--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/random/L128X256MixRandom.java.rej Thu Nov 14 12:50:08 2019 -0400
@@ -0,0 +1,353 @@
+***************
+*** 28,34 ****
+ import java.math.BigInteger;
+ import java.util.concurrent.atomic.AtomicLong;
+ import java.util.random.RandomGenerator.SplittableGenerator;
+- import java.util.random.RandomSupport.AbstractSplittableGenerator;
+
+
+ /**
+--- 28,34 ----
+ import java.math.BigInteger;
+ import java.util.concurrent.atomic.AtomicLong;
+ import java.util.random.RandomGenerator.SplittableGenerator;
++ import java.util.random.RandomSupport.AbstractSplittableWithBrineGenerator;
+
+
+ /**
+***************
+*** 55,63 ****
+ * {@link L128X256MixRandom} 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 {@link L128X256MixRandom} does use a mixing function).
+ * <p>
+ * The LCG subgenerator for {@link L128X256MixRandom} has an update step of the
+ * form {@code s = m * s + a}, where {@code s}, {@code m}, and {@code a} are all
+--- 55,64 ----
+ * {@link L128X256MixRandom} 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 result of
++ * combining state from the LCG with state from the Xorshift generator by
++ * 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 L128X256MixRandom} has an update step of the
+ * form {@code s = m * s + a}, where {@code s}, {@code m}, and {@code a} are all
+***************
+*** 74,80 ****
+ * and {@code x3}, which can take on any values provided that they are not all zero.
+ * The period of this subgenerator is 2<sup>256</sup>-1.
+ * <p>
+- * The mixing function for {@link L128X256MixRandom} is the 64-bit MurmurHash3 finalizer.
+ * <p>
+ * Because the periods 2<sup>128</sup> and 2<sup>256</sup>-1 of the two subgenerators
+ * are relatively prime, the <em>period</em> of any single {@link L128X256MixRandom} object
+--- 75,82 ----
+ * and {@code x3}, which can take on any values provided that they are not all zero.
+ * The period of this subgenerator is 2<sup>256</sup>-1.
+ * <p>
++ * The mixing function for {@link L128X256MixRandom} is {@link RandomSupport.mixLea64}
++ * applied to the argument {@code (sh + x0)}, where {@code sh} is the high half of {@code s}.
+ * <p>
+ * Because the periods 2<sup>128</sup> and 2<sup>256</sup>-1 of the two subgenerators
+ * are relatively prime, the <em>period</em> of any single {@link L128X256MixRandom} object
+***************
+*** 86,119 ****
+ * <p>
+ * The 64-bit values produced by the {@code nextLong()} method are exactly equidistributed.
+ * For any specific instance of {@link L128X256MixRandom}, over the course of its cycle each
+- * of the 2<sup>64</sup> possible {@code long} values will be produced 2<sup>256</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 exactly
+- * 2-equidistributed. For any specific instance of {@link L128X256MixRandom}, 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>128</sup>(2<sup>256</sup>-1) such subsequences, and each subsequence,
+- * which consists of 2 64-bit values, can have one of 2<sup>128</sup> values, and each
+- * such value occurs 2<sup>256</sup>-1 times. The values produced by the {@code nextInt()},
+- * {@code nextFloat()}, and {@code nextDouble()} methods are likewise exactly 2-equidistributed.
+ * <p>
+- * Moreover, the 64-bit values produced by the {@code nextLong()} method are 4-equidistributed.
+- * To be precise: for any specific instance of {@link L128X256MixRandom}, consider
+- * the (overlapping) length-4 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 <sup>128</sup>(2<sup>256</sup>-1) such subsequences, and each subsequence,
+- * which consists of 4 64-bit values, can have one of 2<sup>256</sup> values. Of those
+- * 2<sup>256</sup> subsequence values, nearly all of them (2<sup>256</sup>-2<sup>128</sup>)
+- * occur 2<sup>128</sup> times over the course of the entire cycle, and the other
+- * 2<sup>128</sup> subsequence values occur only 2<sup>128</sup>-1 times. So the ratio
+- * 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>-128</sup>.
+- * (Note that the set of 2<sup>128</sup> less-common subsequence values will differ from
+- * one instance of {@link L128X256MixRandom} 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 4-equidistributed.
+ * <p>
+ * Method {@link #split} constructs and returns a new {@link L128X256MixRandom}
+ * instance that shares no mutable state with the current instance. However, with
+--- 88,103 ----
+ * <p>
+ * The 64-bit values produced by the {@code nextLong()} method are exactly equidistributed.
+ * For any specific instance of {@link L128X256MixRandom}, over the course of its cycle each
++ * of the 2<sup>64</sup> possible {@code long} values will be produced
++ * 2<sup>64</sup>(2<sup>256</sup>-1) times. The values produced by the {@code nextInt()},
++ * {@code nextFloat()}, and {@code nextDouble()} methods are likewise exactly equidistributed.
+ * <p>
++ * Moreover, 64-bit values produced by the {@code nextLong()} method are conjectured to be
++ * "very nearly" 4-equidistributed: all possible quadruples of 64-bit values are generated,
++ * and some pairs occur more often than others, but only very slightly more often.
++ * However, this conjecture has not yet been proven mathematically.
++ * If this conjecture is true, then the values produced by the {@code nextInt()}, {@code nextFloat()},
++ * and {@code nextDouble()} methods are likewise approximately 4-equidistributed.
+ * <p>
+ * Method {@link #split} constructs and returns a new {@link L128X256MixRandom}
+ * instance that shares no mutable state with the current instance. However, with
+***************
+*** 146,152 ****
+ *
+ * @since 14
+ */
+- public final class L128X256MixRandom extends AbstractSplittableGenerator {
+
+ /*
+ * Implementation Overview.
+--- 130,136 ----
+ *
+ * @since 14
+ */
++ public final class L128X256MixRandom extends AbstractSplittableWithBrineGenerator {
+
+ /*
+ * Implementation Overview.
+***************
+*** 193,220 ****
+ BigInteger.ONE.shiftLeft(256).subtract(BigInteger.ONE).shiftLeft(128);
+
+ /*
+- * The multiplier used in the LCG portion of the algorithm is 2**64 + m;
+- * where m is taken from
+- * Pierre L'Ecuyer, Tables of linear congruential generators of
+- * different sizes and good lattice structure, <em>Mathematics of
+- * Computation</em> 68, 225 (January 1999), pages 249-260,
+- * Table 4 (first multiplier for size 2<sup>64</sup>).
+- *
+- * This is almost certainly not the best possible 128-bit multiplier
+- * for an LCG, but it is sufficient for our purposes here; because
+- * is is larger than 2**64, the 64-bit values produced by nextLong()
+- * are exactly 2-equidistributed, and the fact that it is of the
+- * form (2**64 + m) simplifies the code, given that we have only
+- * 64-bit arithmetic to work with.
+ */
+
+- private static final long M = 2862933555777941757L;
+
+ /* ---------------- instance fields ---------------- */
+
+ /**
+ * The parameter that is used as an additive constant for the LCG.
+- * Must be odd.
+ */
+ private final long ah, al;
+
+--- 177,196 ----
+ BigInteger.ONE.shiftLeft(256).subtract(BigInteger.ONE).shiftLeft(128);
+
+ /*
++ * Low half of multiplier used in the LCG portion of the algorithm;
++ * the overall multiplier is (2**64 + ML).
++ * Chosen based on research by Sebastiano Vigna and Guy Steele (2019).
++ * The spectral scores for dimensions 2 through 8 for the multiplier 0x1d605bbb58c8abbfdLL
++ * are [0.991889, 0.907938, 0.830964, 0.837980, 0.780378, 0.797464, 0.761493].
+ */
+
++ private static final long ML = 0xd605bbb58c8abbfdL;
+
+ /* ---------------- instance fields ---------------- */
+
+ /**
+ * The parameter that is used as an additive constant for the LCG.
++ * Must be odd (therefore al must be odd).
+ */
+ private final long ah, al;
+
+***************
+*** 252,262 ****
+ this.x3 = x3;
+ // If x0, x1, x2, and x3 are all zero, we must choose nonzero values.
+ if ((x0 | x1 | x2 | x3) == 0) {
+ // At least three of the four values generated here will be nonzero.
+- this.x0 = RandomSupport.mixStafford13(sh += RandomSupport.GOLDEN_RATIO_64);
+- this.x1 = RandomSupport.mixStafford13(sh += RandomSupport.GOLDEN_RATIO_64);
+- this.x2 = RandomSupport.mixStafford13(sh += RandomSupport.GOLDEN_RATIO_64);
+- this.x3 = RandomSupport.mixStafford13(sh + RandomSupport.GOLDEN_RATIO_64);
+ }
+ }
+
+--- 228,239 ----
+ this.x3 = x3;
+ // If x0, x1, x2, and x3 are all zero, we must choose nonzero values.
+ if ((x0 | x1 | x2 | x3) == 0) {
++ long v = sh;
+ // At least three of the four values generated here will be nonzero.
++ this.x0 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64);
++ this.x1 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64);
++ this.x2 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64);
++ this.x3 = RandomSupport.mixStafford13(v + RandomSupport.GOLDEN_RATIO_64);
+ }
+ }
+
+***************
+*** 277,283 ****
+ // The seed is hashed by mixStafford13 to produce the initial `x0`,
+ // 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.
+ this(RandomSupport.mixMurmur64(seed ^= RandomSupport.SILVER_RATIO_64),
+ RandomSupport.mixMurmur64(seed += RandomSupport.GOLDEN_RATIO_64),
+ 0,
+--- 254,260 ----
+ // The seed is hashed by mixStafford13 to produce the initial `x0`,
+ // 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 mixStafford13 as the mixer.
+ this(RandomSupport.mixMurmur64(seed ^= RandomSupport.SILVER_RATIO_64),
+ RandomSupport.mixMurmur64(seed += RandomSupport.GOLDEN_RATIO_64),
+ 0,
+***************
+*** 323,351 ****
+ }
+
+ /* ---------------- public methods ---------------- */
+-
+ /**
+- * Constructs and returns a new instance of {@link L128X256MixRandom}
+- * 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 L128X256MixRandom} 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
+ * of this one as a source of pseudorandom bits used to
+ * initialize the state of the new ones.
+- * @return a new instance of {@link L128X256MixRandom}
+ */
+- public L128X256MixRandom split(SplittableGenerator source) {
+- // Literally pick a new instance "at random".
+- return new L128X256MixRandom(source.nextLong(), source.nextLong(),
+- source.nextLong(), source.nextLong(),
+- source.nextLong(), source.nextLong(),
+- source.nextLong(), source.nextLong());
+ }
+
+ /**
+--- 300,330 ----
+ }
+
+ /* ---------------- public methods ---------------- */
++
+ /**
++ * Given 63 bits of "brine", constructs and returns a new instance of
++ * {@code L128X256MixRandom} 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 L128X256MixRandom} 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 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
++ * the {@code a} parameter for the new instance.
++ * @return a new instance of {@code L128X256MixRandom}
+ */
++ public SplittableGenerator split(SplittableGenerator source, long brine) {
++ // Pick a new instance "at random", but use the brine for (the low half of) `a`.
++ return new L128X256MixRandom(source.nextLong(), brine << 1,
++ source.nextLong(), source.nextLong(),
++ source.nextLong(), source.nextLong(),
++ source.nextLong(), source.nextLong());
+ }
+
+ /**
+***************
+*** 354,365 ****
+ * @return a pseudorandom {@code long} value
+ */
+ public long nextLong() {
+- final long z = sh + x0;
+- // The LCG: in effect, s = ((1LL << 64) + M) * s + a, if only we had 128-bit arithmetic.
+- final long u = M * sl;
+- sh = (M * sh) + Math.multiplyHigh(M, sl) + sl + ah;
+ sl = u + al;
+ if (Long.compareUnsigned(sl, u) < 0) ++sh; // Handle the carry propagation from low half to high half.
+ long q0 = x0, q1 = x1, q2 = x2, q3 = x3;
+ { // xoshiro256 1.0
+ long t = q1 << 17;
+--- 333,359 ----
+ * @return a pseudorandom {@code long} value
+ */
+ public long nextLong() {
++ // Compute the result based on current state information
++ // (this allows the computation to be overlapped with state update).
++ final long result = RandomSupport.mixLea64(sh + x0);
++
++ // Update the LCG subgenerator
++ // The LCG is, in effect, s = ((1LL << 64) + ML) * s + a, if only we had 128-bit arithmetic.
++ final long u = ML * sl;
++ // Note that Math.multiplyHigh computes the high half of the product of signed values,
++ // but what we need is the high half of the product of unsigned values; for this we use the
++ // formula "unsignedMultiplyHigh(a, b) = multiplyHigh(a, b) + ((a >> 63) & b) + ((b >> 63) & a)";
++ // in effect, each operand is added to the result iff the sign bit of the other operand is 1.
++ // (See Henry S. Warren, Jr., _Hacker's Delight_ (Second Edition), Addison-Wesley (2013),
++ // Section 8-3, p. 175; or see the First Edition, Addison-Wesley (2003), Section 8-3, p. 133.)
++ // If Math.unsignedMultiplyHigh(long, long) is ever implemented, the following line can become:
++ // sh = (ML * sh) + Math.unsignedMultiplyHigh(ML, sl) + sl + ah;
++ // and this entire comment can be deleted.
++ sh = (ML * sh) + (Math.multiplyHigh(ML, sl) + ((ML >> 63) & sl) + ((sl >> 63) & ML)) + sl + ah;
+ sl = u + al;
+ if (Long.compareUnsigned(sl, u) < 0) ++sh; // Handle the carry propagation from low half to high half.
++
++ // Update the Xorshift subgenerator
+ long q0 = x0, q1 = x1, q2 = x2, q3 = x3;
+ { // xoshiro256 1.0
+ long t = q1 << 17;
+***************
+*** 371,379 ****
+ q3 = Long.rotateLeft(q3, 45);
+ }
+ x0 = q0; x1 = q1; x2 = q2; x3 = q3;
+- return RandomSupport.mixLea64(z); // mixing function
+ }
+
+ public BigInteger period() {
+ return PERIOD;
+ }
+--- 365,379 ----
+ q3 = Long.rotateLeft(q3, 45);
+ }
+ x0 = q0; x1 = q1; x2 = q2; x3 = q3;
++ 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>128</sup>(2<sup>256</sup>-1)).
++ */
+ public BigInteger period() {
+ return PERIOD;
+ }