splitmix64.hpp

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#pragma once
 
#include <cstdint>
 
namespace randlib
{
 
class SplitMix64
{
public:
    using result_type = std::uint64_t;
 
    constexpr explicit SplitMix64(std::uint64_t seed = 0) noexcept : state(seed) {}
 
    static constexpr result_type min() noexcept { return 0; }
    static constexpr result_type max() noexcept { return ~result_type{0}; }
 
    constexpr void seed(std::uint64_t value) noexcept { state = value; }
 
    constexpr result_type operator()() noexcept
    {
        std::uint64_t z = (state += 0x9E3779B97F4A7C15ULL);
        z = (z ^ (z >> 30)) * 0xBF58476D1CE4E5B9ULL;
        z = (z ^ (z >> 27)) * 0x94D049BB133111EBULL;
        return z ^ (z >> 31);
    }
 
    constexpr void discard(unsigned long long n) noexcept { state += n * 0x9E3779B97F4A7C15ULL; }
 
    friend constexpr bool operator==(const SplitMix64 &, const SplitMix64 &) = default;
 
private:
    std::uint64_t state;
};
 
} // namespace randlib