UUID.hpp

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#pragma once
#include <cstdint>
#include <functional>
#include <string_view>
#include "Hash.hpp"
 
namespace Foundation::Core {
    // http://www.jstatsoft.org/v08/i14/paper
    class XorShift128
    {
    public:
        XorShift128(uint64_t seed) noexcept { Reseed(seed); }
        XorShift128(uint64_t s0, uint64_t s1) noexcept { Reseed(s0, s1); }
        void Reseed(uint64_t seed) noexcept;
        // Seeds all 128 bits of state from two independent entropy words.
        void Reseed(uint64_t s0, uint64_t s1) noexcept;
        uint64_t Next() noexcept;
 
    private:
        uint64_t _x{ 0x9E3779B97F4A7C15ull };
        uint64_t _y{ 0xBF58476D1CE4E5B9ull };
        uint64_t _z{ 0x94D049BB133111EBull };
        uint64_t _w{ 0xFF51AFD7ED558CCDull };
    };
 
    struct FUUID
    {
        uint64_t hi{0};
        uint64_t lo{0};
 
        [[nodiscard]] bool IsNil() const noexcept { return hi == 0 && lo == 0; }
 
        friend bool operator==(FUUID, FUUID) noexcept = default;
        friend bool operator!=(FUUID, FUUID) noexcept = default;
        friend bool operator<(FUUID a, FUUID b) noexcept { return a.hi != b.hi ? a.hi < b.hi : a.lo < b.lo; }
        friend bool operator>(FUUID a, FUUID b) noexcept { return b < a; }
        friend bool operator<=(FUUID a, FUUID b) noexcept { return !(b < a); }
        friend bool operator>=(FUUID a, FUUID b) noexcept { return !(a < b); }
 
        [[nodiscard]] static FUUID Generate();
        [[nodiscard]] static FUUID FromBytes(const void* data, size_t size);
        [[nodiscard]] static FUUID FromString(std::string_view s) { return FromBytes(s.data(), s.size()); }
 
        // RFC 9562 canonical 8-4-4-4-12 lowercase hex; writes "nil" when @ref IsNil().
        [[nodiscard]] char const* Format(char* buf, size_t bufSize) const noexcept;
    };
 
    static constexpr FUUID kNilUUID{};
 
} // namespace Foundation::Core
 
template <>
struct std::hash<Foundation::Core::FUUID>
{
    size_t operator()(Foundation::Core::FUUID const& id) const noexcept
    {
        return static_cast<size_t>(Foundation::Core::FNV1a64(id.hi, id.lo));
    }
};