kuiper-engine/include/utils/xoshiro256plusplus.hpp

#pragma once

#include <array>
#include <cstdint>
#include <random>

namespace kuiper::random
{

class xoshiro256pp {
  public:
    xoshiro256pp(const std::array<std::uint64_t, 4>& state)
        : s(state) {}

    static xoshiro256pp from_random_device() {
        std::random_device rd {};

        static_assert(sizeof(std::random_device::result_type) == 4);

        const std::uint64_t a = static_cast<std::uint64_t>(rd()) << 32 | static_cast<std::uint64_t>(rd());
        const std::uint64_t b = static_cast<std::uint64_t>(rd()) << 32 | static_cast<std::uint64_t>(rd());
        const std::uint64_t c = static_cast<std::uint64_t>(rd()) << 32 | static_cast<std::uint64_t>(rd());
        const std::uint64_t d = static_cast<std::uint64_t>(rd()) << 32 | static_cast<std::uint64_t>(rd());

        return {{{a, b, c, d}}};
    }

  public:
    std::uint64_t next() noexcept {
        const std::uint64_t result = rotl(s[0] + s[3], 23) + s[0];

        const std::uint64_t t = s[1] << 17;

        s[2] ^= s[0];
        s[3] ^= s[1];
        s[1] ^= s[2];
        s[0] ^= s[3];

        s[2] ^= t;

        s[3] = rotl(s[3], 45);

        return result;
    }

    std::uint64_t operator()(void) noexcept {
        return next();
    }

  private:
    /* This is the jump function for the generator. It is equivalent
       to 2^128 calls to next(); it can be used to generate 2^128
       non-overlapping subsequences for parallel computations. */

    void jump() noexcept {
        static constexpr std::array<std::uint64_t, 4> JUMP = {
            0x180ec6d33cfd0aba, 0xd5a61266f0c9392c, 0xa9582618e03fc9aa, 0x39abdc4529b1661c};

        std::uint64_t s0 = 0;
        std::uint64_t s1 = 0;
        std::uint64_t s2 = 0;
        std::uint64_t s3 = 0;
        for (int i = 0; i < JUMP.size() / sizeof(std::uint64_t); i++)
            for (int b = 0; b < 64; b++) {
                if (JUMP[i] & UINT64_C(1) << b) {
                    s0 ^= s[0];
                    s1 ^= s[1];
                    s2 ^= s[2];
                    s3 ^= s[3];
                }
                next();
            }

        s[0] = s0;
        s[1] = s1;
        s[2] = s2;
        s[3] = s3;
    }

    /* This is the long-jump function for the generator. It is equivalent to
       2^192 calls to next(); it can be used to generate 2^64 starting points,
       from each of which jump() will generate 2^64 non-overlapping
       subsequences for parallel distributed computations. */

    void long_jump() {
        static constexpr std::array<std::uint64_t, 4> LONG_JUMP = {
            0x76e15d3efefdcbbf, 0xc5004e441c522fb3, 0x77710069854ee241, 0x39109bb02acbe635};

        std::uint64_t s0 = 0;
        std::uint64_t s1 = 0;
        std::uint64_t s2 = 0;
        std::uint64_t s3 = 0;
        for (int i = 0; i < LONG_JUMP.size() / sizeof(std::uint64_t); i++)
            for (int b = 0; b < 64; b++) {
                if (LONG_JUMP[i] & UINT64_C(1) << b) {
                    s0 ^= s[0];
                    s1 ^= s[1];
                    s2 ^= s[2];
                    s3 ^= s[3];
                }
                next();
            }

        s[0] = s0;
        s[1] = s1;
        s[2] = s2;
        s[3] = s3;
    }

    inline std::uint64_t rotl(const std::uint64_t x, int k) {
        return (x << k) | (x >> (64 - k));
    }

  private:
    std::array<std::uint64_t, 4> s {};
};

// Original license & preface:

/*  Written in 2019 by David Blackman and Sebastiano Vigna (vigna@acm.org)

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.

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

/* This is xoshiro256++ 1.0, one of our all-purpose, rock-solid generators.
   It has excellent (sub-ns) speed, a state (256 bits) that is large
   enough for any parallel application, and it passes all tests we are
   aware of.

   For generating just floating-point numbers, xoshiro256+ is even 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. */

} // namespace kuiper::random