jdk-sandbox: comparison src/java.base/share/classes/java/util/random/L64X128MixRandom.java

equal deleted inserted replaced

-:7e791393cc4d
+:1b314be4feb2
 package java.util.random;
 import java.math.BigInteger;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.random.RandomGenerator.SplittableGenerator;
-import java.util.random.RandomSupport.AbstractSplittableGenerator;
+import java.util.random.RandomSupport.AbstractSplittableWithBrineGenerator;
 /**
 * A generator of uniform pseudorandom values applicable for use in
 * (among other contexts) isolated parallel computations that may
 * generate subtasks.  Class {@link L64X128MixRandom} implements
 * least approximately, for others as well.
 * <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
+* an Xorshift generator.  Each output of an LXM generator is the result of
-* output from each subgenerator, possibly processed by a final mixing function
+* combining state from the LCG with state from the Xorshift generator by
-* (and {@link L64X128MixRandom} does use a mixing function).
+* using a Mixing function (and then the state of the LCG and the state of the
+* Xorshift generator are advanced).
 * <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 {@link L64X128MixRandom}}) and the addend
 * 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 {@link L64X128MixRandom} is the 64-bit "starstar(5,7,9)" function.
+* The mixing function for {@link L64X128MixRandom} is {@link RandomSupport.mixLea64}
+* applied to the argument {@code (s + x0)}.
 * <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),
 * There are 2<sup>64</sup>(2<sup>128</sup>-1) such subsequences, and each subsequence,
 * which consists of 2 64-bit values, can have one of 2<sup>128</sup> values. Of those
 * 2<sup>128</sup> subsequence values, nearly all of them (2<sup>128</sup>-2<sup>64</sup>)
 * occur 2<sup>64</sup> times over the course of the entire cycle, and the other
 * 2<sup>64</sup> subsequence values occur only 2<sup>64</sup>-1 times.  So the ratio
-* of the probability of getting one of the less common subsequence values and the
+* of the probability of getting any specific 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>.
+* probability of getting any specific 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 {@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>
 * seed unless the {@linkplain System#getProperty system property}
 * {@code java.util.secureRandomSeed} is set to {@code true}.
 *
 * @since 14
 */
-public final class L64X128MixRandom extends AbstractSplittableGenerator {
+public final class L64X128MixRandom extends AbstractSplittableWithBrineGenerator {
 /*
 * Implementation Overview.
 *
 * The split operation uses the current generator to choose four new 64-bit
 */
 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
+* Multiplier used in the LCG portion of the algorithm.
-* Pierre L'Ecuyer, Tables of linear congruential generators of
+* Chosen based on research by Sebastiano Vigna and Guy Steele (2019).
-* different sizes and good lattice structure, <em>Mathematics of
+* The spectral scores for dimensions 2 through 8 for the multiplier 0xd1342543de82ef95
-* Computation</em> 68, 225 (January 1999), pages 249-260,
+* are [0.958602, 0.937479, 0.870757, 0.822326, 0.820405, 0.813065, 0.760215].
-* Table 4 (first multiplier for size 2<sup>64</sup>).
+*/
-*/
+private static final long M = 0xd1342543de82ef95L;
-private static final long M = 2862933555777941757L;
 /* ---------------- instance fields ---------------- */
 /**
 * The parameter that is used as an additive constant for the LCG.
 this.s = s;
 this.x0 = x0;
 this.x1 = x1;
 // If x0 and x1 are both zero, we must choose nonzero values.
 if ((x0 | x1) == 0) {
+	    long v = s;
 // At least one of the two values generated here will be nonzero.
-this.x0 = RandomSupport.mixStafford13(s += RandomSupport.GOLDEN_RATIO_64);
+this.x0 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64);
-this.x1 = RandomSupport.mixStafford13(s + RandomSupport.GOLDEN_RATIO_64);
+this.x1 = RandomSupport.mixStafford13(v + RandomSupport.GOLDEN_RATIO_64);
 }
 }
 /**
 * Creates a new instance of {@link L64X128MixRandom} using the
 //
 // 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.
+// GOLDEN_RATIO_64 as the gamma value and mixStafford13 as the mixer.
 this(RandomSupport.mixMurmur64(seed ^= RandomSupport.SILVER_RATIO_64),
 1,
 RandomSupport.mixStafford13(seed),
 RandomSupport.mixStafford13(seed + RandomSupport.GOLDEN_RATIO_64));
 }
 }
 /* ---------------- public methods ---------------- */
 /**
-* Constructs and returns a new instance of {@link L64X128MixRandom}
+* Given 63 bits of "brine", constructs and returns a new instance of
-* that shares no mutable state with this instance.
+* {@code 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 {@link L64X128MixRandom} object.  Either or both of the two
+* a single {@code 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 {@link SplittableGenerator} instance to be used instead
+* @param source a {@code SplittableGenerator} instance to be used instead
 *               of this one as a source of pseudorandom bits used to
 *               initialize the state of the new ones.
-*
+* @param brine a long value, of which the low 63 bits are used to choose
-* @return a new instance of {@link L64X128MixRandom}
+*              the {@code a} parameter for the new instance.
-*/
+* @return a new instance of {@code L64X128MixRandom}
-public L64X128MixRandom split(SplittableGenerator source) {
+*/
-// Literally pick a new instance "at random".
+public SplittableGenerator split(SplittableGenerator source, long brine) {
-return new L64X128MixRandom(source.nextLong(), source.nextLong(),
+	// Pick a new instance "at random", but use the brine for `a`.
-source.nextLong(), source.nextLong());
+return new L64X128MixRandom(brine << 1, source.nextLong(),
+				    source.nextLong(), source.nextLong());
 }
 /**
 * Returns a pseudorandom {@code long} value.
 *
 * @return a pseudorandom {@code long} value
 */
 public long nextLong() {
-final long z = s + x0;
+	// Compute the result based on current state information
-s = M * s + a;  // LCG
+	// (this allows the computation to be overlapped with state update).
+final long result = RandomSupport.mixLea64(s + x0);
+	// Update the LCG subgenerator
+s = M * s + a;
+	// Update the Xorshift subgenerator
 long q0 = x0, q1 = x1;
 {   // xoroshiro128v1_0
 q1 ^= q0;
 q0 = Long.rotateLeft(q0, 24);
 q0 = q0 ^ q1 ^ (q1 << 16);
 q1 = Long.rotateLeft(q1, 37);
 }
 x0 = q0; x1 = q1;
-return Long.rotateLeft(z * 5, 7) * 9;  // "starstar" mixing function
+return result;
 }
+/**
+* Returns the period of this random generator.
+*
+* @return a {@link BigInteger} whose value is the number of distinct possible states of this
+*         {@link RandomGenerator} object (2<sup>64</sup>(2<sup>128</sup>-1)).
+*/
 public BigInteger period() {
 return PERIOD;
 }
 }

branch	JDK-8193209-branch
changeset 59080	1b314be4feb2
parent 57684	7cb325557832