1 /*

     2  * Copyright (c) 2013, 2019, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package java.util.random;

    27 

    28 import java.math.BigInteger;

    29 import java.util.concurrent.atomic.AtomicLong;

    30 import java.util.random.RandomGenerator.LeapableGenerator;

    31 import java.util.random.RandomSupport.AbstractArbitrarilyJumpableGenerator;

    32 

    33 /**

    34  * A generator of uniform pseudorandom values applicable for use in

    35  * (among other contexts) isolated parallel computations that may

    36  * generate subtasks.  Class {@link MRG32k3a} implements

    37  * interfaces {@link RandomGenerator} and {@link AbstractArbitrarilyJumpableGenerator},

    38  * and therefore supports methods for producing pseudorandomly chosen

    39  * numbers of type {@code int}, {@code long}, {@code float}, and {@code double}

    40  * as well as creating new {@link Xoroshiro128PlusMRG32k3a} objects

    41  * by "jumping" or "leaping".

    42  * <p>

    43  * Instances {@link Xoroshiro128Plus} are <em>not</em> thread-safe.

    44  * They are designed to be used so that each thread as its own instance.

    45  * The methods {@link #jump} and {@link #leap} and {@link #jumps} and {@link #leaps}

    46  * can be used to construct new instances of {@link Xoroshiro128Plus} that traverse

    47  * other parts of the state cycle.

    48  * <p>

    49  * Instances of {@link MRG32k3a} are not cryptographically

    50  * secure.  Consider instead using {@link java.security.SecureRandom}

    51  * in security-sensitive applications. Additionally,

    52  * default-constructed instances do not use a cryptographically random

    53  * seed unless the {@linkplain System#getProperty system property}

    54  * {@code java.util.secureRandomSeed} is set to {@code true}.

    55  *

    56  * @since 14

    57  */

    58 public final class MRG32k3a extends AbstractArbitrarilyJumpableGenerator {

    59 

    60     /*

    61      * Implementation Overview.

    62      *

    63      * See http://simul.iro.umontreal.ca/rng/MRG32k3a.c .

    64      *

    65      * File organization: First the non-public methods that constitute

    66      * the main algorithm, then the main public methods, followed by

    67      * some custom spliterator classes needed for stream methods.

    68      */

    69 

    70     private final static double NORM1 = 2.328306549295728e-10;

    71     private final static double NORM2 = 2.328318824698632e-10;

    72     private final static double M1 =   4294967087.0;

    73     private final static double M2 =   4294944443.0;

    74     private final static double A12 =     1403580.0;

    75     private final static double A13N =     810728.0;

    76     private final static double A21 =      527612.0;

    77     private final static double A23N =    1370589.0;

    78     private final static int M1_DEFICIT = 209;

    79 

    80     /**

    81      * The per-instance state.

    82      The seeds for s10, s11, s12 must be integers in [0, m1 - 1] and not all 0.

    83      The seeds for s20, s21, s22 must be integers in [0, m2 - 1] and not all 0.

    84      */

    85     private double s10, s11, s12,

    86                    s20, s21, s22;

    87 

    88     /**

    89      * The seed generator for default constructors.

    90      */

    91     private static final AtomicLong DEFAULT_GEN =

    92         new AtomicLong(RandomSupport.initialSeed());

    93 

    94     /*

    95       32-bits Random number generator U(0,1): MRG32k3a

    96       Author: Pierre L'Ecuyer,

    97       Source: Good Parameter Sets for Combined Multiple Recursive Random

    98            Number Generators,

    99            Shorter version in Operations Research,

   100            47, 1 (1999), 159--164.

   101            ---------------------------------------------------------

   102     */

   103 

   104     private void nextState() {

   105         /* Component 1 */

   106         double p1 = A12 * s11 - A13N * s10;

   107         double k1 = p1 / M1;   p1 -= k1 * M1;   if (p1 < 0.0) p1 += M1;

   108         s10 = s11;   s11 = s12;   s12 = p1;

   109         /* Component 2 */

   110         double p2 = A21 * s22 - A23N * s20;

   111         double k2 = p2 / M2;   p2 -= k2 * M2;   if (p2 < 0.0) p2 += M2;

   112         s20 = s21;   s21 = s22;   s22 = p2;

   113     }

   114 

   115 

   116     /**

   117      * The form of nextInt used by IntStream Spliterators.

   118      * Exactly the same as long version, except for types.

   119      *

   120      * @param origin the least value, unless greater than bound

   121      * @param bound the upper bound (exclusive), must not equal origin

   122      *

   123      * @return a pseudorandom value

   124      */

   125     private int internalNextInt(int origin, int bound) {

   126         if (origin < bound) {

   127             final int n = bound - origin;

   128             final int m = n - 1;

   129             if (n > 0) {

   130                 int r;

   131                 for (int u = (int)nextDouble() >>> 1;

   132                      u + m + ((M1_DEFICIT + 1) >>> 1) - (r = u % n) < 0;

   133                      u = (int)nextDouble() >>> 1)

   134                     ;

   135                 return (r + origin);

   136             } else {

   137                 return RandomSupport.boundedNextInt(this, origin, bound);

   138             }

   139         } else {

   140             return nextInt();

   141         }

   142     }

   143 

   144     private int internalNextInt(int bound) {

   145         // Specialize internalNextInt for origin == 0, bound > 0

   146         final int n = bound;

   147         final int m = n - 1;

   148         int r;

   149         for (int u = (int)nextDouble() >>> 1;

   150              u + m + ((M1_DEFICIT + 1) >>> 1) - (r = u % n) < 0;

   151              u = (int)nextDouble() >>> 1)

   152             ;

   153         return r;

   154     }

   155 

   156     /**

   157      * All arguments must be known to be nonnegative integral values

   158      * less than the appropriate modulus.

   159      */

   160     private MRG32k3a(double s10, double s11, double s12,

   161                      double s20, double s21, double s22) {

   162         this.s10 = s10; this.s11 = s11; this.s12 = s12;

   163         this.s20 = s20; this.s21 = s21; this.s22 = s22;

   164         if ((s10 == 0.0) && (s11 == 0.0) && (s12 == 0.0)) {

   165             this.s10 = this.s11 = this.s12 = 12345.0;

   166         }

   167         if ((s20 == 0.0) && (s21 == 0.0) && (s22 == 0.0)) {

   168             this.s20 = this.s21 = this.s21 = 12345.0;

   169         }

   170     }

   171 

   172     /* ---------------- public methods ---------------- */

   173 

   174     /**

   175      * Creates a new MRG32k3a instance using six specified {@code int}

   176      * initial seed values. MRG32k3a instances created with the same

   177      * seeds in the same program generate identical sequences of values.

   178      * If all six seed values are zero, the generator is seeded to a

   179      * widely used initialization of MRG32k3a: all six state variables

   180      * are set to 12345.

   181      *

   182      * @param s10 the first seed value for the first subgenerator

   183      * @param s11 the second seed value for the first subgenerator

   184      * @param s12 the third seed value for the first subgenerator

   185      * @param s20 the first seed value for the second subgenerator

   186      * @param s21 the second seed value for the second subgenerator

   187      * @param s22 the third seed value for the second subgenerator

   188      */

   189     public MRG32k3a(int s10, int s11, int s12,

   190                     int s20, int s21, int s22) {

   191         this(((double)(((long)s10) & 0x00000000ffffffffL)) % M1,

   192              ((double)(((long)s11) & 0x00000000ffffffffL)) % M1,

   193              ((double)(((long)s12) & 0x00000000ffffffffL)) % M1,

   194              ((double)(((long)s20) & 0x00000000ffffffffL)) % M2,

   195              ((double)(((long)s21) & 0x00000000ffffffffL)) % M2,

   196              ((double)(((long)s22) & 0x00000000ffffffffL)) % M2);

   197     }

   198 

   199     /**

   200      * Creates a new MRG32k3a instance using the specified

   201      * initial seed. MRG32k3a instances created with the same

   202      * seed in the same program generate identical sequences of values.

   203      * An argument of 0 seeds the generator to a widely used initialization

   204      * of MRG32k3a: all six state variables are set to 12345.

   205      *

   206      * @param seed the initial seed

   207      */

   208     public MRG32k3a(long seed) {

   209         this((double)((seed & 0x7FF) + 12345),

   210              (double)(((seed >>> 11) & 0x7FF) + 12345),

   211              (double)(((seed >>> 22) & 0x7FF) + 12345),

   212              (double)(((seed >>> 33) & 0x7FF) + 12345),

   213              (double)(((seed >>> 44) & 0x7FF) + 12345),

   214              (double)((seed >>> 55) + 12345));

   215     }

   216 

   217     /**

   218      * Creates a new MRG32k3a instance that is likely to

   219      * generate sequences of values that are statistically independent

   220      * of those of any other instances in the current program; and

   221      * may, and typically does, vary across program invocations.

   222      */

   223     public MRG32k3a() {

   224         this(DEFAULT_GEN.getAndAdd(RandomSupport.GOLDEN_RATIO_64));

   225     }

   226 

   227     /**

   228      * Creates a new instance of {@link Xoshiro256StarStar} using the specified array of

   229      * initial seed bytes. Instances of {@link Xoshiro256StarStar} created with the same

   230      * seed array in the same program execution generate identical sequences of values.

   231      *

   232      * @param seed the initial seed

   233      */

   234     public MRG32k3a(byte[] seed) {

   235         // Convert the seed to 6 int values.

   236         int[] data = RandomSupport.convertSeedBytesToInts(seed, 6, 0);

   237         int s10 = data[0], s11 = data[1], s12 = data[2];

   238         int s20 = data[3], s21 = data[4], s22 = data[5];

   239         this.s10 = ((double)(((long)s10) & 0x00000000ffffffffL)) % M1;

   240         this.s11 = ((double)(((long)s11) & 0x00000000ffffffffL)) % M1;

   241         this.s12 = ((double)(((long)s12) & 0x00000000ffffffffL)) % M1;

   242         this.s20 = ((double)(((long)s20) & 0x00000000ffffffffL)) % M2;

   243         this.s21 = ((double)(((long)s21) & 0x00000000ffffffffL)) % M2;

   244         this.s22 = ((double)(((long)s22) & 0x00000000ffffffffL)) % M2;

   245         if ((s10 == 0.0) && (s11 == 0.0) && (s12 == 0.0)) {

   246             this.s10 = this.s11 = this.s12 = 12345.0;

   247         }

   248         if ((s20 == 0.0) && (s21 == 0.0) && (s22 == 0.0)) {

   249             this.s20 = this.s21 = this.s21 = 12345.0;

   250         }

   251     }

   252 

   253     public MRG32k3a copy() {

   254         return new MRG32k3a(s10, s11, s12, s20, s21, s22);

   255     }

   256 

   257     /**

   258      * Returns a pseudorandom {@code double} value between zero

   259      * (exclusive) and one (exclusive).

   260      *

   261      * @return a pseudorandom {@code double} value between zero

   262      *         (exclusive) and one (exclusive)

   263      */

   264     public double nextOpenDouble() {

   265         nextState();

   266         double p1 = s12, p2 = s22;

   267         if (p1 <= p2)

   268             return ((p1 - p2 + M1) * NORM1);

   269         else

   270             return ((p1 - p2) * NORM1);

   271     }

   272 

   273     /**

   274      * Returns a pseudorandom {@code double} value between zero

   275      * (inclusive) and one (exclusive).

   276      *

   277      * @return a pseudorandom {@code double} value between zero

   278      *         (inclusive) and one (exclusive)

   279      */

   280     public double nextDouble() {

   281         nextState();

   282         double p1 = s12, p2 = s22;

   283         final double p = p1 * NORM1 - p2 * NORM2;

   284         if (p < 0.0) return (p + 1.0);

   285         else return p;

   286     }

   287 

   288 

   289     /**

   290      * Returns a pseudorandom {@code float} value between zero

   291      * (inclusive) and one (exclusive).

   292      *

   293      * @return a pseudorandom {@code float} value between zero

   294      *         (inclusive) and one (exclusive)

   295      */

   296     public float nextFloat() {

   297         return (float)nextDouble();

   298     }

   299 

   300     /**

   301      * Returns a pseudorandom {@code int} value.

   302      *

   303      * @return a pseudorandom {@code int} value

   304      */

   305     public int nextInt() {

   306         return (internalNextInt(0x10000) << 16) | internalNextInt(0x10000);

   307     }

   308 

   309     /**

   310      * Returns a pseudorandom {@code long} value.

   311      *

   312      * @return a pseudorandom {@code long} value

   313      */

   314 

   315     public long nextLong() {

   316          return (((long)internalNextInt(0x200000) << 43) |

   317                 ((long)internalNextInt(0x200000) << 22) |

   318                 ((long)internalNextInt(0x400000)));

   319     }

   320 

   321     // Period is (m1**3 - 1)(m2**3 - 1)/2, or approximately 2**191.

   322     static BigInteger calculateThePeriod() {

   323         BigInteger bigm1 = BigInteger.valueOf((long)M1);

   324         BigInteger bigm2 = BigInteger.valueOf((long)M2);

   325         BigInteger t1 = bigm1.multiply(bigm1).multiply(bigm1).subtract(BigInteger.ONE);

   326         BigInteger t2 = bigm2.multiply(bigm2).multiply(bigm2).subtract(BigInteger.ONE);

   327         return t1.shiftRight(1).multiply(t2);

   328     }

   329 

   330     static final BigInteger PERIOD = calculateThePeriod();

   331 

   332     public BigInteger period() {

   333         return PERIOD;

   334     }

   335 

   336     // Jump and leap distances recommended in Section 1.3 of this paper:

   337     // Pierre L'Ecuyer, Richard Simard, E. Jack Chen, and W. David Kelton.

   338     // An Object-Oriented Random-Number Package with Many Long Streams and Substreams.

   339     // Operations Research 50, 6 (Nov--Dec 2002), 1073--1075.

   340 

   341     public double defaultJumpDistance() {

   342         return 0x1.0p76;   // 2**76

   343     }

   344 

   345     public double defaultLeapDistance() {

   346         return 0x1.0p127;   // 2**127

   347     }

   348 

   349     public void jump(double distance) {

   350         if (distance < 0.0 || Double.isInfinite(distance) || distance != Math.floor(distance))

   351             throw new IllegalArgumentException("jump distance must be a nonnegative finite integer");

   352             // We will compute a jump transformation (s => M s) for each LCG.

   353             // We initialize each transformation to the identity transformation.

   354             // Each will be turned into the d'th power of the corresponding base transformation.

   355         long m1_00 = 1, m1_01 = 0, m1_02 = 0,

   356              m1_10 = 0, m1_11 = 1, m1_12 = 0,

   357              m1_20 = 0, m1_21 = 0, m1_22 = 1;

   358         long m2_00 = 1, m2_01 = 0, m2_02 = 0,

   359              m2_10 = 0, m2_11 = 1, m2_12 = 0,

   360              m2_20 = 0, m2_21 = 0, m2_22 = 1;

   361         // These are the base transformations, which will be repeatedly squared,

   362         // and composed with the computed transformations for each 1-bit in distance.

   363         long t1_00 = 0,           t1_01 = 1,         t1_02 = 0,

   364              t1_10 = 0,           t1_11 = 0,         t1_12 = 1,

   365              t1_20 = -(long)A13N, t1_21 = (long)A12, t1_22 = 0;

   366         long t2_00 = 0,           t2_01 = 1,         t2_02 = 0,

   367              t2_10 = 0,           t2_11 = 0,         t2_12 = 1,

   368              t2_20 = -(long)A23N, t2_21 = (long)A21, t2_22 = 0;

   369         while (distance > 0.0) {

   370             final double dhalf = 0.5 * distance;

   371             if (Math.floor(dhalf) != dhalf) {

   372                 // distance is odd: accumulate current squaring

   373                 final long n1_00 = m1_00 * t1_00 + m1_01 * t1_10 + m1_02 * t1_20;

   374                 final long n1_01 = m1_00 * t1_01 + m1_01 * t1_11 + m1_02 * t1_21;

   375                 final long n1_02 = m1_00 * t1_02 + m1_01 * t1_12 + m1_02 * t1_22;

   376                 final long n1_10 = m1_10 * t1_00 + m1_11 * t1_10 + m1_12 * t1_20;

   377                 final long n1_11 = m1_10 * t1_01 + m1_11 * t1_11 + m1_12 * t1_21;

   378                 final long n1_12 = m1_10 * t1_02 + m1_11 * t1_12 + m1_12 * t1_22;

   379                 final long n1_20 = m1_20 * t1_00 + m1_21 * t1_10 + m1_22 * t1_20;

   380                 final long n1_21 = m1_20 * t1_01 + m1_21 * t1_11 + m1_22 * t1_21;

   381                 final long n1_22 = m1_20 * t1_02 + m1_21 * t1_12 + m1_22 * t1_22;

   382                 m1_00 = Math.floorMod(n1_00, (long)M1);

   383                 m1_01 = Math.floorMod(n1_01, (long)M1);

   384                 m1_02 = Math.floorMod(n1_02, (long)M1);

   385                 m1_10 = Math.floorMod(n1_10, (long)M1);

   386                 m1_11 = Math.floorMod(n1_11, (long)M1);

   387                 m1_12 = Math.floorMod(n1_12, (long)M1);

   388                 m1_20 = Math.floorMod(n1_20, (long)M1);

   389                 m1_21 = Math.floorMod(n1_21, (long)M1);

   390                 m1_22 = Math.floorMod(n1_22, (long)M1);

   391                 final long n2_00 = m2_00 * t2_00 + m2_01 * t2_10 + m2_02 * t2_20;

   392                 final long n2_01 = m2_00 * t2_01 + m2_01 * t2_11 + m2_02 * t2_21;

   393                 final long n2_02 = m2_00 * t2_02 + m2_01 * t2_12 + m2_02 * t2_22;

   394                 final long n2_10 = m2_10 * t2_00 + m2_11 * t2_10 + m2_12 * t2_20;

   395                 final long n2_11 = m2_10 * t2_01 + m2_11 * t2_11 + m2_12 * t2_21;

   396                 final long n2_12 = m2_10 * t2_02 + m2_11 * t2_12 + m2_12 * t2_22;

   397                 final long n2_20 = m2_20 * t2_00 + m2_21 * t2_10 + m2_22 * t2_20;

   398                 final long n2_21 = m2_20 * t2_01 + m2_21 * t2_11 + m2_22 * t2_21;

   399                 final long n2_22 = m2_20 * t2_02 + m2_21 * t2_12 + m2_22 * t2_22;

   400                 m2_00 = Math.floorMod(n2_00, (long)M2);

   401                 m2_01 = Math.floorMod(n2_01, (long)M2);

   402                 m2_02 = Math.floorMod(n2_02, (long)M2);

   403                 m2_10 = Math.floorMod(n2_10, (long)M2);

   404                 m2_11 = Math.floorMod(n2_11, (long)M2);

   405                 m2_12 = Math.floorMod(n2_12, (long)M2);

   406                 m2_20 = Math.floorMod(n2_20, (long)M2);

   407                 m2_21 = Math.floorMod(n2_21, (long)M2);

   408                 m2_22 = Math.floorMod(n2_22, (long)M2);

   409             }

   410             // Square the base transformations.

   411             {

   412                 final long z1_00 = m1_00 * m1_00 + m1_01 * m1_10 + m1_02 * m1_20;

   413                 final long z1_01 = m1_00 * m1_01 + m1_01 * m1_11 + m1_02 * m1_21;

   414                 final long z1_02 = m1_00 * m1_02 + m1_01 * m1_12 + m1_02 * m1_22;

   415                 final long z1_10 = m1_10 * m1_00 + m1_11 * m1_10 + m1_12 * m1_20;

   416                 final long z1_11 = m1_10 * m1_01 + m1_11 * m1_11 + m1_12 * m1_21;

   417                 final long z1_12 = m1_10 * m1_02 + m1_11 * m1_12 + m1_12 * m1_22;

   418                 final long z1_20 = m1_20 * m1_00 + m1_21 * m1_10 + m1_22 * m1_20;

   419                 final long z1_21 = m1_20 * m1_01 + m1_21 * m1_11 + m1_22 * m1_21;

   420                 final long z1_22 = m1_20 * m1_02 + m1_21 * m1_12 + m1_22 * m1_22;

   421                 m1_00 = Math.floorMod(z1_00, (long)M1);

   422                 m1_01 = Math.floorMod(z1_01, (long)M1);

   423                 m1_02 = Math.floorMod(z1_02, (long)M1);

   424                 m1_10 = Math.floorMod(z1_10, (long)M1);

   425                 m1_11 = Math.floorMod(z1_11, (long)M1);

   426                 m1_12 = Math.floorMod(z1_12, (long)M1);

   427                 m1_20 = Math.floorMod(z1_20, (long)M1);

   428                 m1_21 = Math.floorMod(z1_21, (long)M1);

   429                 m1_22 = Math.floorMod(z1_22, (long)M1);

   430                 final long z2_00 = m2_00 * m2_00 + m2_01 * m2_10 + m2_02 * m2_20;

   431                 final long z2_01 = m2_00 * m2_01 + m2_01 * m2_11 + m2_02 * m2_21;

   432                 final long z2_02 = m2_00 * m2_02 + m2_01 * m2_12 + m2_02 * m2_22;

   433                 final long z2_10 = m2_10 * m2_00 + m2_11 * m2_10 + m2_12 * m2_20;

   434                 final long z2_11 = m2_10 * m2_01 + m2_11 * m2_11 + m2_12 * m2_21;

   435                 final long z2_12 = m2_10 * m2_02 + m2_11 * m2_12 + m2_12 * m2_22;

   436                 final long z2_20 = m2_20 * m2_00 + m2_21 * m2_10 + m2_22 * m2_20;

   437                 final long z2_21 = m2_20 * m2_01 + m2_21 * m2_11 + m2_22 * m2_21;

   438                 final long z2_22 = m2_20 * m2_02 + m2_21 * m2_12 + m2_22 * m2_22;

   439                 m2_00 = Math.floorMod(z2_00, (long)M2);

   440                 m2_01 = Math.floorMod(z2_01, (long)M2);

   441                 m2_02 = Math.floorMod(z2_02, (long)M2);

   442                 m2_10 = Math.floorMod(z2_10, (long)M2);

   443                 m2_11 = Math.floorMod(z2_11, (long)M2);

   444                 m2_12 = Math.floorMod(z2_12, (long)M2);

   445                 m2_20 = Math.floorMod(z2_20, (long)M2);

   446                 m2_21 = Math.floorMod(z2_21, (long)M2);

   447                 m2_22 = Math.floorMod(z2_22, (long)M2);

   448             }

   449             // Divide distance by 2.

   450             distance = dhalf;

   451         }

   452         final long w10 = m1_00 * (long)s10 + m1_01 * (long)s11 + m1_02 * (long)s12;

   453         final long w11 = m1_10 * (long)s10 + m1_11 * (long)s11 + m1_12 * (long)s12;

   454         final long w12 = m1_20 * (long)s10 + m1_21 * (long)s11 + m1_22 * (long)s12;

   455         s10 = Math.floorMod(w10, (long)M1);

   456         s11 = Math.floorMod(w11, (long)M1);

   457         s12 = Math.floorMod(w12, (long)M1);

   458         final long w20 = m2_00 * (long)s20 + m2_01 * (long)s21 + m2_02 * (long)s22;

   459         final long w21 = m2_10 * (long)s20 + m2_11 * (long)s21 + m2_12 * (long)s22;

   460         final long w22 = m2_20 * (long)s20 + m2_21 * (long)s21 + m2_22 * (long)s22;

   461         s20 = Math.floorMod(w20, (long)M2);

   462         s21 = Math.floorMod(w21, (long)M2);

   463         s22 = Math.floorMod(w22, (long)M2);

   464     }

   465 

   466     /**

   467      * Alter the state of this pseudorandom number generator so as to

   468      * jump forward a distance equal to 2<sup>{@code logDistance}</sup>

   469      * within its state cycle.

   470      *

   471      * @param logDistance the base-2 logarithm of the distance to jump

   472      *        forward within the state cycle.  Must be non-negative and

   473      *        not greater than 192.

   474      *

   475      * @throws IllegalArgumentException if {@code logDistance} is

   476      *         less than zero or 2<sup>{@code logDistance}</sup> is

   477      *         greater than the period of this generator

   478      */

   479     public void jumpPowerOfTwo(int logDistance) {

   480         if (logDistance < 0 || logDistance > 192)

   481             throw new IllegalArgumentException("logDistance must be non-negative and not greater than 192");

   482         jump(Math.scalb(1.0, logDistance));

   483     }

   484 

   485 }