--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/newrandom/RngSupport.java Thu May 23 16:45:56 2019 -0400
@@ -0,0 +1,1018 @@
+/*
+ * 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;
+ }
+
+}
+