24  */

    24  */

    25 package java.util;

    25 package java.util;

    26 

    26 

    27 import java.math.BigInteger;

    27 import java.math.BigInteger;

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

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

    29 

    32 

    30 /**

    33 /**

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

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

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

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

    33  * generate subtasks. Class {@code SplittableRandom} supports methods for

    36  * generate subtasks. Class {@code SplittableRandom} supports methods for

    77  *

    80  *

    78  * @author  Guy Steele

    81  * @author  Guy Steele

    79  * @author  Doug Lea

    82  * @author  Doug Lea

    80  * @since   1.8

    83  * @since   1.8

    81  */

    84  */

    83 

    86 

    84     /*

    87     /*

    85      * Implementation Overview.

    88      * Implementation Overview.

    86      *

    89      *

    87      * This algorithm was inspired by the "DotMix" algorithm by

    90      * This algorithm was inspired by the "DotMix" algorithm by

   191     }

   194     }

   192 

   195 

   193     /**

   196     /**

   194      * Returns the gamma value to use for a new split instance.

   197      * Returns the gamma value to use for a new split instance.

   195      * Uses the 64bit mix function from MurmurHash3.

   198      * Uses the 64bit mix function from MurmurHash3.

   197      */

   200      */

   198     private static long mixGamma(long z) {

   201     private static long mixGamma(long z) {

   199         z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants

   202         z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants

   200         z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;

   203         z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;

   201         z = (z ^ (z >>> 33)) | 1L;                  // force to be odd

   204         z = (z ^ (z >>> 33)) | 1L;                  // force to be odd

   211     }

   214     }

   212 

   215 

   213     /**

   216     /**

   214      * The seed generator for default constructors.

   217      * The seed generator for default constructors.

   215      */

   218      */

   218     /* ---------------- public methods ---------------- */

   221     /* ---------------- public methods ---------------- */

   219 

   222 

   220     /**

   223     /**

   221      * Creates a new SplittableRandom instance using the specified

   224      * Creates a new SplittableRandom instance using the specified

   222      * initial seed. SplittableRandom instances created with the same

   225      * initial seed. SplittableRandom instances created with the same

   239         this.seed = mix64(s);

   242         this.seed = mix64(s);

   240         this.gamma = mixGamma(s + GOLDEN_GAMMA);

   243         this.gamma = mixGamma(s + GOLDEN_GAMMA);

   241     }

   244     }

   242 

   245 

   243     //    public SplittableRandom copy() { return new SplittableRandom(seed, gamma); }

   246     //    public SplittableRandom copy() { return new SplittableRandom(seed, gamma); }

   245     /**

   248     /**

   246      * Constructs and returns a new SplittableRandom instance that

   249      * Constructs and returns a new SplittableRandom instance that

   247      * shares no mutable state with this instance. However, with very

   250      * shares no mutable state with this instance. However, with very

   248      * high probability, the set of values collectively generated by

   251      * high probability, the set of values collectively generated by

   249      * the two objects has the same statistical properties as if the

   252      * the two objects has the same statistical properties as if the

   258      */

   261      */

   259     public SplittableRandom split() {

   262     public SplittableRandom split() {

   260         return new SplittableRandom(nextLong(), mixGamma(nextSeed()));

   263         return new SplittableRandom(nextLong(), mixGamma(nextSeed()));

   261     }

   264     }

   262 

   265 

   264         return new SplittableRandom(source.nextLong(), mixGamma(source.nextLong()));

   267         return new SplittableRandom(source.nextLong(), mixGamma(source.nextLong()));

   265     }

   268     }

   266 

   269 

   267     /**

   270     /**

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

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