int j = (m + 3) >> 2; j < n; j++) {
+	    result[j] = mixMurmur32(v += SILVER_RATIO_32);
+	}
+	// Finally, we need to make sure the last z words are not all zero.
+	search: {
+	    for (int j = n - z; j < n; j++) {
+		if (result[j] != 0) break search;
+	    }
+	    // If they are, fill in using a SplitMix-style PRNG.
+	    // Using "& ~1" in the next line defends against the case z==1
+	    // by guaranteeing that the first generated value will be nonzero.
+	    int w = result[0] & ~1;
+	    for (int j = n - z; j < n; j++) {
+		result[j] = mixMurmur32(w += SILVER_RATIO_32);
+	    }
+	}
+	return result;
+}
+/*
+* Bounded versions of nextX methods used by streams, as well as
+* the public nextX(origin, bound) methods.  These exist mainly to
+* avoid the need for multiple versions of stream spliterators
+* across the different exported forms of streams.
+*/
+/**
+* This is the form of {@code nextLong} used by a {@code LongStream}
+* {@code Spliterator} and by the public method
+* {@code nextLong(origin, bound)}.  If {@code origin} is greater
+* than {@code bound}, then this method simply calls the unbounded
+* version of {@code nextLong()}, choosing pseudorandomly from
+* among all 2<sup>64</sup> possible {@code long} values}, and
+* otherwise uses one or more calls to {@code nextLong()} to
+* choose a value pseudorandomly from the possible values
+* between {@code origin} (inclusive) and {@code bound} (exclusive).
+*
+* @implNote This method first calls {@code nextLong()} to obtain
+* a {@code long} value that is assumed to be pseudorandomly
+* chosen uniformly and independently from the 2<sup>64</sup>
+* possible {@code long} values (that is, each of the 2<sup>64</sup>
+* possible long values is equally likely to be chosen).
+* Under some circumstances (when the specified range is not
+* a power of 2), {@code nextLong()} may be called additional times
+* to ensure that that the values in the specified range are
+* equally likely to be chosen (provided the assumption holds).
+*
+* <p> The implementation considers four cases:
+* <ol>
+*
+* <li> If the {@code} bound} is less than or equal to the {@code origin}
+*      (indicated an unbounded form), the 64-bit {@code long} value
+*      obtained from {@code nextLong()} is returned directly.
+*
+* <li> Otherwise, if the length <it>n</it> of the specified range is an
+*      exact power of two 2<sup><it>m</it></sup> for some integer
+*      <it>m</it>, then return the sum of {@code origin} and the
+*      <it>m</it> lowest-order bits of the value from {@code nextLong()}.
+*
+* <li> Otherwise, if the length <it>n</it> of the specified range
+*      is less than 2<sup>63</sup>, then the basic idea is to use the
+*      remainder modulo <it>n</it> of the value from {@code nextLong()},
+*      but with this approach some values will be over-represented.
+*      Therefore a loop is used to avoid potential bias by rejecting
+*      candidates that are too large.  Assuming that the results from
+*      {@code nextLong()} are truly chosen uniformly and independently,
+*      the expected number of iterations will be somewhere between
+*      1 and 2, depending on the precise value of <it>n</it>.
+*
+* <li> Otherwise, the length <it>n</it> of the specified range
+*      cannot be represented as a positive {@code long} value.
+*      A loop repeatedly calls {@code nextlong()} until obtaining
+*      a suitable candidate,  Again, the expected number of iterations
+*      is less than 2.
+*
+* </ol>
+*
+* @param origin the least value that can be produced,
+*        unless greater than or equal to {@code bound}
+* @param bound the upper bound (exclusive), unless {@code origin}
+*        is greater than or equal to {@code bound}
+* @return a pseudorandomly chosen {@code long} value,
+*         which will be between {@code origin} (inclusive) and
+*         {@code bound} exclusive unless {@code origin}
+*         is greater than or equal to {@code bound}
+*/
+public static long boundedNextLong(Rng rng, long origin, long bound) {
+long r = rng.nextLong();
+if (origin < bound) {
+	    // It's not case (1).
+final long n = bound - origin;
+	    final long m = n - 1;
+if ((n & m) == 0L) {
+		// It is case (2): length of range is a power of 2.
+r = (r & m) + origin;
+	    } else if (n > 0L) {
+		// It is case (3): need to reject over-represented candidates.
+		/* This loop takes an unlovable form (but it works):
+		   because the first candidate is already available,
+		   we need a break-in-the-middle construction,
+		   which is concisely but cryptically performed
+		   within the while-condition of a body-less for loop. */
+for (long u = r >>> 1;            // ensure nonnegative
+u + m - (r = u % n) < 0L;    // rejection check
+u = rng.nextLong() >>> 1) // retry
+;
+r += origin;
+}
+else {
+		// It is case (4): length of range not representable as long.
+while (r < origin || r >= bound)
+r = rng.nextLong();
+}
+}
+return r;
+}
+/**
+* This is the form of {@code nextLong} used by the public method
+* {@code nextLong(bound)}.  This is essentially a version of
+* {@code boundedNextLong(origin, bound)} that has been
+* specialized for the case where the {@code origin} is zero
+* and the {@code bound} is greater than zero.  The value
+* returned is chosen pseudorandomly from nonnegative integer
+* values less than {@code bound}.
+*
+* @implNote This method first calls {@code nextLong()} to obtain
+* a {@code long} value that is assumed to be pseudorandomly
+* chosen uniformly and independently from the 2<sup>64</sup>
+* possible {@code long} values (that is, each of the 2<sup>64</sup>
+* possible long values is equally likely to be chosen).
+* Under some circumstances (when the specified range is not
+* a power of 2), {@code nextLong()} may be called additional times
+* to ensure that that the values in the specified range are
+* equally likely to be chosen (provided the assumption holds).
+*
+* <p> The implementation considers two cases:
+* <ol>
+*
+* <li> If {@code bound} is an exact power of two 2<sup><it>m</it></sup>
+*      for some integer <it>m</it>, then return the sum of {@code origin}
+*      and the <it>m</it> lowest-order bits of the value from
+*      {@code nextLong()}.
+*
+* <li> Otherwise, the basic idea is to use the remainder modulo
+*      <it>bound</it> of the value from {@code nextLong()},
+*      but with this approach some values will be over-represented.
+*      Therefore a loop is used to avoid potential bias by rejecting
+*      candidates that vare too large.  Assuming that the results from
+*      {@code nextLong()} are truly chosen uniformly and independently,
+*      the expected number of iterations will be somewhere between
+*      1 and 2, depending on the precise value of <it>bound</it>.
+*
+* </ol>
+*
+* @param bound the upper bound (exclusive); must be greater than zero
+* @return a pseudorandomly chosen {@code long} value
+*/
+public static long boundedNextLong(Rng rng, long bound) {
+// Specialize boundedNextLong for origin == 0, bound > 0
+final long m = bound - 1;
+long r = rng.nextLong();
+if ((bound & m) == 0L) {
+	    // The bound is a power of 2.
+r &= m;
+	} else {
+	    // Must reject over-represented candidates
+	    /* This loop takes an unlovable form (but it works):
+	       because the first candidate is already available,
+	       we need a break-in-the-middle construction,
+	       which is concisely but cryptically performed
+	       within the while-condition of a body-less for loop. */
+for (long u = r >>> 1;
+u + m - (r = u % bound) < 0L;
+u = rng.nextLong() >>> 1)
+;
+}
+return r;
+}
+/**
+* This is the form of {@code nextInt} used by an {@code IntStream}
+* {@code Spliterator} and by the public method
+* {@code nextInt(origin, bound)}.  If {@code origin} is greater
+* than {@code bound}, then this method simply calls the unbounded
+* version of {@code nextInt()}, choosing pseudorandomly from
+* among all 2<sup>64</sup> possible {@code int} values}, and
+* otherwise uses one or more calls to {@code nextInt()} to
+* choose a value pseudorandomly from the possible values
+* between {@code origin} (inclusive) and {@code bound} (exclusive).
+*
+* @implNote The implementation of this method is identical to
+*     the implementation of {@code nextLong(origin, bound)}
+*     except that {@code int} values and the {@code nextInt()}
+*     method are used rather than {@code long} values and the
+*     {@code nextLong()} method.
+*
+* @param origin the least value that can be produced,
+*        unless greater than or equal to {@code bound}
+* @param bound the upper bound (exclusive), unless {@code origin}
+*        is greater than or equal to {@code bound}
+* @return a pseudorandomly chosen {@code int} value,
+*         which will be between {@code origin} (inclusive) and
+*         {@code bound} exclusive unless {@code origin}
+*         is greater than or equal to {@code bound}
+*/
+public static int boundedNextInt(Rng rng, int origin, int bound) {
+int r = rng.nextInt();
+if (origin < bound) {
+	    // It's not case (1).
+final int n = bound - origin;
+	    final int m = n - 1;
+if ((n & m) == 0) {
+		// It is case (2): length of range is a power of 2.
+r = (r & m) + origin;
+	    } else if (n > 0) {
+		// It is case (3): need to reject over-represented candidates.
+for (int u = r >>> 1;
+u + m - (r = u % n) < 0;
+u = rng.nextInt() >>> 1)
+;
+r += origin;
+}
+else {
+		// It is case (4): length of range not representable as long.
+while (r < origin || r >= bound)
+		    r = rng.nextInt();
+}
+}
+return r;
+}
+/**
+* This is the form of {@code nextInt} used by the public method
+* {@code nextInt(bound)}.  This is essentially a version of
+* {@code boundedNextInt(origin, bound)} that has been
+* specialized for the case where the {@code origin} is zero
+* and the {@code bound} is greater than zero.  The value
+* returned is chosen pseudorandomly from nonnegative integer
+* values less than {@code bound}.
+*
+* @implNote The implementation of this method is identical to
+*     the implementation of {@code nextLong(bound)}
+*     except that {@code int} values and the {@code nextInt()}
+*     method are used rather than {@code long} values and the
+*     {@code nextLong()} method.
+*
+* @param bound the upper bound (exclusive); must be greater than zero
+* @return a pseudorandomly chosen {@code long} value
+*/
+public static int boundedNextInt(Rng rng, int bound) {
+// Specialize boundedNextInt for origin == 0, bound > 0
+final int m = bound - 1;
+int r = rng.nextInt();
+if ((bound & m) == 0) {
+	    // The bound is a power of 2.
+r &= m;
+	} else {
+	    // Must reject over-represented candidates
+for (int u = r >>> 1;
+u + m - (r = u % bound) < 0;
+u = rng.nextInt() >>> 1)
+;
+}
+return r;
+}
+/**
+* This is the form of {@code nextDouble} used by a {@code DoubleStream}
+* {@code Spliterator} and by the public method
+* {@code nextDouble(origin, bound)}.  If {@code origin} is greater
+* than {@code bound}, then this method simply calls the unbounded
+* version of {@code nextDouble()}, and otherwise scales and translates
+* the result of a call to {@code nextDouble()} so that it lies
+* between {@code origin} (inclusive) and {@code bound} (exclusive).
+*
+* @implNote The implementation considers two cases:
+* <ol>
+*
+* <li> If the {@code bound} is less than or equal to the {@code origin}
+*      (indicated an unbounded form), the 64-bit {@code double} value
+*      obtained from {@code nextDouble()} is returned directly.
+*
+* <li> Otherwise, the result of a call to {@code nextDouble} is
+*      multiplied by {@code (bound - origin)}, then {@code origin}
+*      is added, and then if this this result is not less than
+*      {@code bound} (which can sometimes occur because of rounding),
+*      it is replaced with the largest {@code double} value that
+*      is less than {@code bound}.
+*
+* </ol>
+*
+* @param origin the least value that can be produced,
+*        unless greater than or equal to {@code bound}; must be finite
+* @param bound the upper bound (exclusive), unless {@code origin}
+*        is greater than or equal to {@code bound}; must be finite
+* @return a pseudorandomly chosen {@code double} value,
+*         which will be between {@code origin} (inclusive) and
+*         {@code bound} exclusive unless {@code origin}
+*         is greater than or equal to {@code bound},
+*         in which case it will be between 0.0 (inclusive)
+*         and 1.0 (exclusive)
+*/
+public static double boundedNextDouble(Rng rng, double origin, double bound) {
+double r = rng.nextDouble();
+if (origin < bound) {
+r = r * (bound - origin) + origin;
+if (r >= bound)  // may need to correct a rounding problem
+r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
+}
+return r;
+}
+/**
+* This is the form of {@code nextDouble} used by the public method
+* {@code nextDouble(bound)}.  This is essentially a version of
+* {@code boundedNextDouble(origin, bound)} that has been
+* specialized for the case where the {@code origin} is zero
+* and the {@code bound} is greater than zero.
+*
+* @implNote The result of a call to {@code nextDouble} is
+*      multiplied by {@code bound}, and then if this result is
+*      not less than {@code bound} (which can sometimes occur
+*      because of rounding), it is replaced with the largest
+*      {@code double} value that is less than {@code bound}.
+*
+* @param bound the upper bound (exclusive); must be finite and
+*        greater than zero
+* @return a pseudorandomly chosen {@code double} value
+*         between zero (inclusive) and {@code bound} (exclusive)
+*/
+public static double boundedNextDouble(Rng rng, double bound) {
+// Specialize boundedNextDouble for origin == 0, bound > 0
+double r = rng.nextDouble();
+	r = r * bound;
+	if (r >= bound)  // may need to correct a rounding problem
+	    r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
+return r;
+}
+/**
+* This is the form of {@code nextFloat} used by a {@code FloatStream}
+* {@code Spliterator} (if there were any) and by the public method
+* {@code nextFloat(origin, bound)}.  If {@code origin} is greater
+* than {@code bound}, then this method simply calls the unbounded
+* version of {@code nextFloat()}, and otherwise scales and translates
+* the result of a call to {@code nextFloat()} so that it lies
+* between {@code origin} (inclusive) and {@code bound} (exclusive).
+*
+* @implNote The implementation of this method is identical to
+*     the implementation of {@code nextDouble(origin, bound)}
+*     except that {@code float} values and the {@code nextFloat()}
+*     method are used rather than {@code double} values and the
+*     {@code nextDouble()} method.
+*
+* @param origin the least value that can be produced,
+*        unless greater than or equal to {@code bound}; must be finite
+* @param bound the upper bound (exclusive), unless {@code origin}
+*        is greater than or equal to {@code bound}; must be finite
+* @return a pseudorandomly chosen {@code float} value,
+*         which will be between {@code origin} (inclusive) and
+*         {@code bound} exclusive unless {@code origin}
+*         is greater than or equal to {@code bound},
+*         in which case it will be between 0.0 (inclusive)
+*         and 1.0 (exclusive)
+*/
+public static float boundedNextFloat(Rng rng, float origin, float bound) {
+float r = rng.nextFloat();
+if (origin < bound) {
+r = r * (bound - origin) + origin;
+if (r >= bound) // may need to correct a rounding problem
+r = Float.intBitsToFloat(Float.floatToIntBits(bound) - 1);
+}
+return r;
+}
+/**
+* This is the form of {@code nextFloat} used by the public method
+* {@code nextFloat(bound)}.  This is essentially a version of
+* {@code boundedNextFloat(origin, bound)} that has been
+* specialized for the case where the {@code origin} is zero
+* and the {@code bound} is greater than zero.
+*
+* @implNote The implementation of this method is identical to
+*     the implementation of {@code nextDouble(bound)}
+*     except that {@code float} values and the {@code nextFloat()}
+*     method are used rather than {@code double} values and the
+*     {@code nextDouble()} method.
+*
+* @param bound the upper bound (exclusive); must be finite and
+*        greater than zero
+* @return a pseudorandomly chosen {@code float} value
+*         between zero (inclusive) and {@code bound} (exclusive)
+*/
+public static float boundedNextFloat(Rng rng, float bound) {
+// Specialize boundedNextFloat for origin == 0, bound > 0
+float r = rng.nextFloat();
+	r = r * bound;
+	if (r >= bound) // may need to correct a rounding problem
+	    r = Float.intBitsToFloat(Float.floatToIntBits(bound) - 1);
+return r;
+}
+// The following decides which of two strategies initialSeed() will use.
+private static boolean secureRandomSeedRequested() {
+	String pp = java.security.AccessController.doPrivileged(
+new sun.security.action.GetPropertyAction(
+"java.util.secureRandomSeed"));
+	return (pp != null && pp.equalsIgnoreCase("true"));
+}
+private static final boolean useSecureRandomSeed = secureRandomSeedRequested();
+/**
+* Returns a {@code long} value (chosen from some
+* machine-dependent entropy source) that may be useful for
+* initializing a source of seed values for instances of {@code Rng}
+* created by zero-argument constructors.  (This method should
+* <it>not</it> be called repeatedly, once per constructed
+* object; at most it should be called once per class.)
+*
+* @return a {@code long} value, randomly chosen using
+*         appropriate environmental entropy
+*/
+public static long initialSeed() {
+if (useSecureRandomSeed) {
+byte[] seedBytes = java.security.SecureRandom.getSeed(8);
+long s = (long)(seedBytes[0]) & 0xffL;
+for (int i = 1; i < 8; ++i)
+s = (s << 8) | ((long)(seedBytes[i]) & 0xffL);
+return s;
+}
+return (mixStafford13(System.currentTimeMillis()) ^
+mixStafford13(System.nanoTime()));
+}
+/**
+* The fractional part (first 32 or 64 bits, then forced odd) of
+* the golden ratio (1+sqrt(5))/2 and of the silver ratio 1+sqrt(2).
+* Useful for producing good Weyl sequences or as arbitrary nonzero values.
+*/
+public static final int  GOLDEN_RATIO_32 = 0x9e3779b9;
+public static final long GOLDEN_RATIO_64 = 0x9e3779b97f4a7c15L;
+public static final int  SILVER_RATIO_32 = 0x6A09E667;
+public static final long SILVER_RATIO_64 = 0x6A09E667F3BCC909L;
+/**
+* Computes the 64-bit mixing function for MurmurHash3.
+* This is a 64-bit hashing function with excellent avalanche statistics.
+* https://github.com/aappleby/smhasher/wiki/MurmurHash3
+*
+* Note that if the argument {@code z} is 0, the result is 0.
+*
+* @param z any long value
+*
+* @return the result of hashing z
+*/
+public static long mixMurmur64(long z) {
+z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL;
+z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;
+return z ^ (z >>> 33);
+}
+/**
+* Computes Stafford variant 13 of the 64-bit mixing function for MurmurHash3.
+* This is a 64-bit hashing function with excellent avalanche statistics.
+* http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html
+*
+* Note that if the argument {@code z} is 0, the result is 0.
+*
+* @param z any long value
+*
+* @return the result of hashing z
+*/
+public static long mixStafford13(long z) {
+z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L;
+z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
+return z ^ (z >>> 31);
+}
+/**
+* Computes Doug Lea's 64-bit mixing function.
+* This is a 64-bit hashing function with excellent avalanche statistics.
+* It has the advantages of using the same multiplicative constant twice
+* and of using only 32-bit shifts.
+*
+* Note that if the argument {@code z} is 0, the result is 0.
+*
+* @param z any long value
+*
+* @return the result of hashing z
+*/
+public static long mixLea64(long z) {
+z = (z ^ (z >>> 32)) * 0xdaba0b6eb09322e3L;
+z = (z ^ (z >>> 32)) * 0xdaba0b6eb09322e3L;
+return z ^ (z >>> 32);
+}
+/**
+* Computes the 32-bit mixing function for MurmurHash3.
+* This is a 32-bit hashing function with excellent avalanche statistics.
+* https://github.com/aappleby/smhasher/wiki/MurmurHash3
+*
+* Note that if the argument {@code z} is 0, the result is 0.
+*
+* @param z any long value
+*
+* @return the result of hashing z
+*/
+public static int mixMurmur32(int z) {
+z = (z ^ (z >>> 16)) * 0x85ebca6b;
+z = (z ^ (z >>> 13)) * 0xc2b2ae35;
+return z ^ (z >>> 16);
+}
+/**
+* Computes Doug Lea's 32-bit mixing function.
+* This is a 32-bit hashing function with excellent avalanche statistics.
+* It has the advantages of using the same multiplicative constant twice
+* and of using only 16-bit shifts.
+*
+* Note that if the argument {@code z} is 0, the result is 0.
+*
+* @param z any long value
+*
+* @return the result of hashing z
+*/
+public static int mixLea32(int z) {
+z = (z ^ (z >>> 16)) * 0xd36d884b;
+z = (z ^ (z >>> 16)) * 0xd36d884b;
+return z ^ (z >>> 16);
+}
+// Non-public (package only) support for spliterators needed by AbstractSplittableRng
+// and AbstractArbitrarilyJumpableRng and AbstractSharedRng
+/**
+* Base class for making Spliterator classes for streams of randomly chosen values.
+*/
+static abstract class RandomSpliterator {
+long index;
+final long fence;
+	RandomSpliterator(long index, long fence) {
+	    this.index = index; this.fence = fence;
+}
+public long estimateSize() {
+return fence - index;
+}
+public int characteristics() {
+return (Spliterator.SIZED | Spliterator.SUBSIZED |
+Spliterator.NONNULL | Spliterator.IMMUTABLE);
+}
+}
+/*
+* Implementation support for nextExponential() and nextGaussian() methods of Rng.
+*
+* Each is implemented using McFarland's fast modified ziggurat algorithm (largely
+* table-driven, with rare cases handled by computation and rejection sampling).
+* Walker's alias method for sampling a discrete distribution also plays a role.
+*
+* The tables themselves, as well as a number of associated parameters, are defined
+* in class java.util.DoubleZigguratTables, which is automatically generated by the
+* program create_ziggurat_tables.c (which takes only a few seconds to run).
+*
+* For more information about the algorithms, see these articles:
+*
+* Christopher D. McFarland.  2016 (published online 24 Jun 2015).  A modified ziggurat
+* algorithm for generating exponentially and normally distributed pseudorandom numbers.
+* Journal of Statistical Computation and Simulation 86 (7), pages 1281-1294.
+* https://www.tandfonline.com/doi/abs/10.1080/00949655.2015.1060234
+* Also at https://arxiv.org/abs/1403.6870 (26 March 2014).
+*
+* Alastair J. Walker.  1977.  An efficient method for generating discrete random
+* variables with general distributions. ACM Trans. Math. Software 3, 3
+* (September 1977), 253-256. DOI: https://doi.org/10.1145/355744.355749
+*
+* Certain details of these algorithms depend critically on the quality of the
+* low-order bits delivered by NextLong().  These algorithms should not be used
+* with RNG algorithms (such as a simple Linear Congruential Generator) whose
+* low-order output bits do not have good statistical quality.
+*/
+// Implementation support for nextExponential()
+static double computeNextExponential(Rng rng) {
+	long U1 = rng.nextLong();
+	// Experimentation on a variety of machines indicates that it is overall much faster
+	// to do the following & and < operations on longs rather than first cast U1 to int
+	// (but then we need to cast to int before doing the array indexing operation).
+	long i = U1 & DoubleZigguratTables.exponentialLayerMask;
+	if (i < DoubleZigguratTables.exponentialNumberOfLayers) {
+	    // This is the fast path (occurring more than 98% of the time).  Make an early exit.
+	    return DoubleZigguratTables.exponentialX[(int)i] * (U1 >>> 1);
+	}
+	// We didn't use the upper part of U1 after all.  We'll be able to use it later.
+	for (double extra = 0.0; ; ) {
+	    // Use Walker's alias method to sample an (unsigned) integer j from a discrete
+	    // probability distribution that includes the tail and all the ziggurat overhangs;
+	    // j will be less than DoubleZigguratTables.exponentialNumberOfLayers + 1.
+	    long UA = rng.nextLong();
+	    int j = (int)UA & DoubleZigguratTables.exponentialAliasMask;
+	    if (UA >= DoubleZigguratTables.exponentialAliasThreshold[j]) {
+		j = DoubleZigguratTables.exponentialAliasMap[j] & DoubleZigguratTables.exponentialSignCorrectionMask;
+	    }
+	    if (j > 0) {   // Sample overhang j
+		// For the exponential distribution, every overhang is convex.
+		final double[] X = DoubleZigguratTables.exponentialX;
+		final double[] Y = DoubleZigguratTables.exponentialY;
+		for (;; U1 = (rng.nextLong() >>> 1)) {
+		    long U2 = (rng.nextLong() >>> 1);
+		    // Compute the actual x-coordinate of the randomly chosen point.
+		    double x = (X[j] * 0x1.0p63) + ((X[j-1] - X[j]) * (double)U1);
+		    // Does the point lie below the curve?
+		    long Udiff = U2 - U1;
+		    if (Udiff < 0) {
+			// We picked a point in the upper-right triangle.  None of those can be accepted.
+			// So remap the point into the lower-left triangle and try that.
+			// In effect, we swap U1 and U2, and invert the sign of Udiff.
+			Udiff = -Udiff;
+			U2 = U1;
+			U1 -= Udiff;
+		    }
+		    if (Udiff >= DoubleZigguratTables.exponentialConvexMargin) {
+			return x + extra;   // The chosen point is way below the curve; accept it.
+		    }
+		    // Compute the actual y-coordinate of the randomly chosen point.
+		    double y = (Y[j] * 0x1.0p63) + ((Y[j] - Y[j-1]) * (double)U2);
+		    // Now see how that y-coordinate compares to the curve
+		    if (y <= Math.exp(-x)) {
+			return x + extra;   // The chosen point is below the curve; accept it.
+		    }
+		    // Otherwise, we reject this sample and have to try again.
+		}
+	    }
+	    // We are now committed to sampling from the tail.  We could do a recursive call
+	    // and then add X[0] but we save some time and stack space by using an iterative loop.
+	    extra += DoubleZigguratTables.exponentialX0;
+	    // This is like the first five lines of this method, but if it returns, it first adds "extra".
+	    U1 = rng.nextLong();
+	    i = U1 & DoubleZigguratTables.exponentialLayerMask;
+	    if (i < DoubleZigguratTables.exponentialNumberOfLayers) {
+		return DoubleZigguratTables.exponentialX[(int)i] * (U1 >>> 1) + extra;
+	    }
+	}
+}
+// Implementation support for nextGaussian()
+static double computeNextGaussian(Rng rng) {
+	long U1 = rng.nextLong();
+	// Experimentation on a variety of machines indicates that it is overall much faster
+	// to do the following & and < operations on longs rather than first cast U1 to int
+	// (but then we need to cast to int before doing the array indexing operation).
+	long i = U1 & DoubleZigguratTables.normalLayerMask;
+	if (i < DoubleZigguratTables.normalNumberOfLayers) {
+	    // This is the fast path (occurring more than 98% of the time).  Make an early exit.
+	    return DoubleZigguratTables.normalX[(int)i] * U1;   // Note that the sign bit of U1 is used here.
+	}
+	// We didn't use the upper part of U1 after all.
+	// Pull U1 apart into a sign bit and a 63-bit value for later use.
+	double signBit = (U1 >= 0) ? 1.0 : -1.0;
+	U1 = (U1 << 1) >>> 1;
+	// Use Walker's alias method to sample an (unsigned) integer j from a discrete
+	// probability distribution that includes the tail and all the ziggurat overhangs;
+	// j will be less than DoubleZigguratTables.normalNumberOfLayers + 1.
+	long UA = rng.nextLong();
+	int j = (int)UA & DoubleZigguratTables.normalAliasMask;
+	if (UA >= DoubleZigguratTables.normalAliasThreshold[j]) {
+	    j = DoubleZigguratTables.normalAliasMap[j] & DoubleZigguratTables.normalSignCorrectionMask;
+	}
+	double x;
+	// Now the goal is to choose the result, which will be multiplied by signBit just before return.
+// There are four kinds of overhangs:
+	//
+//  j == 0                          :  Sample from tail
+//  0 < j < normalInflectionIndex   :  Overhang is convex; can reject upper-right triangle
+//  j == normalInflectionIndex      :  Overhang includes the inflection point
+//  j > normalInflectionIndex       :  Overhang is concave; can accept point in lower-left triangle
+	//
+// Choose one of four loops to compute x, each specialized for a specific kind of overhang.
+	// Conditional statements are arranged such that the more likely outcomes are first.
+	// In the three cases other than the tail case:
+	// U1 represents a fraction (scaled by 2**63) of the width of rectangle measured from the left.
+	// U2 represents a fraction (scaled by 2**63) of the height of rectangle measured from the top.
+	// Together they indicate a randomly chosen point within the rectangle.
+	final double[] X = DoubleZigguratTables.normalX;
+	final double[] Y = DoubleZigguratTables.normalY;
+	if (j > DoubleZigguratTables.normalInflectionIndex) {   // Concave overhang
+	    for (;; U1 = (rng.nextLong() >>> 1)) {
+		long U2 = (rng.nextLong() >>> 1);
+		// Compute the actual x-coordinate of the randomly chosen point.
+		x = (X[j] * 0x1.0p63) + ((X[j-1] - X[j]) * (double)U1);
+		// Does the point lie below the curve?
+		long Udiff = U2 - U1;
+		if (Udiff >= 0) {
+		    break;   // The chosen point is in the lower-left triangle; accept it.
+		}
+		if (Udiff <= -DoubleZigguratTables.normalConcaveMargin) {
+		    continue;   // The chosen point is way above the curve; reject it.
+		}
+		// Compute the actual y-coordinate of the randomly chosen point.
+		double y = (Y[j] * 0x1.0p63) + ((Y[j] - Y[j-1]) * (double)U2);
+		// Now see how that y-coordinate compares to the curve
+		if (y <= Math.exp(-0.5*x*x)) {
+		    break;   // The chosen point is below the curve; accept it.
+		}
+		// Otherwise, we reject this sample and have to try again.
+}
+	} else if (j == 0) {   // Tail
+	    // Tail-sampling method of Marsaglia and Tsang.  See any one of:
+	    // Marsaglia and Tsang. 1984. A fast, easily implemented method for sampling from decreasing
+	    //    or symmetric unimodal density functions. SIAM J. Sci. Stat. Comput. 5, 349-359.
+	    // Marsaglia and Tsang. 1998. The Monty Python method for generating random variables.
+	    //    ACM Trans. Math. Softw. 24, 3 (September 1998), 341-350.  See page 342, step (4).
+	    //    http://doi.org/10.1145/292395.292453
+	    // Thomas, Luk, Leong, and Villasenor. 2007. Gaussian random number generators.
+	    //    ACM Comput. Surv. 39, 4, Article 11 (November 2007).  See Algorithm 16.
+	    //    http://doi.org/10.1145/1287620.1287622
+	    // Compute two separate random exponential samples and then compare them in certain way.
+	    do {
+		x = (1.0 / DoubleZigguratTables.normalX0) * computeNextExponential(rng);
+	    } while (computeNextExponential(rng) < 0.5*x*x);
+	    x += DoubleZigguratTables.normalX0;
+	} else if (j < DoubleZigguratTables.normalInflectionIndex) {   // Convex overhang
+	    for (;; U1 = (rng.nextLong() >>> 1)) {
+		long U2 = (rng.nextLong() >>> 1);
+		// Compute the actual x-coordinate of the randomly chosen point.
+		x = (X[j] * 0x1.0p63) + ((X[j-1] - X[j]) * (double)U1);
+		// Does the point lie below the curve?
+		long Udiff = U2 - U1;
+		if (Udiff < 0) {
+		    // We picked a point in the upper-right triangle.  None of those can be accepted.
+		    // So remap the point into the lower-left triangle and try that.
+		    // In effect, we swap U1 and U2, and invert the sign of Udiff.
+		    Udiff = -Udiff;
+		    U2 = U1;
+		    U1 -= Udiff;
+		}
+		if (Udiff >= DoubleZigguratTables.normalConvexMargin) {
+		    break;   // The chosen point is way below the curve; accept it.
+		}
+		// Compute the actual y-coordinate of the randomly chosen point.
+		double y = (Y[j] * 0x1.0p63) + ((Y[j] - Y[j-1]) * (double)U2);
+		// Now see how that y-coordinate compares to the curve
+		if (y <= Math.exp(-0.5*x*x)) break;                // The chosen point is below the curve; accept it.
+		// Otherwise, we reject this sample and have to try again.
+	    }
+	} else {
+	    // The overhang includes the inflection point, so the curve is both convex and concave
+	    for (;; U1 = (rng.nextLong() >>> 1)) {
+		long U2 = (rng.nextLong() >>> 1);
+		// Compute the actual x-coordinate of the randomly chosen point.
+		x = (X[j] * 0x1.0p63) + ((X[j-1] - X[j]) * (double)U1);
+		// Does the point lie below the curve?
+		long Udiff = U2 - U1;
+		if (Udiff >= DoubleZigguratTables.normalConvexMargin) {
+		    break;   // The chosen point is way below the curve; accept it.
+		}
+		if (Udiff <= -DoubleZigguratTables.normalConcaveMargin) {
+		    continue;   // The chosen point is way above the curve; reject it.
+		}
+		// Compute the actual y-coordinate of the randomly chosen point.
+		double y = (Y[j] * 0x1.0p63) + ((Y[j] - Y[j-1]) * (double)U2);
+		// Now see how that y-coordinate compares to the curve
+		if (y <= Math.exp(-0.5*x*x)) {
+		    break;   // The chosen point is below the curve; accept it.
+		}
+		// Otherwise, we reject this sample and have to try again.
+	    }
+	}
+	return signBit*x;
+}
+}

branch	briangoetz-test-branch
changeset 57369	6d87e9f7a1ec