jdk-sandbox: comparison src/java.base/share/classes/java/util/random/L64X1024MixRandom.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 L64X1024MixRandom} implements
 * least approximately, for others as well.
 * <p>
 * {@link L64X1024MixRandom} 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 L64X1024MixRandom} 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 L64X1024MixRandom} 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 L64X1024MixRandom}) and the addend
 * algorithm (parameters 25, 27, and 36), without any final scrambler such as "+" or "**".
 * Its state consists of an array {@code x} of sixteen {@code long} values,
 * which can take on any values provided that they are not all zero.
 * The period of this subgenerator is 2<sup>1024</sup>-1.
 * <p>
-* The mixing function for {@link L64X256MixRandom} is the 64-bit MurmurHash3 finalizer.
+* The mixing function for {@link L64X1024MixRandom} is {@link RandomSupport.mixLea64}
+* applied to the argument {@code (s + s0)}, where {@code s0} is the most recently computed
+* element of {@code x}.
 * <p>
 * Because the periods 2<sup>64</sup> and 2<sup>1024</sup>-1 of the two subgenerators
 * are relatively prime, the <em>period</em> of any single {@link L64X1024MixRandom} 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>1024</sup>-1),
 * There are 2<sup>64</sup>(2<sup>1024</sup>-1) such subsequences, and each subsequence,
 * which consists of 16 64-bit values, can have one of 2<sup>1024</sup> values. Of those
 * 2<sup>1024</sup> subsequence values, nearly all of them (2<sup>1024</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 L64X1024MixRandom} 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 16-equidistributed.
 * <p>
 * seed unless the {@linkplain System#getProperty system property}
 * {@code java.util.secureRandomSeed} is set to {@code true}.
 *
 * @since 14
 */
-public final class L64X1024MixRandom extends AbstractSplittableGenerator {
+public final class L64X1024MixRandom extends AbstractSplittableWithBrineGenerator {
 /*
 * Implementation Overview.
 *
 * The split() operation uses the current generator to choose 18 new 64-bit
 */
 private static final BigInteger PERIOD =
 BigInteger.ONE.shiftLeft(N*64).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.x[13] = x13;
 this.x[14] = x14;
 this.x[15] = x15;
 // If x0, x1, ..., x15 are all zero (very unlikely), we must choose nonzero values.
 if ((x0 | x1 | x2 | x3 | x4 | x5 | x6 | x7 | x8 | x9 | x10 | x11 | x12 | x13 | x14 | x15) == 0) {
+	    long v = s;
 // At least fifteen of the sixteen values generated here will be nonzero.
 for (int j = 0; j < N; j++) {
-this.x[j] = RandomSupport.mixStafford13(s += RandomSupport.GOLDEN_RATIO_64);
+this.x[j] = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64);
 }
 }
 }
 /**
 //
 // The seed is hashed by mixMurmur64 to produce the `a` parameter.
 // The seed is hashed by mixStafford13 to produce the initial `x[0]`,
 // which will then be used to produce the first generated value.
 // The other x values are 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),
 RandomSupport.mixStafford13(seed += RandomSupport.GOLDEN_RATIO_64),
 this.x[j] = data[2+j];
 }
 }
 /* ---------------- public methods ---------------- */
+/**
-/**
+* Given 63 bits of "brine", constructs and returns a new instance of
-* Constructs and returns a new instance of {@link L64X1024MixRandom}
+* {@code L64X1024MixRandom} that shares no mutable state with this instance.
-* 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 L64X1024MixRandom} object.  Either or both of the two
+* a single {@code L64X1024MixRandom} 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.
-* @return a new instance of {@link L64X1024MixRandom}
+* @param brine a long value, of which the low 63 bits are used to choose
-*/
+*              the {@code a} parameter for the new instance.
-public L64X1024MixRandom split(SplittableGenerator source) {
+* @return a new instance of {@code L64X1024MixRandom}
-// Literally pick a new instance "at random".
+*/
-return new L64X1024MixRandom(source.nextLong(), source.nextLong(),
+public SplittableGenerator split(SplittableGenerator source, long brine) {
-source.nextLong(), source.nextLong(),
+	// Pick a new instance "at random", but use the brine for `a`.
+return new L64X1024MixRandom(brine << 1, source.nextLong(),
+				     source.nextLong(), source.nextLong(),
 source.nextLong(), source.nextLong(),
 source.nextLong(), source.nextLong(),
 source.nextLong(), source.nextLong(),
 source.nextLong(), source.nextLong(),
 source.nextLong(), source.nextLong(),
 // First part of xoroshiro1024: fetch array data
 final int q = p;
 final long s0 = x[p = (p + 1) & (N - 1)];
 long s15 = x[q];
-final long z = s + s0;
+	// Compute the result based on current state information
+	// (this allows the computation to be overlapped with state update).
+	final long result = RandomSupport.mixLea64(s + s0);
+	// Update the LCG subgenerator
 s = M * s + a;  // LCG
 // Second part of xoroshiro1024: update array data
 s15 ^= s0;
 x[q] = Long.rotateLeft(s0, 25) ^ s15 ^ (s15 << 27);
 x[p] = Long.rotateLeft(s15, 36);
-return RandomSupport.mixLea64(z);  // 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>1024</sup>-1)).
+*/
 public BigInteger period() {
 return PERIOD;
 }
 }

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