Series of generated values pass the TestU01 BigCrush and PractRand test suites + *
+ * Series of generated values pass the TestU01 BigCrush and PractRand test suites * that measure independence and uniformity properties of random number generators. - * - *
The class {@code Xoroshiro128StarStar} uses the {@code xoroshiro128} algorithm, + *
+ * The class {@link Xoroshiro128StarStar} uses the {@code xoroshiro128} algorithm, * version 1.0 (parameters 24, 16, 37), with the "**" scrambler (a mixing function). * 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 generator is 2128-1. - * - *
The 64-bit values produced by the {@code nextLong()} method are equidistributed. + *
+ * The 64-bit values produced by the {@code nextLong()} method are equidistributed. * To be precise, over the course of the cycle of length 2128-1, * each nonzero {@code long} value is generated 264 times, * but the value 0 is generated only 264-1 times. * The values produced by the {@code nextInt()}, {@code nextFloat()}, and {@code nextDouble()} * methods are likewise equidistributed. - * - *
In fact, the 64-bit values produced by the {@code nextLong()} method are 2-equidistributed. + *
+ * In fact, the 64-bit values produced by the {@code nextLong()} method are 2-equidistributed. * To be precise: 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 2128-1 such subsequences, and each subsequence, @@ -64,25 +65,23 @@ * methods are likewise 2-equidistributed, but note that that the subsequence (0, 0) * can also appear (but occurring somewhat less frequently than all other subsequences), * because the values produced by those methods have fewer than 64 randomly chosen bits. - * - *
Instances {@code Xoroshiro128StarStar} are not thread-safe. + *
+ * Instances {@link Xoroshiro128StarStar} are not thread-safe. * They are designed to be used so that each thread as its own instance. * The methods {@link #jump} and {@link #leap} and {@link #jumps} and {@link #leaps} - * can be used to construct new instances of {@code Xoroshiro128StarStar} that traverse + * can be used to construct new instances of {@link Xoroshiro128StarStar} that traverse * other parts of the state cycle. - * - *
Instances of {@code Xoroshiro128StarStar} are not cryptographically + *
+ * Instances of {@link Xoroshiro128StarStar} 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
- * @author Doug Lea
- * @since 1.8
+ * @since 14
*/
-public final class Xoroshiro128StarStar implements LeapableRng {
+public final class Xoroshiro128StarStar implements LeapableRNG {
/*
* Implementation Overview.
@@ -115,7 +114,7 @@
*
* File organization: First the non-public methods that constitute the
* main algorithm, then the public methods. Note that many methods are
- * defined by classes {@code AbstractJumpableRng} and {@code AbstractRng}.
+ * defined by classes {@link AbstractJumpableRNG} and {@link AbstractRNG}.
*/
/* ---------------- static fields ---------------- */
@@ -123,13 +122,13 @@
/**
* The seed generator for default constructors.
*/
- private static final AtomicLong defaultGen = new AtomicLong(RngSupport.initialSeed());
+ private static final AtomicLong DEFAULT_GEN = new AtomicLong(RNGSupport.initialSeed());
/*
* The period of this generator, which is 2**128 - 1.
*/
- private static final BigInteger thePeriod =
- BigInteger.ONE.shiftLeft(128).subtract(BigInteger.ONE);
+ private static final BigInteger PERIOD =
+ BigInteger.ONE.shiftLeft(128).subtract(BigInteger.ONE);
/* ---------------- instance fields ---------------- */
@@ -150,92 +149,91 @@
* @param x1 second word of the initial state
*/
public Xoroshiro128StarStar(long x0, long x1) {
- 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(x0 += RngSupport.GOLDEN_RATIO_64);
- this.x1 = (x0 += RngSupport.GOLDEN_RATIO_64);
- }
+ // At least one of the two values generated here will be nonzero.
+ this.x0 = RNGSupport.mixStafford13(x0 += RNGSupport.GOLDEN_RATIO_64);
+ this.x1 = (x0 += RNGSupport.GOLDEN_RATIO_64);
+ }
}
/**
- * Creates a new instance of {@code Xoroshiro128StarStar} using the
+ * Creates a new instance of {@link Xoroshiro128StarStar} using the
* specified {@code long} value as the initial seed. Instances of
- * {@code Xoroshiro128StarStar} created with the same seed in the same
+ * {@link Xoroshiro128StarStar} created with the same seed in the same
* program generate identical sequences of values.
*
* @param seed the initial seed
*/
public Xoroshiro128StarStar(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 x values are then filled in as if by a SplitMix PRNG with
- // GOLDEN_RATIO_64 as the gamma value and Stafford13 as the mixer.
- this(RngSupport.mixStafford13(seed ^= RngSupport.SILVER_RATIO_64),
- 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 x values are then filled in as if by a SplitMix PRNG with
+ // GOLDEN_RATIO_64 as the gamma value and Stafford13 as the mixer.
+ this(RNGSupport.mixStafford13(seed ^= RNGSupport.SILVER_RATIO_64),
+ RNGSupport.mixStafford13(seed + RNGSupport.GOLDEN_RATIO_64));
}
/**
- * Creates a new instance of {@code Xoroshiro128StarStar} that is likely to
+ * Creates a new instance of {@link Xoroshiro128StarStar} 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 Xoroshiro128StarStar() {
- // 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(DEFAULT_GEN.getAndAdd(RNGSupport.GOLDEN_RATIO_64));
}
/**
- * Creates a new instance of {@code Xoroshiro128StarStar} using the specified array of
- * initial seed bytes. Instances of {@code Xoroshiro128StarStar} created with the same
+ * Creates a new instance of {@link Xoroshiro128StarStar} using the specified array of
+ * initial seed bytes. Instances of {@link Xoroshiro128StarStar} created with the same
* seed array in the same program execution generate identical sequences of values.
*
* @param seed the initial seed
*/
public Xoroshiro128StarStar(byte[] seed) {
- // Convert the seed to 2 long values, which are not both zero.
- long[] data = RngSupport.convertSeedBytesToLongs(seed, 2, 2);
- long x0 = data[0], x1 = data[1];
+ // Convert the seed to 2 long values, which are not both zero.
+ long[] data = RNGSupport.convertSeedBytesToLongs(seed, 2, 2);
+ long x0 = data[0], x1 = data[1];
this.x0 = x0;
this.x1 = x1;
}
-
+
/* ---------------- public methods ---------------- */
public Xoroshiro128StarStar copy() { return new Xoroshiro128StarStar(x0, x1); }
-/*
-
-To the extent possible under law, the author has dedicated all copyright
-and related and neighboring rights to this software to the public domain
-worldwide. This software is distributed without any warranty.
-
-See
+ * See
+ * Beside passing BigCrush, this generator passes the PractRand test suite up to (and included) + * 16TB, with the exception of binary rank tests, which fail due to the lowest bit being an + * LFSR; all other bits pass all tests. We suggest to use a sign test to extract a random + * Boolean value. + *
+ * Note that the generator uses a simulated rotate operation, which most C compilers will turn + * into a single instruction. In Java, you can use Long.rotateLeft(). In languages that do not + * make low-level rotation instructions accessible xorshift128+ could be faster. + *
+ * The state must be seeded so that it is not everywhere zero. If you have a 64-bit seed, we + * suggest to seed a splitmix64 generator and use its output to fill s. + */ /** * Returns a pseudorandom {@code long} value. @@ -243,52 +241,62 @@ * @return a pseudorandom {@code long} value */ public long nextLong() { - final long s0 = x0; - long s1 = x1; - final long z = s0; + final long s0 = x0; + long s1 = x1; + final long z = s0; - s1 ^= s0; - x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b - x1 = Long.rotateLeft(s1, 37); // c - - return Long.rotateLeft(z * 5, 7) * 9; // "starstar" mixing function + s1 ^= s0; + x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b + x1 = Long.rotateLeft(s1, 37); // c + + return Long.rotateLeft(z * 5, 7) * 9; // "starstar" mixing function } - public BigInteger period() { return thePeriod; } + public BigInteger period() { + return PERIOD; + } - public double defaultJumpDistance() { return 0x1.0p64; } + public double defaultJumpDistance() { + return 0x1.0p64; + } - public double defaultLeapDistance() { return 0x1.0p96; } + public double defaultLeapDistance() { + return 0x1.0p96; + } private static final long[] JUMP_TABLE = { 0xdf900294d8f554a5L, 0x170865df4b3201fcL }; - + private static final long[] LEAP_TABLE = { 0xd2a98b26625eee7bL, 0xdddf9b1090aa7ac1L }; - -/* This is the jump function for the generator. It is equivalent - to 2**64 calls to nextLong(); it can be used to generate 2**64 - non-overlapping subsequences for parallel computations. */ - public void jump() { jumpAlgorithm(JUMP_TABLE); } - -/* This is the long-jump function for the generator. It is equivalent to - 2**96 calls to next(); it can be used to generate 2**32 starting points, - from each of which jump() will generate 2**32 non-overlapping - subsequences for parallel distributed computations. */ + /** + * This is the jump function for the generator. It is equivalent to 2**64 calls to nextLong(); + * it can be used to generate 2**64 non-overlapping subsequences for parallel computations. + */ + public void jump() { + jumpAlgorithm(JUMP_TABLE); + } - public void leap() { jumpAlgorithm(LEAP_TABLE); } + /** + * This is the long-jump function for the generator. It is equivalent to 2**96 calls to next(); + * it can be used to generate 2**32 starting points, from each of which jump() will generate + * 2**32 non-overlapping subsequences for parallel distributed computations. + */ + public void leap() { + jumpAlgorithm(LEAP_TABLE); + } private void jumpAlgorithm(long[] table) { - long s0 = 0, s1 = 0; - for (int i = 0; i < table.length; i++) { - for (int b = 0; b < 64; b++) { - if ((table[i] & (1L << b)) != 0) { - s0 ^= x0; - s1 ^= x1; - } - nextLong(); - } - x0 = s0; - x1 = s1; - } + long s0 = 0, s1 = 0; + for (int i = 0; i < table.length; i++) { + for (int b = 0; b < 64; b++) { + if ((table[i] & (1L << b)) != 0) { + s0 ^= x0; + s1 ^= x1; + } + nextLong(); + } + x0 = s0; + x1 = s1; + } } }