xoshiro128starstar.hpp

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// SPDX-License-Identifier: BSL-1.0
 
#ifndef TETL_RANDOM_XORSHIFT128STARSTAR_HPP
#define TETL_RANDOM_XORSHIFT128STARSTAR_HPP
 
#include <etl/_algorithm/equal.hpp>
#include <etl/_bit/rotl.hpp>
#include <etl/_cstdint/uint_t.hpp>
#include <etl/_iterator/begin.hpp>
#include <etl/_iterator/end.hpp>
#include <etl/_limits/numeric_limits.hpp>
 
namespace etl {

struct xoshiro128starstar {
    using result_type                  = uint32_t;
    static constexpr auto default_seed = result_type{5489U};
 
    constexpr xoshiro128starstar() = default;
 
    explicit constexpr xoshiro128starstar(result_type seed) noexcept
        : _state{seed}
    {
    }
 
    [[nodiscard]] static constexpr auto min() noexcept -> result_type { return numeric_limits<uint32_t>::min(); }
 
    [[nodiscard]] static constexpr auto max() noexcept -> result_type { return numeric_limits<uint32_t>::max() - 1; }
 
    constexpr auto seed(result_type value = default_seed) noexcept -> void { _state[0] = value; }
 
    constexpr auto discard(unsigned long long z) noexcept -> void
    {
        for (auto i{0ULL}; i < z; ++i) {
            (void)(*this)();
        }
    }
 
    [[nodiscard]] constexpr auto operator()() noexcept -> result_type
    {
        uint32_t const result = rotl(_state[1] * 5, 7) * 9;
        uint32_t const t      = _state[1] << 9;
 
        _state[2] ^= _state[0];
        _state[3] ^= _state[1];
        _state[1] ^= _state[2];
        _state[0] ^= _state[3];
 
        _state[2] ^= t;
 
        _state[3] = rotl(_state[3], 11);
 
        return result;
    }
 
    [[nodiscard]] friend constexpr auto
    operator==(xoshiro128starstar const& lhs, xoshiro128starstar const& rhs) noexcept -> bool
    {
        return equal(begin(lhs._state), end(lhs._state), begin(rhs._state), end(rhs._state));
    }
 
    [[nodiscard]] friend constexpr auto
    operator!=(xoshiro128starstar const& lhs, xoshiro128starstar const& rhs) noexcept -> bool
    {
        return !(lhs == rhs);
    }
 
private:
    uint32_t _state[4]{default_seed};
};
 
} // namespace etl
 
#endif // TETL_RANDOM_XORSHIFT128STARSTAR_HPP