src/java.base/share/classes/java/util/random/L64X128MixRandom.java
branchJDK-8193209-branch
changeset 57437 f02ffcb61dce
parent 57436 b0c958c0e6c6
child 57547 56cbdc3ea079
--- a/src/java.base/share/classes/java/util/random/L64X128MixRandom.java	Thu Jun 27 18:02:51 2019 -0300
+++ b/src/java.base/share/classes/java/util/random/L64X128MixRandom.java	Thu Jun 27 18:30:27 2019 -0300
@@ -22,7 +22,8 @@
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */
-package java.util;
+
+package java.util.random;
 
 import java.math.BigInteger;
 import java.util.concurrent.atomic.AtomicLong;
@@ -30,14 +31,14 @@
 /**
  * A generator of uniform pseudorandom values applicable for use in
  * (among other contexts) isolated parallel computations that may
- * generate subtasks.  Class {@code L64X128MixRandom} implements
- * interfaces {@link java.util.Rng} and {@link java.util.SplittableRng},
+ * generate subtasks.  Class {@link L64X128MixRandom} implements
+ * interfaces {@link RandomNumberGenerator} and {@link SplittableRNG},
  * and therefore supports methods for producing pseudorandomly chosen
  * numbers of type {@code int}, {@code long}, {@code float}, and {@code double}
- * as well as creating new split-off {@code L64X128MixRandom} objects,
+ * as well as creating new split-off {@link L64X128MixRandom} objects,
  * with similar usages as for class {@link java.util.SplittableRandom}.
- *
- * <p>Series of generated values pass the TestU01 BigCrush and PractRand test suites
+ * <p>
+ * Series of generated values pass the TestU01 BigCrush and PractRand test suites
  * that measure independence and uniformity properties of random number generators.
  * (Most recently validated with
  * <a href="http://simul.iro.umontreal.ca/testu01/tu01.html">version 1.2.3 of TestU01</a>
@@ -47,47 +48,47 @@
  * These tests validate only the methods for certain
  * types and ranges, but similar properties are expected to hold, at
  * least approximately, for others as well.
- *
- * <p>{@code L64X128MixRandom} is a specific member of the LXM family of algorithms
+ * <p>
+ * {@link L64X128MixRandom} is a specific member of the LXM family of algorithms
  * for pseudorandom number generators.  Every LXM generator consists of two
  * subgenerators; one is an LCG (Linear Congruential Generator) and the other is
  * an Xorshift generator.  Each output of an LXM generator is the sum of one
  * output from each subgenerator, possibly processed by a final mixing function
- * (and {@code L64X128MixRandom} does use a mixing function).
- *
- * <p>The LCG subgenerator for {@code L64X128MixRandom} has an update step of the
+ * (and {@link L64X128MixRandom} does use a mixing function).
+ * <p>
+ * The LCG subgenerator for {@link L64X128MixRandom} has an update step of the
  * form {@code s = m * s + a}, where {@code s}, {@code m}, and {@code a} are all
  * of type {@code long}; {@code s} is the mutable state, the multiplier {@code m}
- * is fixed (the same for all instances of {@code L64X128MixRandom}}) and the addend
+ * is fixed (the same for all instances of {@link L64X128MixRandom}}) and the addend
  * {@code a} is a parameter (a final field of the instance).  The parameter
  * {@code a} is required to be odd (this allows the LCG to have the maximal
  * period, namely 2<sup>64</sup>); therefore there are 2<sup>63</sup> distinct choices
  * of parameter.
- *
- * <p>The Xorshift subgenerator for {@code L64X128MixRandom} is the {@code xoroshiro128} algorithm,
+ * <p>
+ * The Xorshift subgenerator for {@link L64X128MixRandom} is the {@code xoroshiro128} algorithm,
  * version 1.0 (parameters 24, 16, 37), without any final scrambler such as "+" or "**".
  * Its state consists of two {@code long} fields {@code x0} and {@code x1},
  * which can take on any values provided that they are not both zero.
  * The period of this subgenerator is 2<sup>128</sup>-1.
- * 
- * <p> The mixing function for {@code L64X128MixRandom} is the 64-bit "starstar(5,7,9)" function.
- *
- * <p> Because the periods 2<sup>64</sup> and 2<sup>128</sup>-1 of the two subgenerators
- * are relatively prime, the <em>period</em> of any single {@code L64X128MixRandom} object 
+ * <p>
+ * The mixing function for {@link L64X128MixRandom} is the 64-bit "starstar(5,7,9)" function.
+ * <p>
+ * Because the periods 2<sup>64</sup> and 2<sup>128</sup>-1 of the two subgenerators
+ * are relatively prime, the <em>period</em> of any single {@link L64X128MixRandom} object
  * (the length of the series of generated 64-bit values before it repeats) is the product
  * of the periods of the subgenerators, that is, 2<sup>64</sup>(2<sup>128</sup>-1),
  * which is just slightly smaller than 2<sup>192</sup>.  Moreover, if two distinct
- * {@code L64X128MixRandom} objects have different {@code a} parameters, then their
+ * {@link L64X128MixRandom} objects have different {@code a} parameters, then their
  * cycles of produced values will be different.
- *
- * <p>The 64-bit values produced by the {@code nextLong()} method are exactly equidistributed.
- * For any specific instance of {@code L64X128MixRandom}, over the course of its cycle each
+ * <p>
+ * The 64-bit values produced by the {@code nextLong()} method are exactly equidistributed.
+ * For any specific instance of {@link L64X128MixRandom}, over the course of its cycle each
  * of the 2<sup>64</sup> possible {@code long} values will be produced 2<sup>128</sup>-1 times.
  * The values produced by the {@code nextInt()}, {@code nextFloat()}, and {@code nextDouble()}
  * methods are likewise exactly equidistributed.
- *
- * <p>In fact, the 64-bit values produced by the {@code nextLong()} method are 2-equidistributed.
- * To be precise: for any specific instance of {@code L64X128MixRandom}, consider
+ * <p>
+ * In fact, the 64-bit values produced by the {@code nextLong()} method are 2-equidistributed.
+ * To be precise: for any specific instance of {@link L64X128MixRandom}, consider
  * the (overlapping) length-2 subsequences of the cycle of 64-bit values produced by
  * {@code nextLong()} (assuming no other methods are called that would affect the state).
  * There are 2<sup>64</sup>(2<sup>128</sup>-1) such subsequences, and each subsequence,
@@ -98,43 +99,42 @@
  * of the probability of getting one of the less common subsequence values and the
  * probability of getting one of the more common subsequence values is 1-2<sup>-64</sup>.
  * (Note that the set of 2<sup>64</sup> less-common subsequence values will differ from
- * one instance of {@code L64X128MixRandom} to another, as a function of the additive
+ * one instance of {@link L64X128MixRandom} to another, as a function of the additive
  * parameter of the LCG.)  The values produced by the {@code nextInt()}, {@code nextFloat()},
  * and {@code nextDouble()} methods are likewise 2-equidistributed.
- *
- * <p>Method {@link #split} constructs and returns a new {@code L64X128MixRandom}
+ * <p>
+ * Method {@link #split} constructs and returns a new {@link L64X128MixRandom}
  * instance that shares no mutable state with the current instance. However, with
  * very high probability, the values collectively generated by the two objects
  * have the same statistical properties as if the same quantity of values were
- * generated by a single thread using a single {@code L64X128MixRandom} object.
- * This is because, with high probability, distinct {@code L64X128MixRandom} objects
+ * generated by a single thread using a single {@link L64X128MixRandom} object.
+ * This is because, with high probability, distinct {@link L64X128MixRandom} objects
  * have distinct {@code a} parameters and therefore use distinct members of the
  * algorithmic family; and even if their {@code a} parameters are the same, with
  * very high probability they will traverse different parts of their common state
  * cycle.
- *
- * <p>As with {@link java.util.SplittableRandom}, instances of
- * {@code L64X128MixRandom} are <em>not</em> thread-safe.
+ * <p>
+ * As with {@link java.util.SplittableRandom}, instances of
+ * {@link L64X128MixRandom} are <em>not</em> thread-safe.
  * They are designed to be split, not shared, across threads. For
  * example, a {@link java.util.concurrent.ForkJoinTask} fork/join-style
  * computation using random numbers might include a construction
  * of the form {@code new Subtask(someL64X128MixRandom.split()).fork()}.
- *
- * <p>This class provides additional methods for generating random
+ * <p>
+ * This class provides additional methods for generating random
  * streams, that employ the above techniques when used in
  * {@code stream.parallel()} mode.
- *
- * <p>Instances of {@code L64X128MixRandom} are not cryptographically
+ * <p>
+ * Instances of {@link L64X128MixRandom} are not cryptographically
  * secure.  Consider instead using {@link java.security.SecureRandom}
  * in security-sensitive applications. Additionally,
  * default-constructed instances do not use a cryptographically random
  * seed unless the {@linkplain System#getProperty system property}
  * {@code java.util.secureRandomSeed} is set to {@code true}.
  *
- * @author  Guy Steele
- * @since   1.9
+ * @since 14
  */
-public final class L64X128MixRandom extends AbstractSplittableRng {
+public final class L64X128MixRandom extends AbstractSplittableRNG {
 
     /*
      * Implementation Overview.
@@ -145,7 +145,7 @@
      *
      * With extremely high probability, no two generators so chosen
      * will have the same `a` parameter, and testing has indicated
-     * that the values generated by two instances of {@code L64X128MixRandom}
+     * that the values generated by two instances of {@link L64X128MixRandom}
      * will be (approximately) independent if have different values for `a`.
      *
      * The default (no-argument) constructor, in essence, uses
@@ -162,19 +162,19 @@
      * File organization: First static fields, then instance
      * fields, then constructors, then instance methods.
      */
-    
+
     /* ---------------- static fields ---------------- */
 
     /**
      * The seed generator for default constructors.
      */
-    private static final AtomicLong defaultGen = new AtomicLong(RngSupport.initialSeed());
+    private static final AtomicLong defaultGen = new AtomicLong(RNGSupport.initialSeed());
 
     /*
      * The period of this generator, which is (2**128 - 1) * 2**64.
      */
-    private static final BigInteger thePeriod =
-	BigInteger.ONE.shiftLeft(128).subtract(BigInteger.ONE).shiftLeft(64);
+    private static final BigInteger PERIOD =
+        BigInteger.ONE.shiftLeft(128).subtract(BigInteger.ONE).shiftLeft(64);
 
     /*
      * Multiplier used in the LCG portion of the algorithm, taken from
@@ -184,7 +184,7 @@
      * Table 4 (first multiplier for size 2<sup>64</sup>).
      */
 
-    private static final long m = 2862933555777941757L;
+    private static final long M = 2862933555777941757L;
 
     /* ---------------- instance fields ---------------- */
 
@@ -213,66 +213,66 @@
      * @param x1 second word of the initial state for the xorshift generator
      */
     public L64X128MixRandom(long a, long s, long x0, long x1) {
-	// Force a to be odd.
+        // Force a to be odd.
         this.a = a | 1;
         this.s = s;
-	this.x0 = x0;
+        this.x0 = x0;
         this.x1 = x1;
-	// If x0 and x1 are both zero, we must choose nonzero values.
+        // If x0 and x1 are both zero, we must choose nonzero values.
         if ((x0 | x1) == 0) {
-	    // At least one of the two values generated here will be nonzero.
-	    this.x0 = RngSupport.mixStafford13(s += RngSupport.GOLDEN_RATIO_64);
-	    this.x1 = RngSupport.mixStafford13(s + RngSupport.GOLDEN_RATIO_64);
-	}
+            // At least one of the two values generated here will be nonzero.
+            this.x0 = RNGSupport.mixStafford13(s += RNGSupport.GOLDEN_RATIO_64);
+            this.x1 = RNGSupport.mixStafford13(s + RNGSupport.GOLDEN_RATIO_64);
+        }
     }
 
     /**
-     * Creates a new instance of {@code L64X128MixRandom} using the
+     * Creates a new instance of {@link L64X128MixRandom} using the
      * specified {@code long} value as the initial seed. Instances of
-     * {@code L64X128MixRandom} created with the same seed in the same
+     * {@link L64X128MixRandom} created with the same seed in the same
      * program generate identical sequences of values.
      *
      * @param seed the initial seed
      */
     public L64X128MixRandom(long seed) {
-	// Using a value with irregularly spaced 1-bits to xor the seed
-	// argument tends to improve "pedestrian" seeds such as 0 or
-	// other small integers.  We may as well use SILVER_RATIO_64.
-	//
-	// The seed is hashed by mixMurmur64 to produce the `a` parameter.
-	// The seed is hashed by mixStafford13 to produce the initial `x0`,
-	// which will then be used to produce the first generated value.
-	// Then x1 is filled in as if by a SplitMix PRNG with
-	// GOLDEN_RATIO_64 as the gamma value and Stafford13 as the mixer.
-        this(RngSupport.mixMurmur64(seed ^= RngSupport.SILVER_RATIO_64),
-	     1,
-	     RngSupport.mixStafford13(seed),
-	     RngSupport.mixStafford13(seed + RngSupport.GOLDEN_RATIO_64));
+        // Using a value with irregularly spaced 1-bits to xor the seed
+        // argument tends to improve "pedestrian" seeds such as 0 or
+        // other small integers.  We may as well use SILVER_RATIO_64.
+        //
+        // The seed is hashed by mixMurmur64 to produce the `a` parameter.
+        // The seed is hashed by mixStafford13 to produce the initial `x0`,
+        // which will then be used to produce the first generated value.
+        // Then x1 is filled in as if by a SplitMix PRNG with
+        // GOLDEN_RATIO_64 as the gamma value and Stafford13 as the mixer.
+        this(RNGSupport.mixMurmur64(seed ^= RNGSupport.SILVER_RATIO_64),
+             1,
+             RNGSupport.mixStafford13(seed),
+             RNGSupport.mixStafford13(seed + RNGSupport.GOLDEN_RATIO_64));
     }
 
     /**
-     * Creates a new instance of {@code L64X128MixRandom} that is likely to
+     * Creates a new instance of {@link L64X128MixRandom} that is likely to
      * generate sequences of values that are statistically independent
      * of those of any other instances in the current program execution,
      * but may, and typically does, vary across program invocations.
      */
     public L64X128MixRandom() {
-	// Using GOLDEN_RATIO_64 here gives us a good Weyl sequence of values.
-	this(defaultGen.getAndAdd(RngSupport.GOLDEN_RATIO_64));
+        // Using GOLDEN_RATIO_64 here gives us a good Weyl sequence of values.
+        this(defaultGen.getAndAdd(RNGSupport.GOLDEN_RATIO_64));
     }
 
     /**
-     * Creates a new instance of {@code L64X128MixRandom} using the specified array of
-     * initial seed bytes. Instances of {@code L64X128MixRandom} created with the same
+     * Creates a new instance of {@link L64X128MixRandom} using the specified array of
+     * initial seed bytes. Instances of {@link L64X128MixRandom} created with the same
      * seed array in the same program execution generate identical sequences of values.
      *
      * @param seed the initial seed
      */
     public L64X128MixRandom(byte[] seed) {
-	// Convert the seed to 4 long values, of which the last 2 are not all zero.
-	long[] data = RngSupport.convertSeedBytesToLongs(seed, 4, 2);
-	long a = data[0], s = data[1], x0 = data[2], x1 = data[3];
-	// Force a to be odd.
+        // Convert the seed to 4 long values, of which the last 2 are not all zero.
+        long[] data = RNGSupport.convertSeedBytesToLongs(seed, 4, 2);
+        long a = data[0], s = data[1], x0 = data[2], x1 = data[3];
+        // Force a to be odd.
         this.a = a | 1;
         this.s = s;
         this.x0 = x0;
@@ -280,27 +280,28 @@
     }
 
     /* ---------------- public methods ---------------- */
-    
+
     /**
-     * Constructs and returns a new instance of {@code L64X128MixRandom}
+     * Constructs and returns a new instance of {@link L64X128MixRandom}
      * that shares no mutable state with this instance.
      * However, with very high probability, the set of values collectively
      * generated by the two objects has the same statistical properties as if
      * same the quantity of values were generated by a single thread using
-     * a single {@code L64X128MixRandom} object.  Either or both of the two
+     * a single {@link L64X128MixRandom} object.  Either or both of the two
      * objects may be further split using the {@code split} method,
      * and the same expected statistical properties apply to the
      * entire set of generators constructed by such recursive splitting.
      *
-     * @param source a {@code SplittableRng} instance to be used instead
+     * @param source a {@link 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 new instance of {@code L64X128MixRandom}
+     *
+     * @return a new instance of {@link L64X128MixRandom}
      */
-    public L64X128MixRandom split(SplittableRng source) {
-	// Literally pick a new instance "at random".
+    public L64X128MixRandom split(SplittableRNG source) {
+        // Literally pick a new instance "at random".
         return new L64X128MixRandom(source.nextLong(), source.nextLong(),
-				    source.nextLong(), source.nextLong());
+                                    source.nextLong(), source.nextLong());
     }
 
     /**
@@ -308,15 +309,16 @@
      *
      * @return a pseudorandom {@code long} value
      */
-
     public long nextLong() {
-	final long z = s + x0;
-	s = m * s + a;  // LCG
-	long q0 = x0, q1 = x1;
-	{ q1 ^= q0; q0 = Long.rotateLeft(q0, 24); q0 = q0 ^ q1 ^ (q1 << 16); q1 = Long.rotateLeft(q1, 37); }  // xoroshiro128v1_0
-	x0 = q0; x1 = q1;
-	return Long.rotateLeft(z * 5, 7) * 9;  // "starstar" mixing function
+        final long z = s + x0;
+        s = M * s + a;  // LCG
+        long q0 = x0, q1 = x1;
+        { q1 ^= q0; q0 = Long.rotateLeft(q0, 24); q0 = q0 ^ q1 ^ (q1 << 16); q1 = Long.rotateLeft(q1, 37); }  // xoroshiro128v1_0
+        x0 = q0; x1 = q1;
+        return Long.rotateLeft(z * 5, 7) * 9;  // "starstar" mixing function
     }
 
-    public BigInteger period() { return thePeriod; }
+    public BigInteger period() {
+        return PERIOD;
+    }
 }