///////////////////////// ankerl::unordered_dense::{map, set} /////////////////////////

// A fast & densely stored hashmap and hashset based on robin-hood backward shift deletion.
// Version 4.1.2
// https://github.com/martinus/unordered_dense
//
// Licensed under the MIT License <http://opensource.org/licenses/MIT>.
// SPDX-License-Identifier: MIT
// Copyright (c) 2022-2023 Martin Leitner-Ankerl <martin.ankerl@gmail.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#ifndef ANKERL_UNORDERED_DENSE_H
#define ANKERL_UNORDERED_DENSE_H

// see https://semver.org/spec/v2.0.0.html
#define ANKERL_UNORDERED_DENSE_VERSION_MAJOR 4 // NOLINT(cppcoreguidelines-macro-usage) incompatible API changes
#define ANKERL_UNORDERED_DENSE_VERSION_MINOR 1 // NOLINT(cppcoreguidelines-macro-usage) backwards compatible functionality
#define ANKERL_UNORDERED_DENSE_VERSION_PATCH 2 // NOLINT(cppcoreguidelines-macro-usage) backwards compatible bug fixes

// API versioning with inline namespace, see https://www.foonathan.net/2018/11/inline-namespaces/

// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
#define ANKERL_UNORDERED_DENSE_VERSION_CONCAT1(major, minor, patch) v##major##_##minor##_##patch
// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
#define ANKERL_UNORDERED_DENSE_VERSION_CONCAT(major, minor, patch) ANKERL_UNORDERED_DENSE_VERSION_CONCAT1(major, minor, patch)
#define ANKERL_UNORDERED_DENSE_NAMESPACE   \
    ANKERL_UNORDERED_DENSE_VERSION_CONCAT( \
        ANKERL_UNORDERED_DENSE_VERSION_MAJOR, ANKERL_UNORDERED_DENSE_VERSION_MINOR, ANKERL_UNORDERED_DENSE_VERSION_PATCH)

#if defined(_MSVC_LANG)
#define ANKERL_UNORDERED_DENSE_CPP_VERSION _MSVC_LANG
#else
#define ANKERL_UNORDERED_DENSE_CPP_VERSION __cplusplus
#endif

#if defined(__GNUC__)
// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
#define ANKERL_UNORDERED_DENSE_PACK(decl) decl __attribute__((__packed__))
#elif defined(_MSC_VER)
// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
#define ANKERL_UNORDERED_DENSE_PACK(decl) __pragma(pack(push, 1)) decl __pragma(pack(pop))
#endif

// exceptions
#if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)
#define ANKERL_UNORDERED_DENSE_HAS_EXCEPTIONS() 1 // NOLINT(cppcoreguidelines-macro-usage)
#else
#define ANKERL_UNORDERED_DENSE_HAS_EXCEPTIONS() 0 // NOLINT(cppcoreguidelines-macro-usage)
#endif
#ifdef _MSC_VER
#define ANKERL_UNORDERED_DENSE_NOINLINE __declspec(noinline)
#else
#define ANKERL_UNORDERED_DENSE_NOINLINE __attribute__((noinline))
#endif

// defined in unordered_dense.cpp
#if !defined(ANKERL_UNORDERED_DENSE_EXPORT)
#define ANKERL_UNORDERED_DENSE_EXPORT
#endif

#if ANKERL_UNORDERED_DENSE_CPP_VERSION < 201703L
#error ankerl::unordered_dense requires C++17 or higher
#else
#include <array>            // for array
#include <cstdint>          // for uint64_t, uint32_t, uint8_t, UINT64_C
#include <cstring>          // for size_t, memcpy, memset
#include <functional>       // for equal_to, hash
#include <initializer_list> // for initializer_list
#include <iterator>         // for pair, distance
#include <limits>           // for numeric_limits
#include <memory>           // for allocator, allocator_traits, shared_ptr
#include <stdexcept>        // for out_of_range
#include <string>           // for basic_string
#include <string_view>      // for basic_string_view, hash
#include <tuple>            // for forward_as_tuple
#include <type_traits>      // for enable_if_t, declval, conditional_t, ena...
#include <utility>          // for forward, exchange, pair, as_const, piece...
#include <vector>           // for vector
#if ANKERL_UNORDERED_DENSE_HAS_EXCEPTIONS() == 0
#include <cstdlib> // for abort
#endif

#if defined(__has_include)
#if __has_include(<memory_resource>)
#define ANKERL_UNORDERED_DENSE_PMR std::pmr // NOLINT(cppcoreguidelines-macro-usage)
#include <memory_resource>                  // for polymorphic_allocator
#elif __has_include(<experimental/memory_resource>)
#define ANKERL_UNORDERED_DENSE_PMR std::experimental::pmr // NOLINT(cppcoreguidelines-macro-usage)
#include <experimental/memory_resource>                   // for polymorphic_allocator
#endif
#endif

#if defined(_MSC_VER) && defined(_M_X64)
#include <intrin.h>
#pragma intrinsic(_umul128)
#endif

#if defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__clang__)
#define ANKERL_UNORDERED_DENSE_LIKELY(x) __builtin_expect(x, 1)   // NOLINT(cppcoreguidelines-macro-usage)
#define ANKERL_UNORDERED_DENSE_UNLIKELY(x) __builtin_expect(x, 0) // NOLINT(cppcoreguidelines-macro-usage)
#else
#define ANKERL_UNORDERED_DENSE_LIKELY(x) (x)   // NOLINT(cppcoreguidelines-macro-usage)
#define ANKERL_UNORDERED_DENSE_UNLIKELY(x) (x) // NOLINT(cppcoreguidelines-macro-usage)
#endif

namespace ankerl::unordered_dense
{
    inline namespace ANKERL_UNORDERED_DENSE_NAMESPACE
    {

        namespace detail
        {

#if ANKERL_UNORDERED_DENSE_HAS_EXCEPTIONS()

            // make sure this is not inlined as it is slow and dramatically enlarges code, thus making other
            // inlinings more difficult. Throws are also generally the slow path.
            [[noreturn]] inline ANKERL_UNORDERED_DENSE_NOINLINE void on_error_key_not_found()
            {
                throw std::out_of_range("ankerl::unordered_dense::map::at(): key not found");
            }
            [[noreturn]] inline ANKERL_UNORDERED_DENSE_NOINLINE void on_error_bucket_overflow()
            {
                throw std::overflow_error("ankerl::unordered_dense: reached max bucket size, cannot increase size");
            }
            [[noreturn]] inline ANKERL_UNORDERED_DENSE_NOINLINE void on_error_too_many_elements()
            {
                throw std::out_of_range("ankerl::unordered_dense::map::replace(): too many elements");
            }

#else

            [[noreturn]] inline void on_error_key_not_found()
            {
                abort();
            }
            [[noreturn]] inline void on_error_bucket_overflow()
            {
                abort();
            }
            [[noreturn]] inline void on_error_too_many_elements()
            {
                abort();
            }

#endif

        } // namespace detail

        // hash ///////////////////////////////////////////////////////////////////////

        // This is a stripped-down implementation of wyhash: https://github.com/wangyi-fudan/wyhash
        // No big-endian support (because different values on different machines don't matter),
        // hardcodes seed and the secret, reformats the code, and clang-tidy fixes.
        namespace detail::wyhash
        {

            inline void mum(uint64_t *a, uint64_t *b)
            {
#if defined(__SIZEOF_INT128__)
                __uint128_t r = *a;
                r *= *b;
                *a = static_cast<uint64_t>(r);
                *b = static_cast<uint64_t>(r >> 64U);
#elif defined(_MSC_VER) && defined(_M_X64)
                *a = _umul128(*a, *b, b);
#else
                uint64_t ha = *a >> 32U;
                uint64_t hb = *b >> 32U;
                uint64_t la = static_cast<uint32_t>(*a);
                uint64_t lb = static_cast<uint32_t>(*b);
                uint64_t hi{};
                uint64_t lo{};
                uint64_t rh = ha * hb;
                uint64_t rm0 = ha * lb;
                uint64_t rm1 = hb * la;
                uint64_t rl = la * lb;
                uint64_t t = rl + (rm0 << 32U);
                auto c = static_cast<uint64_t>(t < rl);
                lo = t + (rm1 << 32U);
                c += static_cast<uint64_t>(lo < t);
                hi = rh + (rm0 >> 32U) + (rm1 >> 32U) + c;
                *a = lo;
                *b = hi;
#endif
            }

            // multiply and xor mix function, aka MUM
            [[nodiscard]] inline auto mix(uint64_t a, uint64_t b) -> uint64_t
            {
                mum(&a, &b);
                return a ^ b;
            }

            // read functions. WARNING: we don't care about endianness, so results are different on big endian!
            [[nodiscard]] inline auto r8(const uint8_t *p) -> uint64_t
            {
                uint64_t v{};
                std::memcpy(&v, p, 8U);
                return v;
            }

            [[nodiscard]] inline auto r4(const uint8_t *p) -> uint64_t
            {
                uint32_t v{};
                std::memcpy(&v, p, 4);
                return v;
            }

            // reads 1, 2, or 3 bytes
            [[nodiscard]] inline auto r3(const uint8_t *p, size_t k) -> uint64_t
            {
                return (static_cast<uint64_t>(p[0]) << 16U) | (static_cast<uint64_t>(p[k >> 1U]) << 8U) | p[k - 1];
            }

            [[maybe_unused]] [[nodiscard]] inline auto hash(void const *key, size_t len) -> uint64_t
            {
                static constexpr auto secret = std::array{UINT64_C(0xa0761d6478bd642f),
                                                          UINT64_C(0xe7037ed1a0b428db),
                                                          UINT64_C(0x8ebc6af09c88c6e3),
                                                          UINT64_C(0x589965cc75374cc3)};

                auto const *p = static_cast<uint8_t const *>(key);
                uint64_t seed = secret[0];
                uint64_t a{};
                uint64_t b{};
                if (ANKERL_UNORDERED_DENSE_LIKELY(len <= 16))
                {
                    if (ANKERL_UNORDERED_DENSE_LIKELY(len >= 4))
                    {
                        a = (r4(p) << 32U) | r4(p + ((len >> 3U) << 2U));
                        b = (r4(p + len - 4) << 32U) | r4(p + len - 4 - ((len >> 3U) << 2U));
                    }
                    else if (ANKERL_UNORDERED_DENSE_LIKELY(len > 0))
                    {
                        a = r3(p, len);
                        b = 0;
                    }
                    else
                    {
                        a = 0;
                        b = 0;
                    }
                }
                else
                {
                    size_t i = len;
                    if (ANKERL_UNORDERED_DENSE_UNLIKELY(i > 48))
                    {
                        uint64_t see1 = seed;
                        uint64_t see2 = seed;
                        do
                        {
                            seed = mix(r8(p) ^ secret[1], r8(p + 8) ^ seed);
                            see1 = mix(r8(p + 16) ^ secret[2], r8(p + 24) ^ see1);
                            see2 = mix(r8(p + 32) ^ secret[3], r8(p + 40) ^ see2);
                            p += 48;
                            i -= 48;
                        } while (ANKERL_UNORDERED_DENSE_LIKELY(i > 48));
                        seed ^= see1 ^ see2;
                    }
                    while (ANKERL_UNORDERED_DENSE_UNLIKELY(i > 16))
                    {
                        seed = mix(r8(p) ^ secret[1], r8(p + 8) ^ seed);
                        i -= 16;
                        p += 16;
                    }
                    a = r8(p + i - 16);
                    b = r8(p + i - 8);
                }

                return mix(secret[1] ^ len, mix(a ^ secret[1], b ^ seed));
            }

            [[nodiscard]] inline auto hash(uint64_t x) -> uint64_t
            {
                return detail::wyhash::mix(x, UINT64_C(0x9E3779B97F4A7C15));
            }

        } // namespace detail::wyhash

        ANKERL_UNORDERED_DENSE_EXPORT template <typename T, typename Enable = void>
        struct hash
        {
            auto operator()(T const &obj) const noexcept(noexcept(std::declval<std::hash<T>>().operator()(std::declval<T const &>())))
                -> uint64_t
            {
                return std::hash<T>{}(obj);
            }
        };

        template <typename CharT>
        struct hash<std::basic_string<CharT>>
        {
            using is_avalanching = void;
            auto operator()(std::basic_string<CharT> const &str) const noexcept -> uint64_t
            {
                return detail::wyhash::hash(str.data(), sizeof(CharT) * str.size());
            }
        };

        template <typename CharT>
        struct hash<std::basic_string_view<CharT>>
        {
            using is_avalanching = void;
            auto operator()(std::basic_string_view<CharT> const &sv) const noexcept -> uint64_t
            {
                return detail::wyhash::hash(sv.data(), sizeof(CharT) * sv.size());
            }
        };

        template <class T>
        struct hash<T *>
        {
            using is_avalanching = void;
            auto operator()(T *ptr) const noexcept -> uint64_t
            {
                // NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
                return detail::wyhash::hash(reinterpret_cast<uintptr_t>(ptr));
            }
        };

        template <class T>
        struct hash<std::unique_ptr<T>>
        {
            using is_avalanching = void;
            auto operator()(std::unique_ptr<T> const &ptr) const noexcept -> uint64_t
            {
                // NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
                return detail::wyhash::hash(reinterpret_cast<uintptr_t>(ptr.get()));
            }
        };

        template <class T>
        struct hash<std::shared_ptr<T>>
        {
            using is_avalanching = void;
            auto operator()(std::shared_ptr<T> const &ptr) const noexcept -> uint64_t
            {
                // NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
                return detail::wyhash::hash(reinterpret_cast<uintptr_t>(ptr.get()));
            }
        };

        template <typename Enum>
        struct hash<Enum, typename std::enable_if<std::is_enum<Enum>::value>::type>
        {
            using is_avalanching = void;
            auto operator()(Enum e) const noexcept -> uint64_t
            {
                using underlying = typename std::underlying_type_t<Enum>;
                return detail::wyhash::hash(static_cast<underlying>(e));
            }
        };

// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
#define ANKERL_UNORDERED_DENSE_HASH_STATICCAST(T)                    \
    template <>                                                      \
    struct hash<T>                                                   \
    {                                                                \
        using is_avalanching = void;                                 \
        auto operator()(T const &obj) const noexcept -> uint64_t     \
        {                                                            \
            return detail::wyhash::hash(static_cast<uint64_t>(obj)); \
        }                                                            \
    }

#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuseless-cast"
#endif
        // see https://en.cppreference.com/w/cpp/utility/hash
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(bool);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(char);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(signed char);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(unsigned char);
#if ANKERL_UNORDERED_DENSE_CPP_VERSION >= 202002L && defined(__cpp_char8_t)
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(char8_t);
#endif
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(char16_t);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(char32_t);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(wchar_t);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(short);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(unsigned short);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(int);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(unsigned int);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(long);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(long long);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(unsigned long);
        ANKERL_UNORDERED_DENSE_HASH_STATICCAST(unsigned long long);

#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic pop
#endif

        // bucket_type //////////////////////////////////////////////////////////

        namespace bucket_type
        {

            struct standard
            {
                static constexpr uint32_t dist_inc = 1U << 8U;             // skip 1 byte fingerprint
                static constexpr uint32_t fingerprint_mask = dist_inc - 1; // mask for 1 byte of fingerprint

                uint32_t m_dist_and_fingerprint; // upper 3 byte: distance to original bucket. lower byte: fingerprint from hash
                uint32_t m_value_idx;            // index into the m_values vector.
            };

            ANKERL_UNORDERED_DENSE_PACK(struct big {
                static constexpr uint32_t dist_inc = 1U << 8U;             // skip 1 byte fingerprint
                static constexpr uint32_t fingerprint_mask = dist_inc - 1; // mask for 1 byte of fingerprint

                uint32_t m_dist_and_fingerprint; // upper 3 byte: distance to original bucket. lower byte: fingerprint from hash
                size_t m_value_idx;              // index into the m_values vector.
            });

        } // namespace bucket_type

        namespace detail
        {

            struct nonesuch
            {
            };

            template <class Default, class AlwaysVoid, template <class...> class Op, class... Args>
            struct detector
            {
                using value_t = std::false_type;
                using type = Default;
            };

            template <class Default, template <class...> class Op, class... Args>
            struct detector<Default, std::void_t<Op<Args...>>, Op, Args...>
            {
                using value_t = std::true_type;
                using type = Op<Args...>;
            };

            template <template <class...> class Op, class... Args>
            using is_detected = typename detail::detector<detail::nonesuch, void, Op, Args...>::value_t;

            template <template <class...> class Op, class... Args>
            constexpr bool is_detected_v = is_detected<Op, Args...>::value;

            template <typename T>
            using detect_avalanching = typename T::is_avalanching;

            template <typename T>
            using detect_is_transparent = typename T::is_transparent;

            template <typename T>
            using detect_iterator = typename T::iterator;

            template <typename T>
            using detect_reserve = decltype(std::declval<T &>().reserve(size_t{}));

            // enable_if helpers

            template <typename Mapped>
            constexpr bool is_map_v = !std::is_void_v<Mapped>;

            // clang-format off
template <typename Hash, typename KeyEqual>
constexpr bool is_transparent_v = is_detected_v<detect_is_transparent, Hash> && is_detected_v<detect_is_transparent, KeyEqual>;
            // clang-format on

            template <typename From, typename To1, typename To2>
            constexpr bool is_neither_convertible_v = !std::is_convertible_v<From, To1> && !std::is_convertible_v<From, To2>;

            template <typename T>
            constexpr bool has_reserve = is_detected_v<detect_reserve, T>;

            // base type for map has mapped_type
            template <class T>
            struct base_table_type_map
            {
                using mapped_type = T;
            };

            // base type for set doesn't have mapped_type
            struct base_table_type_set
            {
            };

        } // namespace detail

        // Very much like std::deque, but faster for indexing (in most cases). As of now this doesn't implement the full std::vector
        // API, but merely what's necessary to work as an underlying container for ankerl::unordered_dense::{map, set}.
        // It allocates blocks of equal size and puts them into the m_blocks vector. That means it can grow simply by adding a new
        // block to the back of m_blocks, and doesn't double its size like an std::vector. The disadvantage is that memory is not
        // linear and thus there is one more indirection necessary for indexing.
        template <typename T, typename Allocator = std::allocator<T>, size_t MaxSegmentSizeBytes = 4096>
        class segmented_vector
        {
            template <bool IsConst>
            class iter_t;

        public:
            using allocator_type = Allocator;
            using pointer = typename std::allocator_traits<allocator_type>::pointer;
            using const_pointer = typename std::allocator_traits<allocator_type>::const_pointer;
            using difference_type = typename std::allocator_traits<allocator_type>::difference_type;
            using value_type = T;
            using size_type = std::size_t;
            using reference = T &;
            using const_reference = T const &;
            using iterator = iter_t<false>;
            using const_iterator = iter_t<true>;

        private:
            using vec_alloc = typename std::allocator_traits<Allocator>::template rebind_alloc<pointer>;
            std::vector<pointer, vec_alloc> m_blocks{};
            size_t m_size{};

            // Calculates the maximum number for x in  (s << x) <= max_val
            static constexpr auto num_bits_closest(size_t max_val, size_t s) -> size_t
            {
                auto f = size_t{0};
                while (s << (f + 1) <= max_val)
                {
                    ++f;
                }
                return f;
            }

            using self_t = segmented_vector<T, Allocator, MaxSegmentSizeBytes>;
            static constexpr auto num_bits = num_bits_closest(MaxSegmentSizeBytes, sizeof(T));
            static constexpr auto num_elements_in_block = 1U << num_bits;
            static constexpr auto mask = num_elements_in_block - 1U;

            /**
             * Iterator class doubles as const_iterator and iterator
             */
            template <bool IsConst>
            class iter_t
            {
                using ptr_t = typename std::conditional_t<IsConst, segmented_vector::const_pointer const *, segmented_vector::pointer *>;
                ptr_t m_data{};
                size_t m_idx{};

                template <bool B>
                friend class iter_t;

            public:
                using difference_type = segmented_vector::difference_type;
                using value_type = T;
                using reference = typename std::conditional_t<IsConst, value_type const &, value_type &>;
                using pointer = typename std::conditional_t<IsConst, segmented_vector::const_pointer, segmented_vector::pointer>;
                using iterator_category = std::forward_iterator_tag;

                iter_t() noexcept = default;

                template <bool OtherIsConst, typename = typename std::enable_if<IsConst && !OtherIsConst>::type>
                // NOLINTNEXTLINE(google-explicit-constructor,hicpp-explicit-conversions)
                constexpr iter_t(iter_t<OtherIsConst> const &other) noexcept
                    : m_data(other.m_data), m_idx(other.m_idx)
                {
                }

                constexpr iter_t(ptr_t data, size_t idx) noexcept
                    : m_data(data), m_idx(idx) {}

                template <bool OtherIsConst, typename = typename std::enable_if<IsConst && !OtherIsConst>::type>
                constexpr auto operator=(iter_t<OtherIsConst> const &other) noexcept -> iter_t &
                {
                    m_data = other.m_data;
                    m_idx = other.m_idx;
                    return *this;
                }

                constexpr auto operator++() noexcept -> iter_t &
                {
                    ++m_idx;
                    return *this;
                }

                constexpr auto operator+(difference_type diff) noexcept -> iter_t
                {
                    return {m_data, static_cast<size_t>(static_cast<difference_type>(m_idx) + diff)};
                }

                template <bool OtherIsConst>
                constexpr auto operator-(iter_t<OtherIsConst> const &other) noexcept -> difference_type
                {
                    return static_cast<difference_type>(m_idx) - static_cast<difference_type>(other.m_idx);
                }

                constexpr auto operator*() const noexcept -> reference
                {
                    return m_data[m_idx >> num_bits][m_idx & mask];
                }

                constexpr auto operator->() const noexcept -> pointer
                {
                    return &m_data[m_idx >> num_bits][m_idx & mask];
                }

                template <bool O>
                constexpr auto operator==(iter_t<O> const &o) const noexcept -> bool
                {
                    return m_idx == o.m_idx;
                }

                template <bool O>
                constexpr auto operator!=(iter_t<O> const &o) const noexcept -> bool
                {
                    return !(*this == o);
                }
            };

            // slow path: need to allocate a new segment every once in a while
            void increase_capacity()
            {
                auto ba = Allocator(m_blocks.get_allocator());
                pointer block = std::allocator_traits<Allocator>::allocate(ba, num_elements_in_block);
                m_blocks.push_back(block);
            }

            // Moves everything from other
            void append_everything_from(segmented_vector &&other)
            {
                reserve(size() + other.size());
                for (auto &&o : other)
                {
                    emplace_back(std::move(o));
                }
            }

            // Copies everything from other
            void append_everything_from(segmented_vector const &other)
            {
                reserve(size() + other.size());
                for (auto const &o : other)
                {
                    emplace_back(o);
                }
            }

            void dealloc()
            {
                auto ba = Allocator(m_blocks.get_allocator());
                for (auto ptr : m_blocks)
                {
                    std::allocator_traits<Allocator>::deallocate(ba, ptr, num_elements_in_block);
                }
            }

            [[nodiscard]] static constexpr auto calc_num_blocks_for_capacity(size_t capacity)
            {
                return (capacity + num_elements_in_block - 1U) / num_elements_in_block;
            }

        public:
            segmented_vector() = default;

            // NOLINTNEXTLINE(google-explicit-constructor,hicpp-explicit-conversions)
            segmented_vector(Allocator alloc)
                : m_blocks(vec_alloc(alloc)) {}

            segmented_vector(segmented_vector &&other, Allocator alloc)
                : segmented_vector(alloc)
            {
                *this = std::move(other);
            }

            segmented_vector(segmented_vector const &other, Allocator alloc)
                : m_blocks(vec_alloc(alloc))
            {
                append_everything_from(other);
            }

            segmented_vector(segmented_vector &&other) noexcept
                : segmented_vector(std::move(other), get_allocator()) {}

            segmented_vector(segmented_vector const &other)
            {
                append_everything_from(other);
            }

            auto operator=(segmented_vector const &other) -> segmented_vector &
            {
                if (this == &other)
                {
                    return *this;
                }
                clear();
                append_everything_from(other);
                return *this;
            }

            auto operator=(segmented_vector &&other) noexcept -> segmented_vector &
            {
                clear();
                dealloc();
                if (other.get_allocator() == get_allocator())
                {
                    m_blocks = std::move(other.m_blocks);
                    m_size = std::exchange(other.m_size, {});
                }
                else
                {
                    // make sure to construct with other's allocator!
                    m_blocks = std::vector<pointer, vec_alloc>(vec_alloc(other.get_allocator()));
                    append_everything_from(std::move(other));
                }
                return *this;
            }

            ~segmented_vector()
            {
                clear();
                dealloc();
            }

            [[nodiscard]] constexpr auto size() const -> size_t
            {
                return m_size;
            }

            [[nodiscard]] constexpr auto capacity() const -> size_t
            {
                return m_blocks.size() * num_elements_in_block;
            }

            // Indexing is highly performance critical
            [[nodiscard]] constexpr auto operator[](size_t i) const noexcept -> T const &
            {
                return m_blocks[i >> num_bits][i & mask];
            }

            [[nodiscard]] constexpr auto operator[](size_t i) noexcept -> T &
            {
                return m_blocks[i >> num_bits][i & mask];
            }

            [[nodiscard]] constexpr auto begin() -> iterator
            {
                return {m_blocks.data(), 0U};
            }
            [[nodiscard]] constexpr auto begin() const -> const_iterator
            {
                return {m_blocks.data(), 0U};
            }
            [[nodiscard]] constexpr auto cbegin() const -> const_iterator
            {
                return {m_blocks.data(), 0U};
            }

            [[nodiscard]] constexpr auto end() -> iterator
            {
                return {m_blocks.data(), m_size};
            }
            [[nodiscard]] constexpr auto end() const -> const_iterator
            {
                return {m_blocks.data(), m_size};
            }
            [[nodiscard]] constexpr auto cend() const -> const_iterator
            {
                return {m_blocks.data(), m_size};
            }

            [[nodiscard]] constexpr auto back() -> reference
            {
                return operator[](m_size - 1);
            }
            [[nodiscard]] constexpr auto back() const -> const_reference
            {
                return operator[](m_size - 1);
            }

            void pop_back()
            {
                back().~T();
                --m_size;
            }

            [[nodiscard]] auto empty() const
            {
                return 0 == m_size;
            }

            void reserve(size_t new_capacity)
            {
                m_blocks.reserve(calc_num_blocks_for_capacity(new_capacity));
                while (new_capacity > capacity())
                {
                    increase_capacity();
                }
            }

            [[nodiscard]] auto get_allocator() const -> allocator_type
            {
                return allocator_type{m_blocks.get_allocator()};
            }

            template <class... Args>
            auto emplace_back(Args &&...args) -> reference
            {
                if (m_size == capacity())
                {
                    increase_capacity();
                }
                auto *ptr = static_cast<void *>(&operator[](m_size));
                auto &ref = *new (ptr) T(std::forward<Args>(args)...);
                ++m_size;
                return ref;
            }

            void clear()
            {
                if constexpr (!std::is_trivially_destructible_v<T>)
                {
                    for (size_t i = 0, s = size(); i < s; ++i)
                    {
                        operator[](i).~T();
                    }
                }
                m_size = 0;
            }

            void shrink_to_fit()
            {
                auto ba = Allocator(m_blocks.get_allocator());
                auto num_blocks_required = calc_num_blocks_for_capacity(m_size);
                while (m_blocks.size() > num_blocks_required)
                {
                    std::allocator_traits<Allocator>::deallocate(ba, m_blocks.back(), num_elements_in_block);
                    m_blocks.pop_back();
                }
                m_blocks.shrink_to_fit();
            }
        };

        namespace detail
        {

            // This is it, the table. Doubles as map and set, and uses `void` for T when its used as a set.
            template <class Key,
                      class T, // when void, treat it as a set.
                      class Hash,
                      class KeyEqual,
                      class AllocatorOrContainer,
                      class Bucket,
                      bool IsSegmented>
            class table : public std::conditional_t<is_map_v<T>, base_table_type_map<T>, base_table_type_set>
            {
                using underlying_value_type = typename std::conditional_t<is_map_v<T>, std::pair<Key, T>, Key>;
                using underlying_container_type = std::conditional_t<IsSegmented,
                                                                     segmented_vector<underlying_value_type, AllocatorOrContainer>,
                                                                     std::vector<underlying_value_type, AllocatorOrContainer>>;

            public:
                using value_container_type = std::
                    conditional_t<is_detected_v<detect_iterator, AllocatorOrContainer>, AllocatorOrContainer, underlying_container_type>;

            private:
                using bucket_alloc =
                    typename std::allocator_traits<typename value_container_type::allocator_type>::template rebind_alloc<Bucket>;
                using bucket_alloc_traits = std::allocator_traits<bucket_alloc>;

                static constexpr uint8_t initial_shifts = 64 - 3; // 2^(64-m_shift) number of buckets
                static constexpr float default_max_load_factor = 0.8F;

            public:
                using key_type = Key;
                using value_type = typename value_container_type::value_type;
                using size_type = typename value_container_type::size_type;
                using difference_type = typename value_container_type::difference_type;
                using hasher = Hash;
                using key_equal = KeyEqual;
                using allocator_type = typename value_container_type::allocator_type;
                using reference = typename value_container_type::reference;
                using const_reference = typename value_container_type::const_reference;
                using pointer = typename value_container_type::pointer;
                using const_pointer = typename value_container_type::const_pointer;
                using const_iterator = typename value_container_type::const_iterator;
                using iterator = std::conditional_t<is_map_v<T>, typename value_container_type::iterator, const_iterator>;
                using bucket_type = Bucket;

            private:
                using value_idx_type = decltype(Bucket::m_value_idx);
                using dist_and_fingerprint_type = decltype(Bucket::m_dist_and_fingerprint);

                static_assert(std::is_trivially_destructible_v<Bucket>, "assert there's no need to call destructor / std::destroy");
                static_assert(std::is_trivially_copyable_v<Bucket>, "assert we can just memset / memcpy");

                value_container_type m_values{}; // Contains all the key-value pairs in one densely stored container. No holes.
                using bucket_pointer = typename std::allocator_traits<bucket_alloc>::pointer;
                bucket_pointer m_buckets{};
                size_t m_num_buckets = 0;
                size_t m_max_bucket_capacity = 0;
                float m_max_load_factor = default_max_load_factor;
                Hash m_hash{};
                KeyEqual m_equal{};
                uint8_t m_shifts = initial_shifts;

                [[nodiscard]] auto next(value_idx_type bucket_idx) const -> value_idx_type
                {
                    return ANKERL_UNORDERED_DENSE_UNLIKELY(bucket_idx + 1U == m_num_buckets)
                               ? 0
                               : static_cast<value_idx_type>(bucket_idx + 1U);
                }

                // Helper to access bucket through pointer types
                [[nodiscard]] static constexpr auto at(bucket_pointer bucket_ptr, size_t offset) -> Bucket &
                {
                    return *(bucket_ptr + static_cast<typename std::allocator_traits<bucket_alloc>::difference_type>(offset));
                }

                // use the dist_inc and dist_dec functions so that uint16_t types work without warning
                [[nodiscard]] static constexpr auto dist_inc(dist_and_fingerprint_type x) -> dist_and_fingerprint_type
                {
                    return static_cast<dist_and_fingerprint_type>(x + Bucket::dist_inc);
                }

                [[nodiscard]] static constexpr auto dist_dec(dist_and_fingerprint_type x) -> dist_and_fingerprint_type
                {
                    return static_cast<dist_and_fingerprint_type>(x - Bucket::dist_inc);
                }

                // The goal of mixed_hash is to always produce a high quality 64bit hash.
                template <typename K>
                [[nodiscard]] constexpr auto mixed_hash(K const &key) const -> uint64_t
                {
                    if constexpr (is_detected_v<detect_avalanching, Hash>)
                    {
                        // we know that the hash is good because is_avalanching.
                        if constexpr (sizeof(decltype(m_hash(key))) < sizeof(uint64_t))
                        {
                            // 32bit hash and is_avalanching => multiply with a constant to avalanche bits upwards
                            return m_hash(key) * UINT64_C(0x9ddfea08eb382d69);
                        }
                        else
                        {
                            // 64bit and is_avalanching => only use the hash itself.
                            return m_hash(key);
                        }
                    }
                    else
                    {
                        // not is_avalanching => apply wyhash
                        return wyhash::hash(m_hash(key));
                    }
                }

                [[nodiscard]] constexpr auto dist_and_fingerprint_from_hash(uint64_t hash) const -> dist_and_fingerprint_type
                {
                    return Bucket::dist_inc | (static_cast<dist_and_fingerprint_type>(hash) & Bucket::fingerprint_mask);
                }

                [[nodiscard]] constexpr auto bucket_idx_from_hash(uint64_t hash) const -> value_idx_type
                {
                    return static_cast<value_idx_type>(hash >> m_shifts);
                }

                [[nodiscard]] static constexpr auto get_key(value_type const &vt) -> key_type const &
                {
                    if constexpr (is_map_v<T>)
                    {
                        return vt.first;
                    }
                    else
                    {
                        return vt;
                    }
                }

                template <typename K>
                [[nodiscard]] auto next_while_less(K const &key) const -> Bucket
                {
                    auto hash = mixed_hash(key);
                    auto dist_and_fingerprint = dist_and_fingerprint_from_hash(hash);
                    auto bucket_idx = bucket_idx_from_hash(hash);

                    while (dist_and_fingerprint < at(m_buckets, bucket_idx).m_dist_and_fingerprint)
                    {
                        dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                        bucket_idx = next(bucket_idx);
                    }
                    return {dist_and_fingerprint, bucket_idx};
                }

                void place_and_shift_up(Bucket bucket, value_idx_type place)
                {
                    while (0 != at(m_buckets, place).m_dist_and_fingerprint)
                    {
                        bucket = std::exchange(at(m_buckets, place), bucket);
                        bucket.m_dist_and_fingerprint = dist_inc(bucket.m_dist_and_fingerprint);
                        place = next(place);
                    }
                    at(m_buckets, place) = bucket;
                }

                [[nodiscard]] static constexpr auto calc_num_buckets(uint8_t shifts) -> size_t
                {
                    return (std::min)(max_bucket_count(), size_t{1} << (64U - shifts));
                }

                [[nodiscard]] constexpr auto calc_shifts_for_size(size_t s) const -> uint8_t
                {
                    auto shifts = initial_shifts;
                    while (shifts > 0 && static_cast<size_t>(static_cast<float>(calc_num_buckets(shifts)) * max_load_factor()) < s)
                    {
                        --shifts;
                    }
                    return shifts;
                }

                // assumes m_values has data, m_buckets=m_buckets_end=nullptr, m_shifts is INITIAL_SHIFTS
                void copy_buckets(table const &other)
                {
                    if (!empty())
                    {
                        m_shifts = other.m_shifts;
                        allocate_buckets_from_shift();
                        std::memcpy(m_buckets, other.m_buckets, sizeof(Bucket) * bucket_count());
                    }
                }

                /**
                 * True when no element can be added any more without increasing the size
                 */
                [[nodiscard]] auto is_full() const -> bool
                {
                    return size() >= m_max_bucket_capacity;
                }

                void deallocate_buckets()
                {
                    auto ba = bucket_alloc(m_values.get_allocator());
                    if (nullptr != m_buckets)
                    {
                        bucket_alloc_traits::deallocate(ba, m_buckets, bucket_count());
                        m_buckets = nullptr;
                    }
                    m_num_buckets = 0;
                    m_max_bucket_capacity = 0;
                }

                void allocate_buckets_from_shift()
                {
                    auto ba = bucket_alloc(m_values.get_allocator());
                    m_num_buckets = calc_num_buckets(m_shifts);
                    m_buckets = bucket_alloc_traits::allocate(ba, m_num_buckets);
                    if (m_num_buckets == max_bucket_count())
                    {
                        // reached the maximum, make sure we can use each bucket
                        m_max_bucket_capacity = max_bucket_count();
                    }
                    else
                    {
                        m_max_bucket_capacity = static_cast<value_idx_type>(static_cast<float>(m_num_buckets) * max_load_factor());
                    }
                }

                void clear_buckets()
                {
                    if (m_buckets != nullptr)
                    {
                        std::memset(&*m_buckets, 0, sizeof(Bucket) * bucket_count());
                    }
                }

                void clear_and_fill_buckets_from_values()
                {
                    clear_buckets();
                    for (value_idx_type value_idx = 0, end_idx = static_cast<value_idx_type>(m_values.size()); value_idx < end_idx;
                         ++value_idx)
                    {
                        auto const &key = get_key(m_values[value_idx]);
                        auto [dist_and_fingerprint, bucket] = next_while_less(key);

                        // we know for certain that key has not yet been inserted, so no need to check it.
                        place_and_shift_up({dist_and_fingerprint, value_idx}, bucket);
                    }
                }

                void increase_size()
                {
                    if (ANKERL_UNORDERED_DENSE_UNLIKELY(m_max_bucket_capacity == max_bucket_count()))
                    {
                        on_error_bucket_overflow();
                    }
                    --m_shifts;
                    deallocate_buckets();
                    allocate_buckets_from_shift();
                    clear_and_fill_buckets_from_values();
                }

                void do_erase(value_idx_type bucket_idx)
                {
                    auto const value_idx_to_remove = at(m_buckets, bucket_idx).m_value_idx;

                    // shift down until either empty or an element with correct spot is found
                    auto next_bucket_idx = next(bucket_idx);
                    while (at(m_buckets, next_bucket_idx).m_dist_and_fingerprint >= Bucket::dist_inc * 2)
                    {
                        at(m_buckets, bucket_idx) = {dist_dec(at(m_buckets, next_bucket_idx).m_dist_and_fingerprint),
                                                     at(m_buckets, next_bucket_idx).m_value_idx};
                        bucket_idx = std::exchange(next_bucket_idx, next(next_bucket_idx));
                    }
                    at(m_buckets, bucket_idx) = {};

                    // update m_values
                    if (value_idx_to_remove != m_values.size() - 1)
                    {
                        // no luck, we'll have to replace the value with the last one and update the index accordingly
                        auto &val = m_values[value_idx_to_remove];
                        val = std::move(m_values.back());

                        // update the values_idx of the moved entry. No need to play the info game, just look until we find the values_idx
                        auto mh = mixed_hash(get_key(val));
                        bucket_idx = bucket_idx_from_hash(mh);

                        auto const values_idx_back = static_cast<value_idx_type>(m_values.size() - 1);
                        while (values_idx_back != at(m_buckets, bucket_idx).m_value_idx)
                        {
                            bucket_idx = next(bucket_idx);
                        }
                        at(m_buckets, bucket_idx).m_value_idx = value_idx_to_remove;
                    }
                    m_values.pop_back();
                }

                template <typename K>
                auto do_erase_key(K &&key) -> size_t
                {
                    if (empty())
                    {
                        return 0;
                    }

                    auto [dist_and_fingerprint, bucket_idx] = next_while_less(key);

                    while (dist_and_fingerprint == at(m_buckets, bucket_idx).m_dist_and_fingerprint &&
                           !m_equal(key, get_key(m_values[at(m_buckets, bucket_idx).m_value_idx])))
                    {
                        dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                        bucket_idx = next(bucket_idx);
                    }

                    if (dist_and_fingerprint != at(m_buckets, bucket_idx).m_dist_and_fingerprint)
                    {
                        return 0;
                    }
                    do_erase(bucket_idx);
                    return 1;
                }

                template <class K, class M>
                auto do_insert_or_assign(K &&key, M &&mapped) -> std::pair<iterator, bool>
                {
                    auto it_isinserted = try_emplace(std::forward<K>(key), std::forward<M>(mapped));
                    if (!it_isinserted.second)
                    {
                        it_isinserted.first->second = std::forward<M>(mapped);
                    }
                    return it_isinserted;
                }

                template <typename K, typename... Args>
                auto do_place_element(dist_and_fingerprint_type dist_and_fingerprint, value_idx_type bucket_idx, K &&key, Args &&...args)
                    -> std::pair<iterator, bool>
                {

                    // emplace the new value. If that throws an exception, no harm done; index is still in a valid state
                    m_values.emplace_back(std::piecewise_construct,
                                          std::forward_as_tuple(std::forward<K>(key)),
                                          std::forward_as_tuple(std::forward<Args>(args)...));

                    // place element and shift up until we find an empty spot
                    auto value_idx = static_cast<value_idx_type>(m_values.size() - 1);
                    place_and_shift_up({dist_and_fingerprint, value_idx}, bucket_idx);
                    return {begin() + static_cast<difference_type>(value_idx), true};
                }

                template <typename K, typename... Args>
                auto do_try_emplace(K &&key, Args &&...args) -> std::pair<iterator, bool>
                {
                    if (ANKERL_UNORDERED_DENSE_UNLIKELY(is_full()))
                    {
                        increase_size();
                    }

                    auto hash = mixed_hash(key);
                    auto dist_and_fingerprint = dist_and_fingerprint_from_hash(hash);
                    auto bucket_idx = bucket_idx_from_hash(hash);

                    while (true)
                    {
                        auto *bucket = &at(m_buckets, bucket_idx);
                        if (dist_and_fingerprint == bucket->m_dist_and_fingerprint)
                        {
                            if (m_equal(key, get_key(m_values[bucket->m_value_idx])))
                            {
                                return {begin() + static_cast<difference_type>(bucket->m_value_idx), false};
                            }
                        }
                        else if (dist_and_fingerprint > bucket->m_dist_and_fingerprint)
                        {
                            return do_place_element(dist_and_fingerprint, bucket_idx, std::forward<K>(key), std::forward<Args>(args)...);
                        }
                        dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                        bucket_idx = next(bucket_idx);
                    }
                }

                template <typename K>
                auto do_find(K const &key) -> iterator
                {
                    if (ANKERL_UNORDERED_DENSE_UNLIKELY(empty()))
                    {
                        return end();
                    }

                    auto mh = mixed_hash(key);
                    auto dist_and_fingerprint = dist_and_fingerprint_from_hash(mh);
                    auto bucket_idx = bucket_idx_from_hash(mh);
                    auto *bucket = &at(m_buckets, bucket_idx);

                    // unrolled loop. *Always* check a few directly, then enter the loop. This is faster.
                    if (dist_and_fingerprint == bucket->m_dist_and_fingerprint && m_equal(key, get_key(m_values[bucket->m_value_idx])))
                    {
                        return begin() + static_cast<difference_type>(bucket->m_value_idx);
                    }
                    dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                    bucket_idx = next(bucket_idx);
                    bucket = &at(m_buckets, bucket_idx);

                    if (dist_and_fingerprint == bucket->m_dist_and_fingerprint && m_equal(key, get_key(m_values[bucket->m_value_idx])))
                    {
                        return begin() + static_cast<difference_type>(bucket->m_value_idx);
                    }
                    dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                    bucket_idx = next(bucket_idx);
                    bucket = &at(m_buckets, bucket_idx);

                    while (true)
                    {
                        if (dist_and_fingerprint == bucket->m_dist_and_fingerprint)
                        {
                            if (m_equal(key, get_key(m_values[bucket->m_value_idx])))
                            {
                                return begin() + static_cast<difference_type>(bucket->m_value_idx);
                            }
                        }
                        else if (dist_and_fingerprint > bucket->m_dist_and_fingerprint)
                        {
                            return end();
                        }
                        dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                        bucket_idx = next(bucket_idx);
                        bucket = &at(m_buckets, bucket_idx);
                    }
                }

                template <typename K>
                auto do_find(K const &key) const -> const_iterator
                {
                    return const_cast<table *>(this)->do_find(key); // NOLINT(cppcoreguidelines-pro-type-const-cast)
                }

                template <typename K, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto do_at(K const &key) -> Q &
                {
                    if (auto it = find(key); ANKERL_UNORDERED_DENSE_LIKELY(end() != it))
                    {
                        return it->second;
                    }
                    on_error_key_not_found();
                }

                template <typename K, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto do_at(K const &key) const -> Q const &
                {
                    return const_cast<table *>(this)->at(key); // NOLINT(cppcoreguidelines-pro-type-const-cast)
                }

            public:
                table()
                    : table(0) {}

                explicit table(size_t bucket_count,
                               Hash const &hash = Hash(),
                               KeyEqual const &equal = KeyEqual(),
                               allocator_type const &alloc_or_container = allocator_type())
                    : m_values(alloc_or_container), m_hash(hash), m_equal(equal)
                {
                    if (0 != bucket_count)
                    {
                        reserve(bucket_count);
                    }
                }

                table(size_t bucket_count, allocator_type const &alloc)
                    : table(bucket_count, Hash(), KeyEqual(), alloc) {}

                table(size_t bucket_count, Hash const &hash, allocator_type const &alloc)
                    : table(bucket_count, hash, KeyEqual(), alloc) {}

                explicit table(allocator_type const &alloc)
                    : table(0, Hash(), KeyEqual(), alloc) {}

                template <class InputIt>
                table(InputIt first,
                      InputIt last,
                      size_type bucket_count = 0,
                      Hash const &hash = Hash(),
                      KeyEqual const &equal = KeyEqual(),
                      allocator_type const &alloc = allocator_type())
                    : table(bucket_count, hash, equal, alloc)
                {
                    insert(first, last);
                }

                template <class InputIt>
                table(InputIt first, InputIt last, size_type bucket_count, allocator_type const &alloc)
                    : table(first, last, bucket_count, Hash(), KeyEqual(), alloc) {}

                template <class InputIt>
                table(InputIt first, InputIt last, size_type bucket_count, Hash const &hash, allocator_type const &alloc)
                    : table(first, last, bucket_count, hash, KeyEqual(), alloc) {}

                table(table const &other)
                    : table(other, other.m_values.get_allocator()) {}

                table(table const &other, allocator_type const &alloc)
                    : m_values(other.m_values, alloc), m_max_load_factor(other.m_max_load_factor), m_hash(other.m_hash), m_equal(other.m_equal)
                {
                    copy_buckets(other);
                }

                table(table &&other) noexcept
                    : table(std::move(other), other.m_values.get_allocator()) {}

                table(table &&other, allocator_type const &alloc) noexcept
                    : m_values(alloc)
                {
                    *this = std::move(other);
                }

                table(std::initializer_list<value_type> ilist,
                      size_t bucket_count = 0,
                      Hash const &hash = Hash(),
                      KeyEqual const &equal = KeyEqual(),
                      allocator_type const &alloc = allocator_type())
                    : table(bucket_count, hash, equal, alloc)
                {
                    insert(ilist);
                }

                table(std::initializer_list<value_type> ilist, size_type bucket_count, allocator_type const &alloc)
                    : table(ilist, bucket_count, Hash(), KeyEqual(), alloc) {}

                table(std::initializer_list<value_type> init, size_type bucket_count, Hash const &hash, allocator_type const &alloc)
                    : table(init, bucket_count, hash, KeyEqual(), alloc) {}

                ~table()
                {
                    if (nullptr != m_buckets)
                    {
                        auto ba = bucket_alloc(m_values.get_allocator());
                        bucket_alloc_traits::deallocate(ba, m_buckets, bucket_count());
                    }
                }

                auto operator=(table const &other) -> table &
                {
                    if (&other != this)
                    {
                        deallocate_buckets(); // deallocate before m_values is set (might have another allocator)
                        m_values = other.m_values;
                        m_max_load_factor = other.m_max_load_factor;
                        m_hash = other.m_hash;
                        m_equal = other.m_equal;
                        m_shifts = initial_shifts;
                        copy_buckets(other);
                    }
                    return *this;
                }

                auto operator=(table &&other) noexcept(
                    noexcept(std::is_nothrow_move_assignable_v<value_container_type> && std::is_nothrow_move_assignable_v<Hash> &&
                             std::is_nothrow_move_assignable_v<KeyEqual>)) -> table &
                {
                    if (&other != this)
                    {
                        deallocate_buckets(); // deallocate before m_values is set (might have another allocator)
                        m_values = std::move(other.m_values);
                        other.m_values.clear();

                        // we can only reuse m_buckets when both maps have the same allocator!
                        if (get_allocator() == other.get_allocator())
                        {
                            m_buckets = std::exchange(other.m_buckets, nullptr);
                            m_num_buckets = std::exchange(other.m_num_buckets, 0);
                            m_max_bucket_capacity = std::exchange(other.m_max_bucket_capacity, 0);
                            m_shifts = std::exchange(other.m_shifts, initial_shifts);
                            m_max_load_factor = std::exchange(other.m_max_load_factor, default_max_load_factor);
                            m_hash = std::exchange(other.m_hash, {});
                            m_equal = std::exchange(other.m_equal, {});
                        }
                        else
                        {
                            // set max_load_factor *before* copying the other's buckets, so we have the same
                            // behavior
                            m_max_load_factor = other.m_max_load_factor;

                            // copy_buckets sets m_buckets, m_num_buckets, m_max_bucket_capacity, m_shifts
                            copy_buckets(other);
                            // clear's the other's buckets so other is now already usable.
                            other.clear_buckets();
                            m_hash = other.m_hash;
                            m_equal = other.m_equal;
                        }
                        // map "other" is now already usable, it's empty.
                    }
                    return *this;
                }

                auto operator=(std::initializer_list<value_type> ilist) -> table &
                {
                    clear();
                    insert(ilist);
                    return *this;
                }

                auto get_allocator() const noexcept -> allocator_type
                {
                    return m_values.get_allocator();
                }

                // iterators //////////////////////////////////////////////////////////////

                auto begin() noexcept -> iterator
                {
                    return m_values.begin();
                }

                auto begin() const noexcept -> const_iterator
                {
                    return m_values.begin();
                }

                auto cbegin() const noexcept -> const_iterator
                {
                    return m_values.cbegin();
                }

                auto end() noexcept -> iterator
                {
                    return m_values.end();
                }

                auto cend() const noexcept -> const_iterator
                {
                    return m_values.cend();
                }

                auto end() const noexcept -> const_iterator
                {
                    return m_values.end();
                }

                // capacity ///////////////////////////////////////////////////////////////

                [[nodiscard]] auto empty() const noexcept -> bool
                {
                    return m_values.empty();
                }

                [[nodiscard]] auto size() const noexcept -> size_t
                {
                    return m_values.size();
                }

                [[nodiscard]] static constexpr auto max_size() noexcept -> size_t
                {
                    if constexpr ((std::numeric_limits<value_idx_type>::max)() == (std::numeric_limits<size_t>::max)())
                    {
                        return size_t{1} << (sizeof(value_idx_type) * 8 - 1);
                    }
                    else
                    {
                        return size_t{1} << (sizeof(value_idx_type) * 8);
                    }
                }

                // modifiers //////////////////////////////////////////////////////////////

                void clear()
                {
                    m_values.clear();
                    clear_buckets();
                }

                auto insert(value_type const &value) -> std::pair<iterator, bool>
                {
                    return emplace(value);
                }

                auto insert(value_type &&value) -> std::pair<iterator, bool>
                {
                    return emplace(std::move(value));
                }

                template <class P, std::enable_if_t<std::is_constructible_v<value_type, P &&>, bool> = true>
                auto insert(P &&value) -> std::pair<iterator, bool>
                {
                    return emplace(std::forward<P>(value));
                }

                auto insert(const_iterator /*hint*/, value_type const &value) -> iterator
                {
                    return insert(value).first;
                }

                auto insert(const_iterator /*hint*/, value_type &&value) -> iterator
                {
                    return insert(std::move(value)).first;
                }

                template <class P, std::enable_if_t<std::is_constructible_v<value_type, P &&>, bool> = true>
                auto insert(const_iterator /*hint*/, P &&value) -> iterator
                {
                    return insert(std::forward<P>(value)).first;
                }

                template <class InputIt>
                void insert(InputIt first, InputIt last)
                {
                    while (first != last)
                    {
                        insert(*first);
                        ++first;
                    }
                }

                void insert(std::initializer_list<value_type> ilist)
                {
                    insert(ilist.begin(), ilist.end());
                }

                // nonstandard API: *this is emptied.
                // Also see "A Standard flat_map" https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p0429r9.pdf
                auto extract() && -> value_container_type
                {
                    return std::move(m_values);
                }

                // nonstandard API:
                // Discards the internally held container and replaces it with the one passed. Erases non-unique elements.
                auto replace(value_container_type &&container)
                {
                    if (ANKERL_UNORDERED_DENSE_UNLIKELY(container.size() > max_size()))
                    {
                        on_error_too_many_elements();
                    }
                    auto shifts = calc_shifts_for_size(container.size());
                    if (0 == m_num_buckets || shifts < m_shifts || container.get_allocator() != m_values.get_allocator())
                    {
                        m_shifts = shifts;
                        deallocate_buckets();
                        allocate_buckets_from_shift();
                    }
                    clear_buckets();

                    m_values = std::move(container);

                    // can't use clear_and_fill_buckets_from_values() because container elements might not be unique
                    auto value_idx = value_idx_type{};

                    // loop until we reach the end of the container. duplicated entries will be replaced with back().
                    while (value_idx != static_cast<value_idx_type>(m_values.size()))
                    {
                        auto const &key = get_key(m_values[value_idx]);

                        auto hash = mixed_hash(key);
                        auto dist_and_fingerprint = dist_and_fingerprint_from_hash(hash);
                        auto bucket_idx = bucket_idx_from_hash(hash);

                        bool key_found = false;
                        while (true)
                        {
                            auto const &bucket = at(m_buckets, bucket_idx);
                            if (dist_and_fingerprint > bucket.m_dist_and_fingerprint)
                            {
                                break;
                            }
                            if (dist_and_fingerprint == bucket.m_dist_and_fingerprint &&
                                m_equal(key, get_key(m_values[bucket.m_value_idx])))
                            {
                                key_found = true;
                                break;
                            }
                            dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                            bucket_idx = next(bucket_idx);
                        }

                        if (key_found)
                        {
                            if (value_idx != static_cast<value_idx_type>(m_values.size() - 1))
                            {
                                m_values[value_idx] = std::move(m_values.back());
                            }
                            m_values.pop_back();
                        }
                        else
                        {
                            place_and_shift_up({dist_and_fingerprint, value_idx}, bucket_idx);
                            ++value_idx;
                        }
                    }
                }

                template <class M, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto insert_or_assign(Key const &key, M &&mapped) -> std::pair<iterator, bool>
                {
                    return do_insert_or_assign(key, std::forward<M>(mapped));
                }

                template <class M, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto insert_or_assign(Key &&key, M &&mapped) -> std::pair<iterator, bool>
                {
                    return do_insert_or_assign(std::move(key), std::forward<M>(mapped));
                }

                template <typename K,
                          typename M,
                          typename Q = T,
                          typename H = Hash,
                          typename KE = KeyEqual,
                          std::enable_if_t<is_map_v<Q> && is_transparent_v<H, KE>, bool> = true>
                auto insert_or_assign(K &&key, M &&mapped) -> std::pair<iterator, bool>
                {
                    return do_insert_or_assign(std::forward<K>(key), std::forward<M>(mapped));
                }

                template <class M, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto insert_or_assign(const_iterator /*hint*/, Key const &key, M &&mapped) -> iterator
                {
                    return do_insert_or_assign(key, std::forward<M>(mapped)).first;
                }

                template <class M, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto insert_or_assign(const_iterator /*hint*/, Key &&key, M &&mapped) -> iterator
                {
                    return do_insert_or_assign(std::move(key), std::forward<M>(mapped)).first;
                }

                template <typename K,
                          typename M,
                          typename Q = T,
                          typename H = Hash,
                          typename KE = KeyEqual,
                          std::enable_if_t<is_map_v<Q> && is_transparent_v<H, KE>, bool> = true>
                auto insert_or_assign(const_iterator /*hint*/, K &&key, M &&mapped) -> iterator
                {
                    return do_insert_or_assign(std::forward<K>(key), std::forward<M>(mapped)).first;
                }

                // Single arguments for unordered_set can be used without having to construct the value_type
                template <class K,
                          typename Q = T,
                          typename H = Hash,
                          typename KE = KeyEqual,
                          std::enable_if_t<!is_map_v<Q> && is_transparent_v<H, KE>, bool> = true>
                auto emplace(K &&key) -> std::pair<iterator, bool>
                {
                    if (is_full())
                    {
                        increase_size();
                    }

                    auto hash = mixed_hash(key);
                    auto dist_and_fingerprint = dist_and_fingerprint_from_hash(hash);
                    auto bucket_idx = bucket_idx_from_hash(hash);

                    while (dist_and_fingerprint <= at(m_buckets, bucket_idx).m_dist_and_fingerprint)
                    {
                        if (dist_and_fingerprint == at(m_buckets, bucket_idx).m_dist_and_fingerprint &&
                            m_equal(key, m_values[at(m_buckets, bucket_idx).m_value_idx]))
                        {
                            // found it, return without ever actually creating anything
                            return {begin() + static_cast<difference_type>(at(m_buckets, bucket_idx).m_value_idx), false};
                        }
                        dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                        bucket_idx = next(bucket_idx);
                    }

                    // value is new, insert element first, so when exception happens we are in a valid state
                    m_values.emplace_back(std::forward<K>(key));
                    // now place the bucket and shift up until we find an empty spot
                    auto value_idx = static_cast<value_idx_type>(m_values.size() - 1);
                    place_and_shift_up({dist_and_fingerprint, value_idx}, bucket_idx);
                    return {begin() + static_cast<difference_type>(value_idx), true};
                }

                template <class... Args>
                auto emplace(Args &&...args) -> std::pair<iterator, bool>
                {
                    if (is_full())
                    {
                        increase_size();
                    }

                    // we have to instantiate the value_type to be able to access the key.
                    // 1. emplace_back the object so it is constructed. 2. If the key is already there, pop it later in the loop.
                    auto &key = get_key(m_values.emplace_back(std::forward<Args>(args)...));
                    auto hash = mixed_hash(key);
                    auto dist_and_fingerprint = dist_and_fingerprint_from_hash(hash);
                    auto bucket_idx = bucket_idx_from_hash(hash);

                    while (dist_and_fingerprint <= at(m_buckets, bucket_idx).m_dist_and_fingerprint)
                    {
                        if (dist_and_fingerprint == at(m_buckets, bucket_idx).m_dist_and_fingerprint &&
                            m_equal(key, get_key(m_values[at(m_buckets, bucket_idx).m_value_idx])))
                        {
                            m_values.pop_back(); // value was already there, so get rid of it
                            return {begin() + static_cast<difference_type>(at(m_buckets, bucket_idx).m_value_idx), false};
                        }
                        dist_and_fingerprint = dist_inc(dist_and_fingerprint);
                        bucket_idx = next(bucket_idx);
                    }

                    // value is new, place the bucket and shift up until we find an empty spot
                    auto value_idx = static_cast<value_idx_type>(m_values.size() - 1);
                    place_and_shift_up({dist_and_fingerprint, value_idx}, bucket_idx);

                    return {begin() + static_cast<difference_type>(value_idx), true};
                }

                template <class... Args>
                auto emplace_hint(const_iterator /*hint*/, Args &&...args) -> iterator
                {
                    return emplace(std::forward<Args>(args)...).first;
                }

                template <class... Args, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto try_emplace(Key const &key, Args &&...args) -> std::pair<iterator, bool>
                {
                    return do_try_emplace(key, std::forward<Args>(args)...);
                }

                template <class... Args, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto try_emplace(Key &&key, Args &&...args) -> std::pair<iterator, bool>
                {
                    return do_try_emplace(std::move(key), std::forward<Args>(args)...);
                }

                template <class... Args, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto try_emplace(const_iterator /*hint*/, Key const &key, Args &&...args) -> iterator
                {
                    return do_try_emplace(key, std::forward<Args>(args)...).first;
                }

                template <class... Args, typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto try_emplace(const_iterator /*hint*/, Key &&key, Args &&...args) -> iterator
                {
                    return do_try_emplace(std::move(key), std::forward<Args>(args)...).first;
                }

                template <
                    typename K,
                    typename... Args,
                    typename Q = T,
                    typename H = Hash,
                    typename KE = KeyEqual,
                    std::enable_if_t<is_map_v<Q> && is_transparent_v<H, KE> && is_neither_convertible_v<K &&, iterator, const_iterator>,
                                     bool> = true>
                auto try_emplace(K &&key, Args &&...args) -> std::pair<iterator, bool>
                {
                    return do_try_emplace(std::forward<K>(key), std::forward<Args>(args)...);
                }

                template <
                    typename K,
                    typename... Args,
                    typename Q = T,
                    typename H = Hash,
                    typename KE = KeyEqual,
                    std::enable_if_t<is_map_v<Q> && is_transparent_v<H, KE> && is_neither_convertible_v<K &&, iterator, const_iterator>,
                                     bool> = true>
                auto try_emplace(const_iterator /*hint*/, K &&key, Args &&...args) -> iterator
                {
                    return do_try_emplace(std::forward<K>(key), std::forward<Args>(args)...).first;
                }

                auto erase(iterator it) -> iterator
                {
                    auto hash = mixed_hash(get_key(*it));
                    auto bucket_idx = bucket_idx_from_hash(hash);

                    auto const value_idx_to_remove = static_cast<value_idx_type>(it - cbegin());
                    while (at(m_buckets, bucket_idx).m_value_idx != value_idx_to_remove)
                    {
                        bucket_idx = next(bucket_idx);
                    }

                    do_erase(bucket_idx);
                    return begin() + static_cast<difference_type>(value_idx_to_remove);
                }

                template <typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto erase(const_iterator it) -> iterator
                {
                    return erase(begin() + (it - cbegin()));
                }

                auto erase(const_iterator first, const_iterator last) -> iterator
                {
                    auto const idx_first = first - cbegin();
                    auto const idx_last = last - cbegin();
                    auto const first_to_last = std::distance(first, last);
                    auto const last_to_end = std::distance(last, cend());

                    // remove elements from left to right which moves elements from the end back
                    auto const mid = idx_first + (std::min)(first_to_last, last_to_end);
                    auto idx = idx_first;
                    while (idx != mid)
                    {
                        erase(begin() + idx);
                        ++idx;
                    }

                    // all elements from the right are moved, now remove the last element until all done
                    idx = idx_last;
                    while (idx != mid)
                    {
                        --idx;
                        erase(begin() + idx);
                    }

                    return begin() + idx_first;
                }

                auto erase(Key const &key) -> size_t
                {
                    return do_erase_key(key);
                }

                template <class K, class H = Hash, class KE = KeyEqual, std::enable_if_t<is_transparent_v<H, KE>, bool> = true>
                auto erase(K &&key) -> size_t
                {
                    return do_erase_key(std::forward<K>(key));
                }

                void swap(table &other) noexcept(noexcept(std::is_nothrow_swappable_v<value_container_type> &&
                                                          std::is_nothrow_swappable_v<Hash> && std::is_nothrow_swappable_v<KeyEqual>))
                {
                    using std::swap;
                    swap(other, *this);
                }

                // lookup /////////////////////////////////////////////////////////////////

                template <typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto at(key_type const &key) -> Q &
                {
                    return do_at(key);
                }

                template <typename K,
                          typename Q = T,
                          typename H = Hash,
                          typename KE = KeyEqual,
                          std::enable_if_t<is_map_v<Q> && is_transparent_v<H, KE>, bool> = true>
                auto at(K const &key) -> Q &
                {
                    return do_at(key);
                }

                template <typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto at(key_type const &key) const -> Q const &
                {
                    return do_at(key);
                }

                template <typename K,
                          typename Q = T,
                          typename H = Hash,
                          typename KE = KeyEqual,
                          std::enable_if_t<is_map_v<Q> && is_transparent_v<H, KE>, bool> = true>
                auto at(K const &key) const -> Q const &
                {
                    return do_at(key);
                }

                template <typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto operator[](Key const &key) -> Q &
                {
                    return try_emplace(key).first->second;
                }

                template <typename Q = T, std::enable_if_t<is_map_v<Q>, bool> = true>
                auto operator[](Key &&key) -> Q &
                {
                    return try_emplace(std::move(key)).first->second;
                }

                template <typename K,
                          typename Q = T,
                          typename H = Hash,
                          typename KE = KeyEqual,
                          std::enable_if_t<is_map_v<Q> && is_transparent_v<H, KE>, bool> = true>
                auto operator[](K &&key) -> Q &
                {
                    return try_emplace(std::forward<K>(key)).first->second;
                }

                auto count(Key const &key) const -> size_t
                {
                    return find(key) == end() ? 0 : 1;
                }

                template <class K, class H = Hash, class KE = KeyEqual, std::enable_if_t<is_transparent_v<H, KE>, bool> = true>
                auto count(K const &key) const -> size_t
                {
                    return find(key) == end() ? 0 : 1;
                }

                auto find(Key const &key) -> iterator
                {
                    return do_find(key);
                }

                auto find(Key const &key) const -> const_iterator
                {
                    return do_find(key);
                }

                template <class K, class H = Hash, class KE = KeyEqual, std::enable_if_t<is_transparent_v<H, KE>, bool> = true>
                auto find(K const &key) -> iterator
                {
                    return do_find(key);
                }

                template <class K, class H = Hash, class KE = KeyEqual, std::enable_if_t<is_transparent_v<H, KE>, bool> = true>
                auto find(K const &key) const -> const_iterator
                {
                    return do_find(key);
                }

                auto contains(Key const &key) const -> bool
                {
                    return find(key) != end();
                }

                template <class K, class H = Hash, class KE = KeyEqual, std::enable_if_t<is_transparent_v<H, KE>, bool> = true>
                auto contains(K const &key) const -> bool
                {
                    return find(key) != end();
                }

                auto equal_range(Key const &key) -> std::pair<iterator, iterator>
                {
                    auto it = do_find(key);
                    return {it, it == end() ? end() : it + 1};
                }

                auto equal_range(const Key &key) const -> std::pair<const_iterator, const_iterator>
                {
                    auto it = do_find(key);
                    return {it, it == end() ? end() : it + 1};
                }

                template <class K, class H = Hash, class KE = KeyEqual, std::enable_if_t<is_transparent_v<H, KE>, bool> = true>
                auto equal_range(K const &key) -> std::pair<iterator, iterator>
                {
                    auto it = do_find(key);
                    return {it, it == end() ? end() : it + 1};
                }

                template <class K, class H = Hash, class KE = KeyEqual, std::enable_if_t<is_transparent_v<H, KE>, bool> = true>
                auto equal_range(K const &key) const -> std::pair<const_iterator, const_iterator>
                {
                    auto it = do_find(key);
                    return {it, it == end() ? end() : it + 1};
                }

                // bucket interface ///////////////////////////////////////////////////////

                auto bucket_count() const noexcept -> size_t
                { // NOLINT(modernize-use-nodiscard)
                    return m_num_buckets;
                }

                static constexpr auto max_bucket_count() noexcept -> size_t
                { // NOLINT(modernize-use-nodiscard)
                    return max_size();
                }

                // hash policy ////////////////////////////////////////////////////////////

                [[nodiscard]] auto load_factor() const -> float
                {
                    return bucket_count() ? static_cast<float>(size()) / static_cast<float>(bucket_count()) : 0.0F;
                }

                [[nodiscard]] auto max_load_factor() const -> float
                {
                    return m_max_load_factor;
                }

                void max_load_factor(float ml)
                {
                    m_max_load_factor = ml;
                    if (m_num_buckets != max_bucket_count())
                    {
                        m_max_bucket_capacity = static_cast<value_idx_type>(static_cast<float>(bucket_count()) * max_load_factor());
                    }
                }

                void rehash(size_t count)
                {
                    count = (std::min)(count, max_size());
                    auto shifts = calc_shifts_for_size((std::max)(count, size()));
                    if (shifts != m_shifts)
                    {
                        m_shifts = shifts;
                        deallocate_buckets();
                        m_values.shrink_to_fit();
                        allocate_buckets_from_shift();
                        clear_and_fill_buckets_from_values();
                    }
                }

                void reserve(size_t capa)
                {
                    capa = (std::min)(capa, max_size());
                    if constexpr (has_reserve<value_container_type>)
                    {
                        // std::deque doesn't have reserve(). Make sure we only call when available
                        m_values.reserve(capa);
                    }
                    auto shifts = calc_shifts_for_size((std::max)(capa, size()));
                    if (0 == m_num_buckets || shifts < m_shifts)
                    {
                        m_shifts = shifts;
                        deallocate_buckets();
                        allocate_buckets_from_shift();
                        clear_and_fill_buckets_from_values();
                    }
                }

                // observers //////////////////////////////////////////////////////////////

                auto hash_function() const -> hasher
                {
                    return m_hash;
                }

                auto key_eq() const -> key_equal
                {
                    return m_equal;
                }

                // nonstandard API: expose the underlying values container
                [[nodiscard]] auto values() const noexcept -> value_container_type const &
                {
                    return m_values;
                }

                // non-member functions ///////////////////////////////////////////////////

                friend auto operator==(table const &a, table const &b) -> bool
                {
                    if (&a == &b)
                    {
                        return true;
                    }
                    if (a.size() != b.size())
                    {
                        return false;
                    }
                    for (auto const &b_entry : b)
                    {
                        auto it = a.find(get_key(b_entry));
                        if constexpr (is_map_v<T>)
                        {
                            // map: check that key is here, then also check that value is the same
                            if (a.end() == it || !(b_entry.second == it->second))
                            {
                                return false;
                            }
                        }
                        else
                        {
                            // set: only check that the key is here
                            if (a.end() == it)
                            {
                                return false;
                            }
                        }
                    }
                    return true;
                }

                friend auto operator!=(table const &a, table const &b) -> bool
                {
                    return !(a == b);
                }
            };

        } // namespace detail

        ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                class T,
                                                class Hash = hash<Key>,
                                                class KeyEqual = std::equal_to<Key>,
                                                class AllocatorOrContainer = std::allocator<std::pair<Key, T>>,
                                                class Bucket = bucket_type::standard>
        using map = detail::table<Key, T, Hash, KeyEqual, AllocatorOrContainer, Bucket, false>;

        ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                class T,
                                                class Hash = hash<Key>,
                                                class KeyEqual = std::equal_to<Key>,
                                                class AllocatorOrContainer = std::allocator<std::pair<Key, T>>,
                                                class Bucket = bucket_type::standard>
        using segmented_map = detail::table<Key, T, Hash, KeyEqual, AllocatorOrContainer, Bucket, true>;

        ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                class Hash = hash<Key>,
                                                class KeyEqual = std::equal_to<Key>,
                                                class AllocatorOrContainer = std::allocator<Key>,
                                                class Bucket = bucket_type::standard>
        using set = detail::table<Key, void, Hash, KeyEqual, AllocatorOrContainer, Bucket, false>;

        ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                class Hash = hash<Key>,
                                                class KeyEqual = std::equal_to<Key>,
                                                class AllocatorOrContainer = std::allocator<Key>,
                                                class Bucket = bucket_type::standard>
        using segmented_set = detail::table<Key, void, Hash, KeyEqual, AllocatorOrContainer, Bucket, true>;

#if defined(ANKERL_UNORDERED_DENSE_PMR)

        namespace pmr
        {

            ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                    class T,
                                                    class Hash = hash<Key>,
                                                    class KeyEqual = std::equal_to<Key>,
                                                    class Bucket = bucket_type::standard>
            using map =
                detail::table<Key, T, Hash, KeyEqual, ANKERL_UNORDERED_DENSE_PMR::polymorphic_allocator<std::pair<Key, T>>, Bucket, false>;

            ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                    class T,
                                                    class Hash = hash<Key>,
                                                    class KeyEqual = std::equal_to<Key>,
                                                    class Bucket = bucket_type::standard>
            using segmented_map =
                detail::table<Key, T, Hash, KeyEqual, ANKERL_UNORDERED_DENSE_PMR::polymorphic_allocator<std::pair<Key, T>>, Bucket, true>;

            ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                    class Hash = hash<Key>,
                                                    class KeyEqual = std::equal_to<Key>,
                                                    class Bucket = bucket_type::standard>
            using set = detail::table<Key, void, Hash, KeyEqual, ANKERL_UNORDERED_DENSE_PMR::polymorphic_allocator<Key>, Bucket, false>;

            ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                                    class Hash = hash<Key>,
                                                    class KeyEqual = std::equal_to<Key>,
                                                    class Bucket = bucket_type::standard>
            using segmented_set =
                detail::table<Key, void, Hash, KeyEqual, ANKERL_UNORDERED_DENSE_PMR::polymorphic_allocator<Key>, Bucket, true>;

        } // namespace pmr

#endif

        // deduction guides ///////////////////////////////////////////////////////////

        // deduction guides for alias templates are only possible since C++20
        // see https://en.cppreference.com/w/cpp/language/class_template_argument_deduction

    } // namespace ANKERL_UNORDERED_DENSE_NAMESPACE
} // namespace ankerl::unordered_dense

// std extensions /////////////////////////////////////////////////////////////

namespace std
{ // NOLINT(cert-dcl58-cpp)

    ANKERL_UNORDERED_DENSE_EXPORT template <class Key,
                                            class T,
                                            class Hash,
                                            class KeyEqual,
                                            class AllocatorOrContainer,
                                            class Bucket,
                                            class Pred,
                                            bool IsSegmented>
    // NOLINTNEXTLINE(cert-dcl58-cpp)
    auto erase_if(ankerl::unordered_dense::detail::table<Key, T, Hash, KeyEqual, AllocatorOrContainer, Bucket, IsSegmented> &map,
                  Pred pred) -> size_t
    {
        using map_t = ankerl::unordered_dense::detail::table<Key, T, Hash, KeyEqual, AllocatorOrContainer, Bucket, IsSegmented>;

        // going back to front because erase() invalidates the end iterator
        auto const old_size = map.size();
        auto idx = old_size;
        while (idx)
        {
            --idx;
            auto it = map.begin() + static_cast<typename map_t::difference_type>(idx);
            if (pred(*it))
            {
                map.erase(it);
            }
        }

        return old_size - map.size();
    }

} // namespace std

#endif
#endif