A "jumpable and leapable" pseudorandom number generator (PRNG) whose period is roughly 2²⁵⁶. Class Xoshiro256PlusPlus implements interfaces RandomGenerator and LeapableGenerator, and therefore supports methods for producing pseudorandomly chosen values of type int, long, float, double, and boolean (and for producing streams of pseudorandomly chosen numbers of type int, long, and double), as well as methods for creating new Xoshiro256PlusPlus objects by moving forward either a large distance (2¹²⁸) or a very large distance (2¹⁹²) around the state cycle.

Series of generated values pass the TestU01 BigCrush and PractRand test suites that measure independence and uniformity properties of random number generators. (Most recently validated with version 1.2.3 of TestU01 and version 0.90 of PractRand. Note that TestU01 BigCrush was used to test not only values produced by the nextLong() method but also the result of bit-reversing each value produced by nextLong().) These tests validate only the methods for certain types and ranges, but similar properties are expected to hold, at least approximately, for others as well.

The class Xoshiro256PlusPlus uses the xoshiro256 algorithm, version 1.0 (parameters 17, 45), with the "++" scrambler that computes Long.rotateLeft(s0 + s3, 23) + s0. (See David Blackman and Sebastiano Vigna, "Scrambled Linear Pseudorandom Number Generators," ACM Transactions on Mathematical Software, 2021.) Its state consists of four long fields x0, x1, x2, and x3, which can take on any values provided that they are not all zero. The period of this generator is 2²⁵⁶-1.

The 64-bit values produced by the nextLong() method are equidistributed. To be precise, over the course of the cycle of length 2²⁵⁶-1, each nonzero long value is generated 2¹⁹² times, but the value 0 is generated only 2¹⁹²-1 times. The values produced by the nextInt(), nextFloat(), and nextDouble() methods are likewise equidistributed. Moreover, the 64-bit values produced by the nextLong() method are 3-equidistributed.

Instances Xoshiro256PlusPlus are not thread-safe. They are designed to be used so that each thread as its own instance. The methods jump and leap and jumps and leaps can be used to construct new instances of Xoshiro256PlusPlus that traverse other parts of the state cycle.

Instances of Xoshiro256PlusPlus are not cryptographically secure. Consider instead using java.security.SecureRandom in security-sensitive applications. Additionally, default-constructed instances do not use a cryptographically random seed unless the system property java.util.secureRandomSeed is set to true.