//                 ______  _____                 ______                _________
//  ______________ ___  /_ ___(_)_______         ___  /_ ______ ______ ______  /
//  __  ___/_  __ \__  __ \__  / __  __ \        __  __ \_  __ \_  __ \_  __  /
//  _  /    / /_/ /_  /_/ /_  /  _  / / /        _  / / // /_/ // /_/ // /_/ /
//  /_/     \____/ /_.___/ /_/   /_/ /_/ ________/_/ /_/ \____/ \____/ \__,_/
//                                      _/_____/
//
// Fast & memory efficient hashtable based on robin hood hashing for C++11/14/17/20
// https://github.com/martinus/robin-hood-hashing
//
// Licensed under the MIT License <http://opensource.org/licenses/MIT>.
// SPDX-License-Identifier: MIT
// Copyright (c) 2018-2020 Martin Ankerl <http://martin.ankerl.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 ROBIN_HOOD_H_INCLUDED
#define ROBIN_HOOD_H_INCLUDED

// see https://semver.org/
#define ROBIN_HOOD_VERSION_MAJOR 3  // for incompatible API changes
#define ROBIN_HOOD_VERSION_MINOR 10 // for adding functionality in a backwards-compatible manner
#define ROBIN_HOOD_VERSION_PATCH 0  // for backwards-compatible bug fixes

#include <algorithm>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <memory> // only to support hash of smart pointers
#include <stdexcept>
#include <string>
#include <type_traits>
#include <utility>
#if __cplusplus >= 201703L
#    include <string_view>
#endif

// #define ROBIN_HOOD_LOG_ENABLED
#ifdef ROBIN_HOOD_LOG_ENABLED
#    include <iostream>
#    define ROBIN_HOOD_LOG(...) \
        std::cout << __FUNCTION__ << "@" << __LINE__ << ": " << __VA_ARGS__ << std::endl;
#else
#    define ROBIN_HOOD_LOG(x)
#endif

// #define ROBIN_HOOD_TRACE_ENABLED
#ifdef ROBIN_HOOD_TRACE_ENABLED
#    include <iostream>
#    define ROBIN_HOOD_TRACE(...) \
        std::cout << __FUNCTION__ << "@" << __LINE__ << ": " << __VA_ARGS__ << std::endl;
#else
#    define ROBIN_HOOD_TRACE(x)
#endif

// #define ROBIN_HOOD_COUNT_ENABLED
#ifdef ROBIN_HOOD_COUNT_ENABLED
#    include <iostream>
#    define ROBIN_HOOD_COUNT(x) ++counts().x;
namespace robin_hood {
	struct Counts {
		uint64_t shiftUp{};
		uint64_t shiftDown{};
	};
	inline std::ostream& operator<<(std::ostream& os, Counts const& c) {
		return os << c.shiftUp << " shiftUp" << std::endl << c.shiftDown << " shiftDown" << std::endl;
	}

	static Counts& counts() {
		static Counts counts{};
		return counts;
	}
} // namespace robin_hood
#else
#    define ROBIN_HOOD_COUNT(x)
#endif

// all non-argument macros should use this facility. See
// https://www.fluentcpp.com/2019/05/28/better-macros-better-flags/
#define ROBIN_HOOD(x) ROBIN_HOOD_PRIVATE_DEFINITION_##x()

// mark unused members with this macro
#define ROBIN_HOOD_UNUSED(identifier)

// bitness
#if SIZE_MAX == UINT32_MAX
#    define ROBIN_HOOD_PRIVATE_DEFINITION_BITNESS() 32
#elif SIZE_MAX == UINT64_MAX
#    define ROBIN_HOOD_PRIVATE_DEFINITION_BITNESS() 64
#else
#    error Unsupported bitness
#endif

// endianess
#ifdef _MSC_VER
#    define ROBIN_HOOD_PRIVATE_DEFINITION_LITTLE_ENDIAN() 1
#    define ROBIN_HOOD_PRIVATE_DEFINITION_BIG_ENDIAN() 0
#else
#    define ROBIN_HOOD_PRIVATE_DEFINITION_LITTLE_ENDIAN() \
        (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
#    define ROBIN_HOOD_PRIVATE_DEFINITION_BIG_ENDIAN() (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
#endif

// inline
#ifdef _MSC_VER
#    define ROBIN_HOOD_PRIVATE_DEFINITION_NOINLINE() __declspec(noinline)
#else
#    define ROBIN_HOOD_PRIVATE_DEFINITION_NOINLINE() __attribute__((noinline))
#endif

// exceptions
#if !defined(__cpp_exceptions) && !defined(__EXCEPTIONS) && !defined(_CPPUNWIND)
#    define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_EXCEPTIONS() 0
#else
#    define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_EXCEPTIONS() 1
#endif

// count leading/trailing bits
#if !defined(ROBIN_HOOD_DISABLE_INTRINSICS)
#    ifdef _MSC_VER
#        if ROBIN_HOOD(BITNESS) == 32
#            define ROBIN_HOOD_PRIVATE_DEFINITION_BITSCANFORWARD() _BitScanForward
#        else
#            define ROBIN_HOOD_PRIVATE_DEFINITION_BITSCANFORWARD() _BitScanForward64
#        endif
#        include <intrin.h>
#        pragma intrinsic(ROBIN_HOOD(BITSCANFORWARD))
#        define ROBIN_HOOD_COUNT_TRAILING_ZEROES(x)                                       \
            [](size_t mask) noexcept -> int {                                             \
                unsigned long index;                                                      \
                return ROBIN_HOOD(BITSCANFORWARD)(&index, mask) ? static_cast<int>(index) \
                                                                : ROBIN_HOOD(BITNESS);    \
            }(x)
#    else
#        if ROBIN_HOOD(BITNESS) == 32
#            define ROBIN_HOOD_PRIVATE_DEFINITION_CTZ() __builtin_ctzl
#            define ROBIN_HOOD_PRIVATE_DEFINITION_CLZ() __builtin_clzl
#        else
#            define ROBIN_HOOD_PRIVATE_DEFINITION_CTZ() __builtin_ctzll
#            define ROBIN_HOOD_PRIVATE_DEFINITION_CLZ() __builtin_clzll
#        endif
#        define ROBIN_HOOD_COUNT_LEADING_ZEROES(x) ((x) ? ROBIN_HOOD(CLZ)(x) : ROBIN_HOOD(BITNESS))
#        define ROBIN_HOOD_COUNT_TRAILING_ZEROES(x) ((x) ? ROBIN_HOOD(CTZ)(x) : ROBIN_HOOD(BITNESS))
#    endif
#endif

// fallthrough
#ifndef __has_cpp_attribute // For backwards compatibility
#    define __has_cpp_attribute(x) 0
#endif
#if __has_cpp_attribute(clang::fallthrough)
#    define ROBIN_HOOD_PRIVATE_DEFINITION_FALLTHROUGH() [[clang::fallthrough]]
#elif __has_cpp_attribute(gnu::fallthrough)
#    define ROBIN_HOOD_PRIVATE_DEFINITION_FALLTHROUGH() [[gnu::fallthrough]]
#else
#    define ROBIN_HOOD_PRIVATE_DEFINITION_FALLTHROUGH()
#endif

// likely/unlikely
#ifdef _MSC_VER
#    define ROBIN_HOOD_LIKELY(condition) condition
#    define ROBIN_HOOD_UNLIKELY(condition) condition
#else
#    define ROBIN_HOOD_LIKELY(condition) __builtin_expect(condition, 1)
#    define ROBIN_HOOD_UNLIKELY(condition) __builtin_expect(condition, 0)
#endif

// detect if native wchar_t type is availiable in MSVC
#ifdef _MSC_VER
#    ifdef _NATIVE_WCHAR_T_DEFINED
#        define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_NATIVE_WCHART() 1
#    else
#        define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_NATIVE_WCHART() 0
#    endif
#else
#    define ROBIN_HOOD_PRIVATE_DEFINITION_HAS_NATIVE_WCHART() 1
#endif

// workaround missing "is_trivially_copyable" in g++ < 5.0
// See https://stackoverflow.com/a/31798726/48181
#if defined(__GNUC__) && __GNUC__ < 5
#    define ROBIN_HOOD_IS_TRIVIALLY_COPYABLE(...) __has_trivial_copy(__VA_ARGS__)
#else
#    define ROBIN_HOOD_IS_TRIVIALLY_COPYABLE(...) std::is_trivially_copyable<__VA_ARGS__>::value
#endif

// helpers for C++ versions, see https://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html
#define ROBIN_HOOD_PRIVATE_DEFINITION_CXX() __cplusplus
#define ROBIN_HOOD_PRIVATE_DEFINITION_CXX98() 199711L
#define ROBIN_HOOD_PRIVATE_DEFINITION_CXX11() 201103L
#define ROBIN_HOOD_PRIVATE_DEFINITION_CXX14() 201402L
#define ROBIN_HOOD_PRIVATE_DEFINITION_CXX17() 201703L

#if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX17)
#    define ROBIN_HOOD_PRIVATE_DEFINITION_NODISCARD() [[nodiscard]]
#else
#    define ROBIN_HOOD_PRIVATE_DEFINITION_NODISCARD()
#endif

namespace robin_hood {

#if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX14)
#    define ROBIN_HOOD_STD std
#else

	// c++11 compatibility layer
	namespace ROBIN_HOOD_STD {
		template <class T>
		struct alignment_of
			: std::integral_constant<std::size_t, alignof(typename std::remove_all_extents<T>::type)> {};

		template <class T, T... Ints>
		class integer_sequence {
		public:
			using value_type = T;
			static_assert(std::is_integral<value_type>::value, "not integral type");
			static constexpr std::size_t size() noexcept {
				return sizeof...(Ints);
			}
		};
		template <std::size_t... Inds>
		using index_sequence = integer_sequence<std::size_t, Inds...>;

		namespace detail_ {
			template <class T, T Begin, T End, bool>
			struct IntSeqImpl {
				using TValue = T;
				static_assert(std::is_integral<TValue>::value, "not integral type");
				static_assert(Begin >= 0 && Begin < End, "unexpected argument (Begin<0 || Begin<=End)");

				template <class, class>
				struct IntSeqCombiner;

				template <TValue... Inds0, TValue... Inds1>
				struct IntSeqCombiner<integer_sequence<TValue, Inds0...>, integer_sequence<TValue, Inds1...>> {
					using TResult = integer_sequence<TValue, Inds0..., Inds1...>;
				};

				using TResult =
					typename IntSeqCombiner<typename IntSeqImpl<TValue, Begin, Begin + (End - Begin) / 2,
					(End - Begin) / 2 == 1>::TResult,
					typename IntSeqImpl<TValue, Begin + (End - Begin) / 2, End,
					(End - Begin + 1) / 2 == 1>::TResult>::TResult;
			};

			template <class T, T Begin>
			struct IntSeqImpl<T, Begin, Begin, false> {
				using TValue = T;
				static_assert(std::is_integral<TValue>::value, "not integral type");
				static_assert(Begin >= 0, "unexpected argument (Begin<0)");
				using TResult = integer_sequence<TValue>;
			};

			template <class T, T Begin, T End>
			struct IntSeqImpl<T, Begin, End, true> {
				using TValue = T;
				static_assert(std::is_integral<TValue>::value, "not integral type");
				static_assert(Begin >= 0, "unexpected argument (Begin<0)");
				using TResult = integer_sequence<TValue, Begin>;
			};
		} // namespace detail_

		template <class T, T N>
		using make_integer_sequence = typename detail_::IntSeqImpl<T, 0, N, (N - 0) == 1>::TResult;

		template <std::size_t N>
		using make_index_sequence = make_integer_sequence<std::size_t, N>;

		template <class... T>
		using index_sequence_for = make_index_sequence<sizeof...(T)>;

	} // namespace ROBIN_HOOD_STD

#endif

	namespace detail {

		// make sure we static_cast to the correct type for hash_int
#if ROBIN_HOOD(BITNESS) == 64
		using SizeT = uint64_t;
#else
		using SizeT = uint32_t;
#endif

		template <typename T>
		T rotr(T x, unsigned k) {
			return (x >> k) | (x << (8U * sizeof(T) - k));
		}

		// This cast gets rid of warnings like "cast from 'uint8_t*' {aka 'unsigned char*'} to
		// 'uint64_t*' {aka 'long unsigned int*'} increases required alignment of target type". Use with
		// care!
		template <typename T>
		inline T reinterpret_cast_no_cast_align_warning(void* ptr) noexcept {
			return reinterpret_cast<T>(ptr);
		}

		template <typename T>
		inline T reinterpret_cast_no_cast_align_warning(void const* ptr) noexcept {
			return reinterpret_cast<T>(ptr);
		}

		// 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.
		template <typename E, typename... Args>
		[[noreturn]] ROBIN_HOOD(NOINLINE)
#if ROBIN_HOOD(HAS_EXCEPTIONS)
			void doThrow(Args&&... args) {
			// NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-array-to-pointer-decay)
			throw E(std::forward<Args>(args)...);
		}
#else
			void doThrow(Args&&... ROBIN_HOOD_UNUSED(args) /*unused*/) {
			abort();
		}
#endif

		template <typename E, typename T, typename... Args>
		T* assertNotNull(T* t, Args&&... args) {
			if (ROBIN_HOOD_UNLIKELY(nullptr == t)) {
				doThrow<E>(std::forward<Args>(args)...);
			}
			return t;
		}

		template <typename T>
		inline T unaligned_load(void const* ptr) noexcept {
			// using memcpy so we don't get into unaligned load problems.
			// compiler should optimize this very well anyways.
			T t;
			std::memcpy(&t, ptr, sizeof(T));
			return t;
		}

		// Allocates bulks of memory for objects of type T. This deallocates the memory in the destructor,
		// and keeps a linked list of the allocated memory around. Overhead per allocation is the size of a
		// pointer.
		template <typename T, size_t MinNumAllocs = 4, size_t MaxNumAllocs = 256>
		class BulkPoolAllocator {
		public:
			BulkPoolAllocator() noexcept = default;

			// does not copy anything, just creates a new allocator.
			BulkPoolAllocator(const BulkPoolAllocator& ROBIN_HOOD_UNUSED(o) /*unused*/) noexcept
				: mHead(nullptr)
				, mListForFree(nullptr) {}

			BulkPoolAllocator(BulkPoolAllocator&& o) noexcept
				: mHead(o.mHead)
				, mListForFree(o.mListForFree) {
				o.mListForFree = nullptr;
				o.mHead = nullptr;
			}

			BulkPoolAllocator& operator=(BulkPoolAllocator&& o) noexcept {
				reset();
				mHead = o.mHead;
				mListForFree = o.mListForFree;
				o.mListForFree = nullptr;
				o.mHead = nullptr;
				return *this;
			}

			BulkPoolAllocator&
				// NOLINTNEXTLINE(bugprone-unhandled-self-assignment,cert-oop54-cpp)
				operator=(const BulkPoolAllocator& ROBIN_HOOD_UNUSED(o) /*unused*/) noexcept {
				// does not do anything
				return *this;
			}

			~BulkPoolAllocator() noexcept {
				reset();
			}

			// Deallocates all allocated memory.
			void reset() noexcept {
				while (mListForFree) {
					T* tmp = *mListForFree;
					ROBIN_HOOD_LOG("std::free")
						std::free(mListForFree);
					mListForFree = reinterpret_cast_no_cast_align_warning<T**>(tmp);
				}
				mHead = nullptr;
			}

			// allocates, but does NOT initialize. Use in-place new constructor, e.g.
			//   T* obj = pool.allocate();
			//   ::new (static_cast<void*>(obj)) T();
			T* allocate() {
				T* tmp = mHead;
				if (!tmp) {
					tmp = performAllocation();
				}

				mHead = *reinterpret_cast_no_cast_align_warning<T**>(tmp);
				return tmp;
			}

			// does not actually deallocate but puts it in store.
			// make sure you have already called the destructor! e.g. with
			//  obj->~T();
			//  pool.deallocate(obj);
			void deallocate(T* obj) noexcept {
				*reinterpret_cast_no_cast_align_warning<T**>(obj) = mHead;
				mHead = obj;
			}

			// Adds an already allocated block of memory to the allocator. This allocator is from now on
			// responsible for freeing the data (with free()). If the provided data is not large enough to
			// make use of, it is immediately freed. Otherwise it is reused and freed in the destructor.
			void addOrFree(void* ptr, const size_t numBytes) noexcept {
				// calculate number of available elements in ptr
				if (numBytes < ALIGNMENT + ALIGNED_SIZE) {
					// not enough data for at least one element. Free and return.
					ROBIN_HOOD_LOG("std::free")
						std::free(ptr);
				}
				else {
					ROBIN_HOOD_LOG("add to buffer")
						add(ptr, numBytes);
				}
			}

			void swap(BulkPoolAllocator<T, MinNumAllocs, MaxNumAllocs>& other) noexcept {
				using std::swap;
				swap(mHead, other.mHead);
				swap(mListForFree, other.mListForFree);
			}

		private:
			// iterates the list of allocated memory to calculate how many to alloc next.
			// Recalculating this each time saves us a size_t member.
			// This ignores the fact that memory blocks might have been added manually with addOrFree. In
			// practice, this should not matter much.
			ROBIN_HOOD(NODISCARD) size_t calcNumElementsToAlloc() const noexcept {
				auto tmp = mListForFree;
				size_t numAllocs = MinNumAllocs;

				while (numAllocs * 2 <= MaxNumAllocs && tmp) {
					auto x = reinterpret_cast<T***>(tmp);
					tmp = *x;
					numAllocs *= 2;
				}

				return numAllocs;
			}

			// WARNING: Underflow if numBytes < ALIGNMENT! This is guarded in addOrFree().
			void add(void* ptr, const size_t numBytes) noexcept {
				const size_t numElements = (numBytes - ALIGNMENT) / ALIGNED_SIZE;

				auto data = reinterpret_cast<T**>(ptr);

				// link free list
				auto x = reinterpret_cast<T***>(data);
				*x = mListForFree;
				mListForFree = data;

				// create linked list for newly allocated data
				auto* const headT =
					reinterpret_cast_no_cast_align_warning<T*>(reinterpret_cast<char*>(ptr) + ALIGNMENT);

				auto* const head = reinterpret_cast<char*>(headT);

				// Visual Studio compiler automatically unrolls this loop, which is pretty cool
				for (size_t i = 0; i < numElements; ++i) {
					*reinterpret_cast_no_cast_align_warning<char**>(head + i * ALIGNED_SIZE) =
						head + (i + 1) * ALIGNED_SIZE;
				}

				// last one points to 0
				*reinterpret_cast_no_cast_align_warning<T**>(head + (numElements - 1) * ALIGNED_SIZE) =
					mHead;
				mHead = headT;
			}

			// Called when no memory is available (mHead == 0).
			// Don't inline this slow path.
			ROBIN_HOOD(NOINLINE) T* performAllocation() {
				size_t const numElementsToAlloc = calcNumElementsToAlloc();

				// alloc new memory: [prev |T, T, ... T]
				size_t const bytes = ALIGNMENT + ALIGNED_SIZE * numElementsToAlloc;
				ROBIN_HOOD_LOG("std::malloc " << bytes << " = " << ALIGNMENT << " + " << ALIGNED_SIZE
					<< " * " << numElementsToAlloc)
					add(assertNotNull<std::bad_alloc>(std::malloc(bytes)), bytes);
				return mHead;
			}

			// enforce byte alignment of the T's
#if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX14)
			static constexpr size_t ALIGNMENT =
				(std::max)(std::alignment_of<T>::value, std::alignment_of<T*>::value);
#else
			static const size_t ALIGNMENT =
				(ROBIN_HOOD_STD::alignment_of<T>::value > ROBIN_HOOD_STD::alignment_of<T*>::value)
				? ROBIN_HOOD_STD::alignment_of<T>::value
				: +ROBIN_HOOD_STD::alignment_of<T*>::value; // the + is for walkarround
#endif

			static constexpr size_t ALIGNED_SIZE = ((sizeof(T) - 1) / ALIGNMENT + 1) * ALIGNMENT;

			static_assert(MinNumAllocs >= 1, "MinNumAllocs");
			static_assert(MaxNumAllocs >= MinNumAllocs, "MaxNumAllocs");
			static_assert(ALIGNED_SIZE >= sizeof(T*), "ALIGNED_SIZE");
			static_assert(0 == (ALIGNED_SIZE % sizeof(T*)), "ALIGNED_SIZE mod");
			static_assert(ALIGNMENT >= sizeof(T*), "ALIGNMENT");

			T* mHead{ nullptr };
			T** mListForFree{ nullptr };
		};

		template <typename T, size_t MinSize, size_t MaxSize, bool IsFlat>
		struct NodeAllocator;

		// dummy allocator that does nothing
		template <typename T, size_t MinSize, size_t MaxSize>
		struct NodeAllocator<T, MinSize, MaxSize, true> {

			// we are not using the data, so just free it.
			void addOrFree(void* ptr, size_t ROBIN_HOOD_UNUSED(numBytes) /*unused*/) noexcept {
				ROBIN_HOOD_LOG("std::free")
					std::free(ptr);
			}
		};

		template <typename T, size_t MinSize, size_t MaxSize>
		struct NodeAllocator<T, MinSize, MaxSize, false> : public BulkPoolAllocator<T, MinSize, MaxSize> {};

		// dummy hash, unsed as mixer when robin_hood::hash is already used
		template <typename T>
		struct identity_hash {
			constexpr size_t operator()(T const& obj) const noexcept {
				return static_cast<size_t>(obj);
			}
		};

		// c++14 doesn't have is_nothrow_swappable, and clang++ 6.0.1 doesn't like it either, so I'm making
		// my own here.
		namespace swappable {
#if ROBIN_HOOD(CXX) < ROBIN_HOOD(CXX17)
			using std::swap;
			template <typename T>
			struct nothrow {
				static const bool value = noexcept(swap(std::declval<T&>(), std::declval<T&>()));
			};
#else
			template <typename T>
			struct nothrow {
				static const bool value = std::is_nothrow_swappable<T>::value;
			};
#endif
		} // namespace swappable

	} // namespace detail

	struct is_transparent_tag {};

	// A custom pair implementation is used in the map because std::pair is not is_trivially_copyable,
	// which means it would  not be allowed to be used in std::memcpy. This struct is copyable, which is
	// also tested.
	template <typename T1, typename T2>
	struct pair {
		using first_type = T1;
		using second_type = T2;

		template <typename U1 = T1, typename U2 = T2,
			typename = typename std::enable_if<std::is_default_constructible<U1>::value&&
			std::is_default_constructible<U2>::value>::type>
			constexpr pair() noexcept(noexcept(U1()) && noexcept(U2()))
			: first()
			, second() {}

		// pair constructors are explicit so we don't accidentally call this ctor when we don't have to.
		explicit constexpr pair(std::pair<T1, T2> const& o) noexcept(
			noexcept(T1(std::declval<T1 const&>())) && noexcept(T2(std::declval<T2 const&>())))
			: first(o.first)
			, second(o.second) {}

		// pair constructors are explicit so we don't accidentally call this ctor when we don't have to.
		explicit constexpr pair(std::pair<T1, T2>&& o) noexcept(noexcept(
			T1(std::move(std::declval<T1&&>()))) && noexcept(T2(std::move(std::declval<T2&&>()))))
			: first(std::move(o.first))
			, second(std::move(o.second)) {}

		constexpr pair(T1&& a, T2&& b) noexcept(noexcept(
			T1(std::move(std::declval<T1&&>()))) && noexcept(T2(std::move(std::declval<T2&&>()))))
			: first(std::move(a))
			, second(std::move(b)) {}

		template <typename U1, typename U2>
		constexpr pair(U1&& a, U2&& b) noexcept(noexcept(T1(std::forward<U1>(
			std::declval<U1&&>()))) && noexcept(T2(std::forward<U2>(std::declval<U2&&>()))))
			: first(std::forward<U1>(a))
			, second(std::forward<U2>(b)) {}

		template <typename... U1, typename... U2>
		constexpr pair(
			std::piecewise_construct_t /*unused*/, std::tuple<U1...> a,
			std::tuple<U2...> b) noexcept(noexcept(pair(std::declval<std::tuple<U1...>&>(),
				std::declval<std::tuple<U2...>&>(),
				ROBIN_HOOD_STD::index_sequence_for<U1...>(),
				ROBIN_HOOD_STD::index_sequence_for<U2...>())))
			: pair(a, b, ROBIN_HOOD_STD::index_sequence_for<U1...>(),
				ROBIN_HOOD_STD::index_sequence_for<U2...>()) {}

		// constructor called from the std::piecewise_construct_t ctor
		template <typename... U1, size_t... I1, typename... U2, size_t... I2>
		pair(std::tuple<U1...>& a, std::tuple<U2...>& b, ROBIN_HOOD_STD::index_sequence<I1...> /*unused*/, ROBIN_HOOD_STD::index_sequence<I2...> /*unused*/) noexcept(
			noexcept(T1(std::forward<U1>(std::get<I1>(
				std::declval<std::tuple<
				U1...>&>()))...)) && noexcept(T2(std::
					forward<U2>(std::get<I2>(
						std::declval<std::tuple<U2...>&>()))...)))
			: first(std::forward<U1>(std::get<I1>(a))...)
			, second(std::forward<U2>(std::get<I2>(b))...) {
			// make visual studio compiler happy about warning about unused a & b.
			// Visual studio's pair implementation disables warning 4100.
			(void)a;
			(void)b;
		}

		void swap(pair<T1, T2>& o) noexcept((detail::swappable::nothrow<T1>::value) &&
			(detail::swappable::nothrow<T2>::value)) {
			using std::swap;
			swap(first, o.first);
			swap(second, o.second);
		}

		T1 first;  // NOLINT(misc-non-private-member-variables-in-classes)
		T2 second; // NOLINT(misc-non-private-member-variables-in-classes)
	};

	template <typename A, typename B>
	inline void swap(pair<A, B>& a, pair<A, B>& b) noexcept(
		noexcept(std::declval<pair<A, B>&>().swap(std::declval<pair<A, B>&>()))) {
		a.swap(b);
	}

	template <typename A, typename B>
	inline constexpr bool operator==(pair<A, B> const& x, pair<A, B> const& y) {
		return (x.first == y.first) && (x.second == y.second);
	}
	template <typename A, typename B>
	inline constexpr bool operator!=(pair<A, B> const& x, pair<A, B> const& y) {
		return !(x == y);
	}
	template <typename A, typename B>
	inline constexpr bool operator<(pair<A, B> const& x, pair<A, B> const& y) noexcept(noexcept(
		std::declval<A const&>() < std::declval<A const&>()) && noexcept(std::declval<B const&>() <
			std::declval<B const&>())) {
		return x.first < y.first || (!(y.first < x.first) && x.second < y.second);
	}
	template <typename A, typename B>
	inline constexpr bool operator>(pair<A, B> const& x, pair<A, B> const& y) {
		return y < x;
	}
	template <typename A, typename B>
	inline constexpr bool operator<=(pair<A, B> const& x, pair<A, B> const& y) {
		return !(x > y);
	}
	template <typename A, typename B>
	inline constexpr bool operator>=(pair<A, B> const& x, pair<A, B> const& y) {
		return !(x < y);
	}

	inline size_t hash_bytes(void const* ptr, size_t len) noexcept {
		static constexpr uint64_t m = UINT64_C(0xc6a4a7935bd1e995);
		static constexpr uint64_t seed = UINT64_C(0xe17a1465);
		static constexpr unsigned int r = 47;

		auto const* const data64 = static_cast<uint64_t const*>(ptr);
		uint64_t h = seed ^ (len * m);

		size_t const n_blocks = len / 8;
		for (size_t i = 0; i < n_blocks; ++i) {
			auto k = detail::unaligned_load<uint64_t>(data64 + i);

			k *= m;
			k ^= k >> r;
			k *= m;

			h ^= k;
			h *= m;
		}

		auto const* const data8 = reinterpret_cast<uint8_t const*>(data64 + n_blocks);
		switch (len & 7U) {
		case 7:
			h ^= static_cast<uint64_t>(data8[6]) << 48U;
			ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
		case 6:
			h ^= static_cast<uint64_t>(data8[5]) << 40U;
			ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
		case 5:
			h ^= static_cast<uint64_t>(data8[4]) << 32U;
			ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
		case 4:
			h ^= static_cast<uint64_t>(data8[3]) << 24U;
			ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
		case 3:
			h ^= static_cast<uint64_t>(data8[2]) << 16U;
			ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
		case 2:
			h ^= static_cast<uint64_t>(data8[1]) << 8U;
			ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
		case 1:
			h ^= static_cast<uint64_t>(data8[0]);
			h *= m;
			ROBIN_HOOD(FALLTHROUGH); // FALLTHROUGH
		default:
			break;
		}

		h ^= h >> r;
		h *= m;
		h ^= h >> r;
		return static_cast<size_t>(h);
	}

	inline size_t hash_int(uint64_t x) noexcept {
		// inspired by lemire's strongly universal hashing
		// https://lemire.me/blog/2018/08/15/fast-strongly-universal-64-bit-hashing-everywhere/
		//
		// Instead of shifts, we use rotations so we don't lose any bits.
		//
		// Added a final multiplcation with a constant for more mixing. It is most important that
		// the lower bits are well mixed.
		auto h1 = x * UINT64_C(0xA24BAED4963EE407);
		auto h2 = detail::rotr(x, 32U) * UINT64_C(0x9FB21C651E98DF25);
		auto h = detail::rotr(h1 + h2, 32U);
		return static_cast<size_t>(h);
	}

	// A thin wrapper around std::hash, performing an additional simple mixing step of the result.
	template <typename T, typename Enable = void>
	struct hash : public std::hash<T> {
		size_t operator()(T const& obj) const
			noexcept(noexcept(std::declval<std::hash<T>>().operator()(std::declval<T const&>()))) {
			// call base hash
			auto result = std::hash<T>::operator()(obj);
			// return mixed of that, to be save against identity has
			return hash_int(static_cast<detail::SizeT>(result));
		}
	};

	template <typename CharT>
	struct hash<std::basic_string<CharT>> {
		size_t operator()(std::basic_string<CharT> const& str) const noexcept {
			return hash_bytes(str.data(), sizeof(CharT) * str.size());
		}
	};

#if ROBIN_HOOD(CXX) >= ROBIN_HOOD(CXX17)
	template <typename CharT>
	struct hash<std::basic_string_view<CharT>> {
		size_t operator()(std::basic_string_view<CharT> const& sv) const noexcept {
			return hash_bytes(sv.data(), sizeof(CharT) * sv.size());
		}
	};
#endif

	template <class T>
	struct hash<T*> {
		size_t operator()(T* ptr) const noexcept {
			return hash_int(reinterpret_cast<detail::SizeT>(ptr));
		}
	};

	template <class T>
	struct hash<std::unique_ptr<T>> {
		size_t operator()(std::unique_ptr<T> const& ptr) const noexcept {
			return hash_int(reinterpret_cast<detail::SizeT>(ptr.get()));
		}
	};

	template <class T>
	struct hash<std::shared_ptr<T>> {
		size_t operator()(std::shared_ptr<T> const& ptr) const noexcept {
			return hash_int(reinterpret_cast<detail::SizeT>(ptr.get()));
		}
	};

	template <typename Enum>
	struct hash<Enum, typename std::enable_if<std::is_enum<Enum>::value>::type> {
		size_t operator()(Enum e) const noexcept {
			using Underlying = typename std::underlying_type<Enum>::type;
			return hash<Underlying>{}(static_cast<Underlying>(e));
		}
	};

#define ROBIN_HOOD_HASH_INT(T)                           \
    template <>                                          \
    struct hash<T> {                                     \
        size_t operator()(T const& obj) const noexcept { \
            return hash_int(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
	ROBIN_HOOD_HASH_INT(bool);
	ROBIN_HOOD_HASH_INT(char);
	ROBIN_HOOD_HASH_INT(signed char);
	ROBIN_HOOD_HASH_INT(unsigned char);
	ROBIN_HOOD_HASH_INT(char16_t);
	ROBIN_HOOD_HASH_INT(char32_t);
#if ROBIN_HOOD(HAS_NATIVE_WCHART)
	ROBIN_HOOD_HASH_INT(wchar_t);
#endif
	ROBIN_HOOD_HASH_INT(short);
	ROBIN_HOOD_HASH_INT(unsigned short);
	ROBIN_HOOD_HASH_INT(int);
	ROBIN_HOOD_HASH_INT(unsigned int);
	ROBIN_HOOD_HASH_INT(long);
	ROBIN_HOOD_HASH_INT(long long);
	ROBIN_HOOD_HASH_INT(unsigned long);
	ROBIN_HOOD_HASH_INT(unsigned long long);
#if defined(__GNUC__) && !defined(__clang__)
#    pragma GCC diagnostic pop
#endif
	namespace detail {

		template <typename T>
		struct void_type {
			using type = void;
		};

		template <typename T, typename = void>
		struct has_is_transparent : public std::false_type {};

		template <typename T>
		struct has_is_transparent<T, typename void_type<typename T::is_transparent>::type>
			: public std::true_type {};

		// using wrapper classes for hash and key_equal prevents the diamond problem when the same type
		// is used. see https://stackoverflow.com/a/28771920/48181
		template <typename T>
		struct WrapHash : public T {
			WrapHash() = default;
			explicit WrapHash(T const& o) noexcept(noexcept(T(std::declval<T const&>())))
				: T(o) {}
		};

		template <typename T>
		struct WrapKeyEqual : public T {
			WrapKeyEqual() = default;
			explicit WrapKeyEqual(T const& o) noexcept(noexcept(T(std::declval<T const&>())))
				: T(o) {}
		};

		// A highly optimized hashmap implementation, using the Robin Hood algorithm.
		//
		// In most cases, this map should be usable as a drop-in replacement for std::unordered_map, but
		// be about 2x faster in most cases and require much less allocations.
		//
		// This implementation uses the following memory layout:
		//
		// [Node, Node, ... Node | info, info, ... infoSentinel ]
		//
		// * Node: either a DataNode that directly has the std::pair<key, val> as member,
		//   or a DataNode with a pointer to std::pair<key,val>. Which DataNode representation to use
		//   depends on how fast the swap() operation is. Heuristically, this is automatically choosen
		//   based on sizeof(). there are always 2^n Nodes.
		//
		// * info: Each Node in the map has a corresponding info byte, so there are 2^n info bytes.
		//   Each byte is initialized to 0, meaning the corresponding Node is empty. Set to 1 means the
		//   corresponding node contains data. Set to 2 means the corresponding Node is filled, but it
		//   actually belongs to the previous position and was pushed out because that place is already
		//   taken.
		//
		// * infoSentinel: Sentinel byte set to 1, so that iterator's ++ can stop at end() without the
		//   need for a idx variable.
		//
		// According to STL, order of templates has effect on throughput. That's why I've moved the
		// boolean to the front.
		// https://www.reddit.com/r/cpp/comments/ahp6iu/compile_time_binary_size_reductions_and_cs_future/eeguck4/
		template <bool IsFlat, size_t MaxLoadFactor100, typename Key, typename T, typename Hash,
			typename KeyEqual>
			class Table
			: public WrapHash<Hash>,
			public WrapKeyEqual<KeyEqual>,
			detail::NodeAllocator<
			typename std::conditional<
			std::is_void<T>::value, Key,
			robin_hood::pair<typename std::conditional<IsFlat, Key, Key const>::type, T>>::type,
			4, 16384, IsFlat> {
			public:
				static constexpr bool is_flat = IsFlat;
				static constexpr bool is_map = !std::is_void<T>::value;
				static constexpr bool is_set = !is_map;
				static constexpr bool is_transparent =
					has_is_transparent<Hash>::value && has_is_transparent<KeyEqual>::value;

				using key_type = Key;
				using mapped_type = T;
				using value_type = typename std::conditional<
					is_set, Key,
					robin_hood::pair<typename std::conditional<is_flat, Key, Key const>::type, T>>::type;
				using size_type = size_t;
				using hasher = Hash;
				using key_equal = KeyEqual;
				using Self = Table<IsFlat, MaxLoadFactor100, key_type, mapped_type, hasher, key_equal>;

			private:
				static_assert(MaxLoadFactor100 > 10 && MaxLoadFactor100 < 100,
					"MaxLoadFactor100 needs to be >10 && < 100");

				using WHash = WrapHash<Hash>;
				using WKeyEqual = WrapKeyEqual<KeyEqual>;

				// configuration defaults

				// make sure we have 8 elements, needed to quickly rehash mInfo
				static constexpr size_t InitialNumElements = sizeof(uint64_t);
				static constexpr uint32_t InitialInfoNumBits = 5;
				static constexpr uint8_t InitialInfoInc = 1U << InitialInfoNumBits;
				static constexpr size_t InfoMask = InitialInfoInc - 1U;
				static constexpr uint8_t InitialInfoHashShift = 0;
				using DataPool = detail::NodeAllocator<value_type, 4, 16384, IsFlat>;

				// type needs to be wider than uint8_t.
				using InfoType = uint32_t;

				// DataNode ////////////////////////////////////////////////////////

				// Primary template for the data node. We have special implementations for small and big
				// objects. For large objects it is assumed that swap() is fairly slow, so we allocate these
				// on the heap so swap merely swaps a pointer.
				template <typename M, bool>
				class DataNode {};

				// Small: just allocate on the stack.
				template <typename M>
				class DataNode<M, true> final {
				public:
					template <typename... Args>
					explicit DataNode(M& ROBIN_HOOD_UNUSED(map) /*unused*/, Args&&... args) noexcept(
						noexcept(value_type(std::forward<Args>(args)...)))
						: mData(std::forward<Args>(args)...) {}

					DataNode(M& ROBIN_HOOD_UNUSED(map) /*unused*/, DataNode<M, true>&& n) noexcept(
						std::is_nothrow_move_constructible<value_type>::value)
						: mData(std::move(n.mData)) {}

					// doesn't do anything
					void destroy(M& ROBIN_HOOD_UNUSED(map) /*unused*/) noexcept {}
					void destroyDoNotDeallocate() noexcept {}

					value_type const* operator->() const noexcept {
						return &mData;
					}
					value_type* operator->() noexcept {
						return &mData;
					}

					const value_type& operator*() const noexcept {
						return mData;
					}

					value_type& operator*() noexcept {
						return mData;
					}

					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_map, typename VT::first_type&>::type getFirst() noexcept {
						return mData.first;
					}
					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_set, VT&>::type getFirst() noexcept {
						return mData;
					}

					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_map, typename VT::first_type const&>::type
						getFirst() const noexcept {
						return mData.first;
					}
					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_set, VT const&>::type getFirst() const noexcept {
						return mData;
					}

					template <typename MT = mapped_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_map, MT&>::type getSecond() noexcept {
						return mData.second;
					}

					template <typename MT = mapped_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_set, MT const&>::type getSecond() const noexcept {
						return mData.second;
					}

					void swap(DataNode<M, true>& o) noexcept(
						noexcept(std::declval<value_type>().swap(std::declval<value_type>()))) {
						mData.swap(o.mData);
					}

				private:
					value_type mData;
				};

				// big object: allocate on heap.
				template <typename M>
				class DataNode<M, false> {
				public:
					template <typename... Args>
					explicit DataNode(M& map, Args&&... args)
						: mData(map.allocate()) {
						::new (static_cast<void*>(mData)) value_type(std::forward<Args>(args)...);
					}

					DataNode(M& ROBIN_HOOD_UNUSED(map) /*unused*/, DataNode<M, false>&& n) noexcept
						: mData(std::move(n.mData)) {}

					void destroy(M& map) noexcept {
						// don't deallocate, just put it into list of datapool.
						mData->~value_type();
						map.deallocate(mData);
					}

					void destroyDoNotDeallocate() noexcept {
						mData->~value_type();
					}

					value_type const* operator->() const noexcept {
						return mData;
					}

					value_type* operator->() noexcept {
						return mData;
					}

					const value_type& operator*() const {
						return *mData;
					}

					value_type& operator*() {
						return *mData;
					}

					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_map, typename VT::first_type&>::type getFirst() noexcept {
						return mData->first;
					}
					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_set, VT&>::type getFirst() noexcept {
						return *mData;
					}

					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_map, typename VT::first_type const&>::type
						getFirst() const noexcept {
						return mData->first;
					}
					template <typename VT = value_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_set, VT const&>::type getFirst() const noexcept {
						return *mData;
					}

					template <typename MT = mapped_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_map, MT&>::type getSecond() noexcept {
						return mData->second;
					}

					template <typename MT = mapped_type>
					ROBIN_HOOD(NODISCARD)
						typename std::enable_if<is_map, MT const&>::type getSecond() const noexcept {
						return mData->second;
					}

					void swap(DataNode<M, false>& o) noexcept {
						using std::swap;
						swap(mData, o.mData);
					}

				private:
					value_type* mData;
				};

				using Node = DataNode<Self, IsFlat>;

				// helpers for doInsert: extract first entry (only const required)
				ROBIN_HOOD(NODISCARD) key_type const& getFirstConst(Node const& n) const noexcept {
					return n.getFirst();
				}

				// in case we have void mapped_type, we are not using a pair, thus we just route k through.
				// No need to disable this because it's just not used if not applicable.
				ROBIN_HOOD(NODISCARD) key_type const& getFirstConst(key_type const& k) const noexcept {
					return k;
				}

				// in case we have non-void mapped_type, we have a standard robin_hood::pair
				template <typename Q = mapped_type>
				ROBIN_HOOD(NODISCARD)
					typename std::enable_if<!std::is_void<Q>::value, key_type const&>::type
					getFirstConst(value_type const& vt) const noexcept {
					return vt.first;
				}

				// Cloner //////////////////////////////////////////////////////////

				template <typename M, bool UseMemcpy>
				struct Cloner;

				// fast path: Just copy data, without allocating anything.
				template <typename M>
				struct Cloner<M, true> {
					void operator()(M const& source, M& target) const {
						auto const* const src = reinterpret_cast<char const*>(source.mKeyVals);
						auto* tgt = reinterpret_cast<char*>(target.mKeyVals);
						auto const numElementsWithBuffer = target.calcNumElementsWithBuffer(target.mMask + 1);
						std::copy(src, src + target.calcNumBytesTotal(numElementsWithBuffer), tgt);
					}
				};

				template <typename M>
				struct Cloner<M, false> {
					void operator()(M const& s, M& t) const {
						auto const numElementsWithBuffer = t.calcNumElementsWithBuffer(t.mMask + 1);
						std::copy(s.mInfo, s.mInfo + t.calcNumBytesInfo(numElementsWithBuffer), t.mInfo);

						for (size_t i = 0; i < numElementsWithBuffer; ++i) {
							if (t.mInfo[i]) {
								::new (static_cast<void*>(t.mKeyVals + i)) Node(t, *s.mKeyVals[i]);
							}
						}
					}
				};

				// Destroyer ///////////////////////////////////////////////////////

				template <typename M, bool IsFlatAndTrivial>
				struct Destroyer {};

				template <typename M>
				struct Destroyer<M, true> {
					void nodes(M& m) const noexcept {
						m.mNumElements = 0;
					}

					void nodesDoNotDeallocate(M& m) const noexcept {
						m.mNumElements = 0;
					}
				};

				template <typename M>
				struct Destroyer<M, false> {
					void nodes(M& m) const noexcept {
						m.mNumElements = 0;
						// clear also resets mInfo to 0, that's sometimes not necessary.
						auto const numElementsWithBuffer = m.calcNumElementsWithBuffer(m.mMask + 1);

						for (size_t idx = 0; idx < numElementsWithBuffer; ++idx) {
							if (0 != m.mInfo[idx]) {
								Node& n = m.mKeyVals[idx];
								n.destroy(m);
								n.~Node();
							}
						}
					}

					void nodesDoNotDeallocate(M& m) const noexcept {
						m.mNumElements = 0;
						// clear also resets mInfo to 0, that's sometimes not necessary.
						auto const numElementsWithBuffer = m.calcNumElementsWithBuffer(m.mMask + 1);
						for (size_t idx = 0; idx < numElementsWithBuffer; ++idx) {
							if (0 != m.mInfo[idx]) {
								Node& n = m.mKeyVals[idx];
								n.destroyDoNotDeallocate();
								n.~Node();
							}
						}
					}
				};

				// Iter ////////////////////////////////////////////////////////////

				struct fast_forward_tag {};

				// generic iterator for both const_iterator and iterator.
				template <bool IsConst>
				// NOLINTNEXTLINE(hicpp-special-member-functions,cppcoreguidelines-special-member-functions)
				class Iter {
				private:
					using NodePtr = typename std::conditional<IsConst, Node const*, Node*>::type;

				public:
					using difference_type = std::ptrdiff_t;
					using value_type = typename Self::value_type;
					using reference = typename std::conditional<IsConst, value_type const&, value_type&>::type;
					using pointer = typename std::conditional<IsConst, value_type const*, value_type*>::type;
					using iterator_category = std::forward_iterator_tag;

					// default constructed iterator can be compared to itself, but WON'T return true when
					// compared to end().
					Iter() = default;

					// Rule of zero: nothing specified. The conversion constructor is only enabled for
					// iterator to const_iterator, so it doesn't accidentally work as a copy ctor.

					// Conversion constructor from iterator to const_iterator.
					template <bool OtherIsConst,
						typename = typename std::enable_if<IsConst && !OtherIsConst>::type>
						// NOLINTNEXTLINE(hicpp-explicit-conversions)
						Iter(Iter<OtherIsConst> const& other) noexcept
						: mKeyVals(other.mKeyVals)
						, mInfo(other.mInfo) {}

					Iter(NodePtr valPtr, uint8_t const* infoPtr) noexcept
						: mKeyVals(valPtr)
						, mInfo(infoPtr) {}

					Iter(NodePtr valPtr, uint8_t const* infoPtr,
						fast_forward_tag ROBIN_HOOD_UNUSED(tag) /*unused*/) noexcept
						: mKeyVals(valPtr)
						, mInfo(infoPtr) {
						fastForward();
					}

					template <bool OtherIsConst,
						typename = typename std::enable_if<IsConst && !OtherIsConst>::type>
						Iter& operator=(Iter<OtherIsConst> const& other) noexcept {
						mKeyVals = other.mKeyVals;
						mInfo = other.mInfo;
						return *this;
					}

					// prefix increment. Undefined behavior if we are at end()!
					Iter& operator++() noexcept {
						mInfo++;
						mKeyVals++;
						fastForward();
						return *this;
					}

					Iter operator++(int) noexcept {
						Iter tmp = *this;
						++(*this);
						return tmp;
					}

					reference operator*() const {
						return **mKeyVals;
					}

					pointer operator->() const {
						return &**mKeyVals;
					}

					template <bool O>
					bool operator==(Iter<O> const& o) const noexcept {
						return mKeyVals == o.mKeyVals;
					}

					template <bool O>
					bool operator!=(Iter<O> const& o) const noexcept {
						return mKeyVals != o.mKeyVals;
					}

				private:
					// fast forward to the next non-free info byte
					// I've tried a few variants that don't depend on intrinsics, but unfortunately they are
					// quite a bit slower than this one. So I've reverted that change again. See map_benchmark.
					void fastForward() noexcept {
						size_t n = 0;
						while (0U == (n = detail::unaligned_load<size_t>(mInfo))) {
							mInfo += sizeof(size_t);
							mKeyVals += sizeof(size_t);
						}
#if defined(ROBIN_HOOD_DISABLE_INTRINSICS)
						// we know for certain that within the next 8 bytes we'll find a non-zero one.
						if (ROBIN_HOOD_UNLIKELY(0U == detail::unaligned_load<uint32_t>(mInfo))) {
							mInfo += 4;
							mKeyVals += 4;
						}
						if (ROBIN_HOOD_UNLIKELY(0U == detail::unaligned_load<uint16_t>(mInfo))) {
							mInfo += 2;
							mKeyVals += 2;
						}
						if (ROBIN_HOOD_UNLIKELY(0U == *mInfo)) {
							mInfo += 1;
							mKeyVals += 1;
						}
#else
#    if ROBIN_HOOD(LITTLE_ENDIAN)
						auto inc = ROBIN_HOOD_COUNT_TRAILING_ZEROES(n) / 8;
#    else
						auto inc = ROBIN_HOOD_COUNT_LEADING_ZEROES(n) / 8;
#    endif
						mInfo += inc;
						mKeyVals += inc;
#endif
					}

					friend class Table<IsFlat, MaxLoadFactor100, key_type, mapped_type, hasher, key_equal>;
					NodePtr mKeyVals{ nullptr };
					uint8_t const* mInfo{ nullptr };
				};

				////////////////////////////////////////////////////////////////////

				// highly performance relevant code.
				// Lower bits are used for indexing into the array (2^n size)
				// The upper 1-5 bits need to be a reasonable good hash, to save comparisons.
				template <typename HashKey>
				void keyToIdx(HashKey&& key, size_t* idx, InfoType* info) const {
					// for a user-specified hash that is *not* robin_hood::hash, apply robin_hood::hash as
					// an additional mixing step. This serves as a bad hash prevention, if the given data is
					// badly mixed.
					using Mix =
						typename std::conditional<std::is_same<::robin_hood::hash<key_type>, hasher>::value,
						::robin_hood::detail::identity_hash<size_t>,
						::robin_hood::hash<size_t>>::type;

					// the lower InitialInfoNumBits are reserved for info.
					auto h = Mix{}(WHash::operator()(key));
					*info = mInfoInc + static_cast<InfoType>((h & InfoMask) >> mInfoHashShift);
					*idx = (h >> InitialInfoNumBits) & mMask;
				}

				// forwards the index by one, wrapping around at the end
				void next(InfoType* info, size_t* idx) const noexcept {
					*idx = *idx + 1;
					*info += mInfoInc;
				}

				void nextWhileLess(InfoType* info, size_t* idx) const noexcept {
					// unrolling this by hand did not bring any speedups.
					while (*info < mInfo[*idx]) {
						next(info, idx);
					}
				}

				// Shift everything up by one element. Tries to move stuff around.
				void
					shiftUp(size_t startIdx,
						size_t const insertion_idx) noexcept(std::is_nothrow_move_assignable<Node>::value) {
					auto idx = startIdx;
					::new (static_cast<void*>(mKeyVals + idx)) Node(std::move(mKeyVals[idx - 1]));
					while (--idx != insertion_idx) {
						mKeyVals[idx] = std::move(mKeyVals[idx - 1]);
					}

					idx = startIdx;
					while (idx != insertion_idx) {
						ROBIN_HOOD_COUNT(shiftUp)
							mInfo[idx] = static_cast<uint8_t>(mInfo[idx - 1] + mInfoInc);
						if (ROBIN_HOOD_UNLIKELY(mInfo[idx] + mInfoInc > 0xFF)) {
							mMaxNumElementsAllowed = 0;
						}
						--idx;
					}
				}

				void shiftDown(size_t idx) noexcept(std::is_nothrow_move_assignable<Node>::value) {
					// until we find one that is either empty or has zero offset.
					// TODO(martinus) we don't need to move everything, just the last one for the same
					// bucket.
					mKeyVals[idx].destroy(*this);

					// until we find one that is either empty or has zero offset.
					while (mInfo[idx + 1] >= 2 * mInfoInc) {
						ROBIN_HOOD_COUNT(shiftDown)
							mInfo[idx] = static_cast<uint8_t>(mInfo[idx + 1] - mInfoInc);
						mKeyVals[idx] = std::move(mKeyVals[idx + 1]);
						++idx;
					}

					mInfo[idx] = 0;
					// don't destroy, we've moved it
					// mKeyVals[idx].destroy(*this);
					mKeyVals[idx].~Node();
				}

				// copy of find(), except that it returns iterator instead of const_iterator.
				template <typename Other>
				ROBIN_HOOD(NODISCARD)
					size_t findIdx(Other const& key) const {
					size_t idx{};
					InfoType info{};
					keyToIdx(key, &idx, &info);

					do {
						// unrolling this twice gives a bit of a speedup. More unrolling did not help.
						if (info == mInfo[idx] &&
							ROBIN_HOOD_LIKELY(WKeyEqual::operator()(key, mKeyVals[idx].getFirst()))) {
							return idx;
						}
						next(&info, &idx);
						if (info == mInfo[idx] &&
							ROBIN_HOOD_LIKELY(WKeyEqual::operator()(key, mKeyVals[idx].getFirst()))) {
							return idx;
						}
						next(&info, &idx);
					} while (info <= mInfo[idx]);

					// nothing found!
					return mMask == 0 ? 0
						: static_cast<size_t>(std::distance(
							mKeyVals, reinterpret_cast_no_cast_align_warning<Node*>(mInfo)));
				}

				void cloneData(const Table& o) {
					Cloner<Table, IsFlat&& ROBIN_HOOD_IS_TRIVIALLY_COPYABLE(Node)>()(o, *this);
				}

				// inserts a keyval that is guaranteed to be new, e.g. when the hashmap is resized.
				// @return index where the element was created
				size_t insert_move(Node&& keyval) {
					// we don't retry, fail if overflowing
					// don't need to check max num elements
					if (0 == mMaxNumElementsAllowed && !try_increase_info()) {
						throwOverflowError(); // impossible to reach LCOV_EXCL_LINE
					}

					size_t idx{};
					InfoType info{};
					keyToIdx(keyval.getFirst(), &idx, &info);

					// skip forward. Use <= because we are certain that the element is not there.
					while (info <= mInfo[idx]) {
						idx = idx + 1;
						info += mInfoInc;
					}

					// key not found, so we are now exactly where we want to insert it.
					auto const insertion_idx = idx;
					auto const insertion_info = static_cast<uint8_t>(info);
					if (ROBIN_HOOD_UNLIKELY(insertion_info + mInfoInc > 0xFF)) {
						mMaxNumElementsAllowed = 0;
					}

					// find an empty spot
					while (0 != mInfo[idx]) {
						next(&info, &idx);
					}

					auto& l = mKeyVals[insertion_idx];
					if (idx == insertion_idx) {
						::new (static_cast<void*>(&l)) Node(std::move(keyval));
					}
					else {
						shiftUp(idx, insertion_idx);
						l = std::move(keyval);
					}

					// put at empty spot
					mInfo[insertion_idx] = insertion_info;

					++mNumElements;
					return insertion_idx;
				}

			public:
				using iterator = Iter<false>;
				using const_iterator = Iter<true>;

				Table() noexcept(noexcept(Hash()) && noexcept(KeyEqual()))
					: WHash()
					, WKeyEqual() {
					ROBIN_HOOD_TRACE(this)
				}

				// Creates an empty hash map. Nothing is allocated yet, this happens at the first insert.
				// This tremendously speeds up ctor & dtor of a map that never receives an element. The
				// penalty is payed at the first insert, and not before. Lookup of this empty map works
				// because everybody points to DummyInfoByte::b. parameter bucket_count is dictated by the
				// standard, but we can ignore it.
				explicit Table(
					size_t ROBIN_HOOD_UNUSED(bucket_count) /*unused*/, const Hash& h = Hash{},
					const KeyEqual& equal = KeyEqual{}) noexcept(noexcept(Hash(h)) && noexcept(KeyEqual(equal)))
					: WHash(h)
					, WKeyEqual(equal) {
					ROBIN_HOOD_TRACE(this)
				}

				template <typename Iter>
				Table(Iter first, Iter last, size_t ROBIN_HOOD_UNUSED(bucket_count) /*unused*/ = 0,
					const Hash& h = Hash{}, const KeyEqual& equal = KeyEqual{})
					: WHash(h)
					, WKeyEqual(equal) {
					ROBIN_HOOD_TRACE(this)
						insert(first, last);
				}

				Table(std::initializer_list<value_type> initlist,
					size_t ROBIN_HOOD_UNUSED(bucket_count) /*unused*/ = 0, const Hash& h = Hash{},
					const KeyEqual& equal = KeyEqual{})
					: WHash(h)
					, WKeyEqual(equal) {
					ROBIN_HOOD_TRACE(this)
						insert(initlist.begin(), initlist.end());
				}

				Table(Table&& o) noexcept
					: WHash(std::move(static_cast<WHash&>(o)))
					, WKeyEqual(std::move(static_cast<WKeyEqual&>(o)))
					, DataPool(std::move(static_cast<DataPool&>(o))) {
					ROBIN_HOOD_TRACE(this)
						if (o.mMask) {
							mKeyVals = std::move(o.mKeyVals);
							mInfo = std::move(o.mInfo);
							mNumElements = std::move(o.mNumElements);
							mMask = std::move(o.mMask);
							mMaxNumElementsAllowed = std::move(o.mMaxNumElementsAllowed);
							mInfoInc = std::move(o.mInfoInc);
							mInfoHashShift = std::move(o.mInfoHashShift);
							// set other's mask to 0 so its destructor won't do anything
							o.init();
						}
				}

				Table& operator=(Table&& o) noexcept {
					ROBIN_HOOD_TRACE(this)
						if (&o != this) {
							if (o.mMask) {
								// only move stuff if the other map actually has some data
								destroy();
								mKeyVals = std::move(o.mKeyVals);
								mInfo = std::move(o.mInfo);
								mNumElements = std::move(o.mNumElements);
								mMask = std::move(o.mMask);
								mMaxNumElementsAllowed = std::move(o.mMaxNumElementsAllowed);
								mInfoInc = std::move(o.mInfoInc);
								mInfoHashShift = std::move(o.mInfoHashShift);
								WHash::operator=(std::move(static_cast<WHash&>(o)));
								WKeyEqual::operator=(std::move(static_cast<WKeyEqual&>(o)));
								DataPool::operator=(std::move(static_cast<DataPool&>(o)));

								o.init();

							}
							else {
								// nothing in the other map => just clear us.
								clear();
							}
						}
					return *this;
				}

				Table(const Table& o)
					: WHash(static_cast<const WHash&>(o))
					, WKeyEqual(static_cast<const WKeyEqual&>(o))
					, DataPool(static_cast<const DataPool&>(o)) {
					ROBIN_HOOD_TRACE(this)
						if (!o.empty()) {
							// not empty: create an exact copy. it is also possible to just iterate through all
							// elements and insert them, but copying is probably faster.

							auto const numElementsWithBuffer = calcNumElementsWithBuffer(o.mMask + 1);
							auto const numBytesTotal = calcNumBytesTotal(numElementsWithBuffer);

							ROBIN_HOOD_LOG("std::malloc " << numBytesTotal << " = calcNumBytesTotal("
								<< numElementsWithBuffer << ")")
								mKeyVals = static_cast<Node*>(
									detail::assertNotNull<std::bad_alloc>(std::malloc(numBytesTotal)));
							// no need for calloc because clonData does memcpy
							mInfo = reinterpret_cast<uint8_t*>(mKeyVals + numElementsWithBuffer);
							mNumElements = o.mNumElements;
							mMask = o.mMask;
							mMaxNumElementsAllowed = o.mMaxNumElementsAllowed;
							mInfoInc = o.mInfoInc;
							mInfoHashShift = o.mInfoHashShift;
							cloneData(o);
						}
				}

				// Creates a copy of the given map. Copy constructor of each entry is used.
				// Not sure why clang-tidy thinks this doesn't handle self assignment, it does
				// NOLINTNEXTLINE(bugprone-unhandled-self-assignment,cert-oop54-cpp)
				Table& operator=(Table const& o) {
					ROBIN_HOOD_TRACE(this)
						if (&o == this) {
							// prevent assigning of itself
							return *this;
						}

					// we keep using the old allocator and not assign the new one, because we want to keep
					// the memory available. when it is the same size.
					if (o.empty()) {
						if (0 == mMask) {
							// nothing to do, we are empty too
							return *this;
						}

						// not empty: destroy what we have there
						// clear also resets mInfo to 0, that's sometimes not necessary.
						destroy();
						init();
						WHash::operator=(static_cast<const WHash&>(o));
						WKeyEqual::operator=(static_cast<const WKeyEqual&>(o));
						DataPool::operator=(static_cast<DataPool const&>(o));

						return *this;
					}

					// clean up old stuff
					Destroyer<Self, IsFlat&& std::is_trivially_destructible<Node>::value>{}.nodes(*this);

					if (mMask != o.mMask) {
						// no luck: we don't have the same array size allocated, so we need to realloc.
						if (0 != mMask) {
							// only deallocate if we actually have data!
							ROBIN_HOOD_LOG("std::free")
								std::free(mKeyVals);
						}

						auto const numElementsWithBuffer = calcNumElementsWithBuffer(o.mMask + 1);
						auto const numBytesTotal = calcNumBytesTotal(numElementsWithBuffer);
						ROBIN_HOOD_LOG("std::malloc " << numBytesTotal << " = calcNumBytesTotal("
							<< numElementsWithBuffer << ")")
							mKeyVals = static_cast<Node*>(
								detail::assertNotNull<std::bad_alloc>(std::malloc(numBytesTotal)));

						// no need for calloc here because cloneData performs a memcpy.
						mInfo = reinterpret_cast<uint8_t*>(mKeyVals + numElementsWithBuffer);
						// sentinel is set in cloneData
					}
					WHash::operator=(static_cast<const WHash&>(o));
					WKeyEqual::operator=(static_cast<const WKeyEqual&>(o));
					DataPool::operator=(static_cast<DataPool const&>(o));
					mNumElements = o.mNumElements;
					mMask = o.mMask;
					mMaxNumElementsAllowed = o.mMaxNumElementsAllowed;
					mInfoInc = o.mInfoInc;
					mInfoHashShift = o.mInfoHashShift;
					cloneData(o);

					return *this;
				}

				// Swaps everything between the two maps.
				void swap(Table& o) {
					ROBIN_HOOD_TRACE(this)
						using std::swap;
					swap(o, *this);
				}

				// Clears all data, without resizing.
				void clear() {
					ROBIN_HOOD_TRACE(this)
						if (empty()) {
							// don't do anything! also important because we don't want to write to
							// DummyInfoByte::b, even though we would just write 0 to it.
							return;
						}

					Destroyer<Self, IsFlat&& std::is_trivially_destructible<Node>::value>{}.nodes(*this);

					auto const numElementsWithBuffer = calcNumElementsWithBuffer(mMask + 1);
					// clear everything, then set the sentinel again
					uint8_t const z = 0;
					std::fill(mInfo, mInfo + calcNumBytesInfo(numElementsWithBuffer), z);
					mInfo[numElementsWithBuffer] = 1;

					mInfoInc = InitialInfoInc;
					mInfoHashShift = InitialInfoHashShift;
				}

				// Destroys the map and all it's contents.
				~Table() {
					ROBIN_HOOD_TRACE(this)
						destroy();
				}

				// Checks if both tables contain the same entries. Order is irrelevant.
				bool operator==(const Table& other) const {
					ROBIN_HOOD_TRACE(this)
						if (other.size() != size()) {
							return false;
						}
					for (auto const& otherEntry : other) {
						if (!has(otherEntry)) {
							return false;
						}
					}

					return true;
				}

				bool operator!=(const Table& other) const {
					ROBIN_HOOD_TRACE(this)
						return !operator==(other);
				}

				template <typename Q = mapped_type>
				typename std::enable_if<!std::is_void<Q>::value, Q&>::type operator[](const key_type& key) {
					ROBIN_HOOD_TRACE(this)
						return doCreateByKey(key);
				}

				template <typename Q = mapped_type>
				typename std::enable_if<!std::is_void<Q>::value, Q&>::type operator[](key_type&& key) {
					ROBIN_HOOD_TRACE(this)
						return doCreateByKey(std::move(key));
				}

				template <typename Iter>
				void insert(Iter first, Iter last) {
					for (; first != last; ++first) {
						// value_type ctor needed because this might be called with std::pair's
						insert(value_type(*first));
					}
				}

				template <typename... Args>
				std::pair<iterator, bool> emplace(Args&&... args) {
					ROBIN_HOOD_TRACE(this)
						Node n {
						*this, std::forward<Args>(args)...
					};
					auto r = doInsert(std::move(n));
					if (!r.second) {
						// insertion not possible: destroy node
						// NOLINTNEXTLINE(bugprone-use-after-move)
						n.destroy(*this);
					}
					return r;
				}

				template <typename... Args>
				std::pair<iterator, bool> try_emplace(const key_type& key, Args&&... args) {
					return try_emplace_impl(key, std::forward<Args>(args)...);
				}

				template <typename... Args>
				std::pair<iterator, bool> try_emplace(key_type&& key, Args&&... args) {
					return try_emplace_impl(std::move(key), std::forward<Args>(args)...);
				}

				template <typename... Args>
				std::pair<iterator, bool> try_emplace(const_iterator hint, const key_type& key,
					Args&&... args) {
					(void)hint;
					return try_emplace_impl(key, std::forward<Args>(args)...);
				}

				template <typename... Args>
				std::pair<iterator, bool> try_emplace(const_iterator hint, key_type&& key, Args&&... args) {
					(void)hint;
					return try_emplace_impl(std::move(key), std::forward<Args>(args)...);
				}

				template <typename Mapped>
				std::pair<iterator, bool> insert_or_assign(const key_type& key, Mapped&& obj) {
					return insert_or_assign_impl(key, std::forward<Mapped>(obj));
				}

				template <typename Mapped>
				std::pair<iterator, bool> insert_or_assign(key_type&& key, Mapped&& obj) {
					return insert_or_assign_impl(std::move(key), std::forward<Mapped>(obj));
				}

				template <typename Mapped>
				std::pair<iterator, bool> insert_or_assign(const_iterator hint, const key_type& key,
					Mapped&& obj) {
					(void)hint;
					return insert_or_assign_impl(key, std::forward<Mapped>(obj));
				}

				template <typename Mapped>
				std::pair<iterator, bool> insert_or_assign(const_iterator hint, key_type&& key, Mapped&& obj) {
					(void)hint;
					return insert_or_assign_impl(std::move(key), std::forward<Mapped>(obj));
				}

				std::pair<iterator, bool> insert(const value_type& keyval) {
					ROBIN_HOOD_TRACE(this)
						return doInsert(keyval);
				}

				std::pair<iterator, bool> insert(value_type&& keyval) {
					return doInsert(std::move(keyval));
				}

				// Returns 1 if key is found, 0 otherwise.
				size_t count(const key_type& key) const { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						auto kv = mKeyVals + findIdx(key);
					if (kv != reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
						return 1;
					}
					return 0;
				}

				template <typename OtherKey, typename Self_ = Self>
				// NOLINTNEXTLINE(modernize-use-nodiscard)
				typename std::enable_if<Self_::is_transparent, size_t>::type count(const OtherKey& key) const {
					ROBIN_HOOD_TRACE(this)
						auto kv = mKeyVals + findIdx(key);
					if (kv != reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
						return 1;
					}
					return 0;
				}

				bool contains(const key_type& key) const { // NOLINT(modernize-use-nodiscard)
					return 1U == count(key);
				}

				template <typename OtherKey, typename Self_ = Self>
				// NOLINTNEXTLINE(modernize-use-nodiscard)
				typename std::enable_if<Self_::is_transparent, bool>::type contains(const OtherKey& key) const {
					return 1U == count(key);
				}

				// Returns a reference to the value found for key.
				// Throws std::out_of_range if element cannot be found
				template <typename Q = mapped_type>
				// NOLINTNEXTLINE(modernize-use-nodiscard)
				typename std::enable_if<!std::is_void<Q>::value, Q&>::type at(key_type const& key) {
					ROBIN_HOOD_TRACE(this)
						auto kv = mKeyVals + findIdx(key);
					if (kv == reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
						doThrow<std::out_of_range>("key not found");
					}
					return kv->getSecond();
				}

				// Returns a reference to the value found for key.
				// Throws std::out_of_range if element cannot be found
				template <typename Q = mapped_type>
				// NOLINTNEXTLINE(modernize-use-nodiscard)
				typename std::enable_if<!std::is_void<Q>::value, Q const&>::type at(key_type const& key) const {
					ROBIN_HOOD_TRACE(this)
						auto kv = mKeyVals + findIdx(key);
					if (kv == reinterpret_cast_no_cast_align_warning<Node*>(mInfo)) {
						doThrow<std::out_of_range>("key not found");
					}
					return kv->getSecond();
				}

				const_iterator find(const key_type& key) const { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						const size_t idx = findIdx(key);
					return const_iterator{ mKeyVals + idx, mInfo + idx };
				}

				template <typename OtherKey>
				const_iterator find(const OtherKey& key, is_transparent_tag /*unused*/) const {
					ROBIN_HOOD_TRACE(this)
						const size_t idx = findIdx(key);
					return const_iterator{ mKeyVals + idx, mInfo + idx };
				}

				template <typename OtherKey, typename Self_ = Self>
				typename std::enable_if<Self_::is_transparent, // NOLINT(modernize-use-nodiscard)
					const_iterator>::type  // NOLINT(modernize-use-nodiscard)
					find(const OtherKey& key) const {              // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						const size_t idx = findIdx(key);
					return const_iterator{ mKeyVals + idx, mInfo + idx };
				}

				iterator find(const key_type& key) {
					ROBIN_HOOD_TRACE(this)
						const size_t idx = findIdx(key);
					return iterator{ mKeyVals + idx, mInfo + idx };
				}

				template <typename OtherKey>
				iterator find(const OtherKey& key, is_transparent_tag /*unused*/) {
					ROBIN_HOOD_TRACE(this)
						const size_t idx = findIdx(key);
					return iterator{ mKeyVals + idx, mInfo + idx };
				}

				template <typename OtherKey, typename Self_ = Self>
				typename std::enable_if<Self_::is_transparent, iterator>::type find(const OtherKey& key) {
					ROBIN_HOOD_TRACE(this)
						const size_t idx = findIdx(key);
					return iterator{ mKeyVals + idx, mInfo + idx };
				}

				iterator begin() {
					ROBIN_HOOD_TRACE(this)
						if (empty()) {
							return end();
						}
					return iterator(mKeyVals, mInfo, fast_forward_tag{});
				}
				const_iterator begin() const { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						return cbegin();
				}
				const_iterator cbegin() const { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						if (empty()) {
							return cend();
						}
					return const_iterator(mKeyVals, mInfo, fast_forward_tag{});
				}

				iterator end() {
					ROBIN_HOOD_TRACE(this)
						// no need to supply valid info pointer: end() must not be dereferenced, and only node
						// pointer is compared.
						return iterator{ reinterpret_cast_no_cast_align_warning<Node*>(mInfo), nullptr };
				}
				const_iterator end() const { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						return cend();
				}
				const_iterator cend() const { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						return const_iterator{ reinterpret_cast_no_cast_align_warning<Node*>(mInfo), nullptr };
				}

				iterator erase(const_iterator pos) {
					ROBIN_HOOD_TRACE(this)
						// its safe to perform const cast here
						// NOLINTNEXTLINE(cppcoreguidelines-pro-type-const-cast)
						return erase(iterator{ const_cast<Node*>(pos.mKeyVals), const_cast<uint8_t*>(pos.mInfo) });
				}

				// Erases element at pos, returns iterator to the next element.
				iterator erase(iterator pos) {
					ROBIN_HOOD_TRACE(this)
						// we assume that pos always points to a valid entry, and not end().
						auto const idx = static_cast<size_t>(pos.mKeyVals - mKeyVals);

					shiftDown(idx);
					--mNumElements;

					if (*pos.mInfo) {
						// we've backward shifted, return this again
						return pos;
					}

					// no backward shift, return next element
					return ++pos;
				}

				size_t erase(const key_type& key) {
					ROBIN_HOOD_TRACE(this)
						size_t idx {};
					InfoType info{};
					keyToIdx(key, &idx, &info);

					// check while info matches with the source idx
					do {
						if (info == mInfo[idx] && WKeyEqual::operator()(key, mKeyVals[idx].getFirst())) {
							shiftDown(idx);
							--mNumElements;
							return 1;
						}
						next(&info, &idx);
					} while (info <= mInfo[idx]);

					// nothing found to delete
					return 0;
				}

				// reserves space for the specified number of elements. Makes sure the old data fits.
				// exactly the same as reserve(c).
				void rehash(size_t c) {
					// forces a reserve
					reserve(c, true);
				}

				// reserves space for the specified number of elements. Makes sure the old data fits.
				// Exactly the same as rehash(c). Use rehash(0) to shrink to fit.
				void reserve(size_t c) {
					// reserve, but don't force rehash
					reserve(c, false);
				}

				// If possible reallocates the map to a smaller one. This frees the underlying table.
				// Does not do anything if load_factor is too large for decreasing the table's size.
				void compact() {
					ROBIN_HOOD_TRACE(this)
						auto newSize = InitialNumElements;
					while (calcMaxNumElementsAllowed(newSize) < mNumElements && newSize != 0) {
						newSize *= 2;
					}
					if (ROBIN_HOOD_UNLIKELY(newSize == 0)) {
						throwOverflowError();
					}

					ROBIN_HOOD_LOG("newSize > mMask + 1: " << newSize << " > " << mMask << " + 1")

						// only actually do anything when the new size is bigger than the old one. This prevents to
						// continuously allocate for each reserve() call.
						if (newSize < mMask + 1) {
							rehashPowerOfTwo(newSize, true);
						}
				}

				size_type size() const noexcept { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						return mNumElements;
				}

				size_type max_size() const noexcept { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						return static_cast<size_type>(-1);
				}

				ROBIN_HOOD(NODISCARD) bool empty() const noexcept {
					ROBIN_HOOD_TRACE(this)
						return 0 == mNumElements;
				}

				float max_load_factor() const noexcept { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						return MaxLoadFactor100 / 100.0F;
				}

				// Average number of elements per bucket. Since we allow only 1 per bucket
				float load_factor() const noexcept { // NOLINT(modernize-use-nodiscard)
					ROBIN_HOOD_TRACE(this)
						return static_cast<float>(size()) / static_cast<float>(mMask + 1);
				}

				ROBIN_HOOD(NODISCARD) size_t mask() const noexcept {
					ROBIN_HOOD_TRACE(this)
						return mMask;
				}

				ROBIN_HOOD(NODISCARD) size_t calcMaxNumElementsAllowed(size_t maxElements) const noexcept {
					if (ROBIN_HOOD_LIKELY(maxElements <= (std::numeric_limits<size_t>::max)() / 100)) {
						return maxElements * MaxLoadFactor100 / 100;
					}

					// we might be a bit inprecise, but since maxElements is quite large that doesn't matter
					return (maxElements / 100) * MaxLoadFactor100;
				}

				ROBIN_HOOD(NODISCARD) size_t calcNumBytesInfo(size_t numElements) const noexcept {
					// we add a uint64_t, which houses the sentinel (first byte) and padding so we can load
					// 64bit types.
					return numElements + sizeof(uint64_t);
				}

				ROBIN_HOOD(NODISCARD)
					size_t calcNumElementsWithBuffer(size_t numElements) const noexcept {
					auto maxNumElementsAllowed = calcMaxNumElementsAllowed(numElements);
					return numElements + (std::min)(maxNumElementsAllowed, (static_cast<size_t>(0xFF)));
				}

				// calculation only allowed for 2^n values
				ROBIN_HOOD(NODISCARD) size_t calcNumBytesTotal(size_t numElements) const {
#if ROBIN_HOOD(BITNESS) == 64
					return numElements * sizeof(Node) + calcNumBytesInfo(numElements);
#else
					// make sure we're doing 64bit operations, so we are at least safe against 32bit overflows.
					auto const ne = static_cast<uint64_t>(numElements);
					auto const s = static_cast<uint64_t>(sizeof(Node));
					auto const infos = static_cast<uint64_t>(calcNumBytesInfo(numElements));

					auto const total64 = ne * s + infos;
					auto const total = static_cast<size_t>(total64);

					if (ROBIN_HOOD_UNLIKELY(static_cast<uint64_t>(total) != total64)) {
						throwOverflowError();
					}
					return total;
#endif
				}

			private:
				template <typename Q = mapped_type>
				ROBIN_HOOD(NODISCARD)
					typename std::enable_if<!std::is_void<Q>::value, bool>::type has(const value_type& e) const {
					ROBIN_HOOD_TRACE(this)
						auto it = find(e.first);
					return it != end() && it->second == e.second;
				}

				template <typename Q = mapped_type>
				ROBIN_HOOD(NODISCARD)
					typename std::enable_if<std::is_void<Q>::value, bool>::type has(const value_type& e) const {
					ROBIN_HOOD_TRACE(this)
						return find(e) != end();
				}

				void reserve(size_t c, bool forceRehash) {
					ROBIN_HOOD_TRACE(this)
						auto const minElementsAllowed = (std::max)(c, mNumElements);
					auto newSize = InitialNumElements;
					while (calcMaxNumElementsAllowed(newSize) < minElementsAllowed && newSize != 0) {
						newSize *= 2;
					}
					if (ROBIN_HOOD_UNLIKELY(newSize == 0)) {
						throwOverflowError();
					}

					ROBIN_HOOD_LOG("newSize > mMask + 1: " << newSize << " > " << mMask << " + 1")

						// only actually do anything when the new size is bigger than the old one. This prevents to
						// continuously allocate for each reserve() call.
						if (forceRehash || newSize > mMask + 1) {
							rehashPowerOfTwo(newSize, false);
						}
				}

				// reserves space for at least the specified number of elements.
				// only works if numBuckets if power of two
				void rehashPowerOfTwo(size_t numBuckets, bool forceFree) {
					ROBIN_HOOD_TRACE(this)

						Node* const oldKeyVals = mKeyVals;
					uint8_t const* const oldInfo = mInfo;

					const size_t oldMaxElementsWithBuffer = calcNumElementsWithBuffer(mMask + 1);

					// resize operation: move stuff
					init_data(numBuckets);
					if (oldMaxElementsWithBuffer > 1) {
						for (size_t i = 0; i < oldMaxElementsWithBuffer; ++i) {
							if (oldInfo[i] != 0) {
								insert_move(std::move(oldKeyVals[i]));
								// destroy the node but DON'T destroy the data.
								oldKeyVals[i].~Node();
							}
						}

						// this check is not necessary as it's guarded by the previous if, but it helps silence
						// g++'s overeager "attempt to free a non-heap object 'map'
						// [-Werror=free-nonheap-object]" warning.
						if (oldKeyVals != reinterpret_cast_no_cast_align_warning<Node*>(&mMask)) {
							// don't destroy old data: put it into the pool instead
							if (forceFree) {
								std::free(oldKeyVals);
							}
							else {
								DataPool::addOrFree(oldKeyVals, calcNumBytesTotal(oldMaxElementsWithBuffer));
							}
						}
					}
				}

				ROBIN_HOOD(NOINLINE) void throwOverflowError() const {
#if ROBIN_HOOD(HAS_EXCEPTIONS)
					throw std::overflow_error("robin_hood::map overflow");
#else
					abort();
#endif
				}

				template <typename OtherKey, typename... Args>
				std::pair<iterator, bool> try_emplace_impl(OtherKey&& key, Args&&... args) {
					ROBIN_HOOD_TRACE(this)
						auto it = find(key);
					if (it == end()) {
						return emplace(std::piecewise_construct,
							std::forward_as_tuple(std::forward<OtherKey>(key)),
							std::forward_as_tuple(std::forward<Args>(args)...));
					}
					return { it, false };
				}

				template <typename OtherKey, typename Mapped>
				std::pair<iterator, bool> insert_or_assign_impl(OtherKey&& key, Mapped&& obj) {
					ROBIN_HOOD_TRACE(this)
						auto it = find(key);
					if (it == end()) {
						return emplace(std::forward<OtherKey>(key), std::forward<Mapped>(obj));
					}
					it->second = std::forward<Mapped>(obj);
					return { it, false };
				}

				void init_data(size_t max_elements) {
					mNumElements = 0;
					mMask = max_elements - 1;
					mMaxNumElementsAllowed = calcMaxNumElementsAllowed(max_elements);

					auto const numElementsWithBuffer = calcNumElementsWithBuffer(max_elements);

					// calloc also zeroes everything
					auto const numBytesTotal = calcNumBytesTotal(numElementsWithBuffer);
					ROBIN_HOOD_LOG("std::calloc " << numBytesTotal << " = calcNumBytesTotal("
						<< numElementsWithBuffer << ")")
						mKeyVals = reinterpret_cast<Node*>(
							detail::assertNotNull<std::bad_alloc>(std::calloc(1, numBytesTotal)));
					mInfo = reinterpret_cast<uint8_t*>(mKeyVals + numElementsWithBuffer);

					// set sentinel
					mInfo[numElementsWithBuffer] = 1;

					mInfoInc = InitialInfoInc;
					mInfoHashShift = InitialInfoHashShift;
				}

				template <typename Arg, typename Q = mapped_type>
				typename std::enable_if<!std::is_void<Q>::value, Q&>::type doCreateByKey(Arg&& key) {
					while (true) {
						size_t idx{};
						InfoType info{};
						keyToIdx(key, &idx, &info);
						nextWhileLess(&info, &idx);

						// while we potentially have a match. Can't do a do-while here because when mInfo is
						// 0 we don't want to skip forward
						while (info == mInfo[idx]) {
							if (WKeyEqual::operator()(key, mKeyVals[idx].getFirst())) {
								// key already exists, do not insert.
								return mKeyVals[idx].getSecond();
							}
							next(&info, &idx);
						}

						// unlikely that this evaluates to true
						if (ROBIN_HOOD_UNLIKELY(mNumElements >= mMaxNumElementsAllowed)) {
							increase_size();
							continue;
						}

						// key not found, so we are now exactly where we want to insert it.
						auto const insertion_idx = idx;
						auto const insertion_info = info;
						if (ROBIN_HOOD_UNLIKELY(insertion_info + mInfoInc > 0xFF)) {
							mMaxNumElementsAllowed = 0;
						}

						// find an empty spot
						while (0 != mInfo[idx]) {
							next(&info, &idx);
						}

						auto& l = mKeyVals[insertion_idx];
						if (idx == insertion_idx) {
							// put at empty spot. This forwards all arguments into the node where the object
							// is constructed exactly where it is needed.
							::new (static_cast<void*>(&l))
								Node(*this, std::piecewise_construct,
									std::forward_as_tuple(std::forward<Arg>(key)), std::forward_as_tuple());
						}
						else {
							shiftUp(idx, insertion_idx);
							l = Node(*this, std::piecewise_construct,
								std::forward_as_tuple(std::forward<Arg>(key)), std::forward_as_tuple());
						}

						// mKeyVals[idx].getFirst() = std::move(key);
						mInfo[insertion_idx] = static_cast<uint8_t>(insertion_info);

						++mNumElements;
						return mKeyVals[insertion_idx].getSecond();
					}
				}

				// This is exactly the same code as operator[], except for the return values
				template <typename Arg>
				std::pair<iterator, bool> doInsert(Arg&& keyval) {
					while (true) {
						size_t idx{};
						InfoType info{};
						keyToIdx(getFirstConst(keyval), &idx, &info);
						nextWhileLess(&info, &idx);

						// while we potentially have a match
						while (info == mInfo[idx]) {
							if (WKeyEqual::operator()(getFirstConst(keyval), mKeyVals[idx].getFirst())) {
								// key already exists, do NOT insert.
								// see http://en.cppreference.com/w/cpp/container/unordered_map/insert
								return std::make_pair<iterator, bool>(iterator(mKeyVals + idx, mInfo + idx),
									false);
							}
							next(&info, &idx);
						}

						// unlikely that this evaluates to true
						if (ROBIN_HOOD_UNLIKELY(mNumElements >= mMaxNumElementsAllowed)) {
							increase_size();
							continue;
						}

						// key not found, so we are now exactly where we want to insert it.
						auto const insertion_idx = idx;
						auto const insertion_info = info;
						if (ROBIN_HOOD_UNLIKELY(insertion_info + mInfoInc > 0xFF)) {
							mMaxNumElementsAllowed = 0;
						}

						// find an empty spot
						while (0 != mInfo[idx]) {
							next(&info, &idx);
						}

						auto& l = mKeyVals[insertion_idx];
						if (idx == insertion_idx) {
							::new (static_cast<void*>(&l)) Node(*this, std::forward<Arg>(keyval));
						}
						else {
							shiftUp(idx, insertion_idx);
							l = Node(*this, std::forward<Arg>(keyval));
						}

						// put at empty spot
						mInfo[insertion_idx] = static_cast<uint8_t>(insertion_info);

						++mNumElements;
						return std::make_pair(iterator(mKeyVals + insertion_idx, mInfo + insertion_idx), true);
					}
				}

				bool try_increase_info() {
					ROBIN_HOOD_LOG("mInfoInc=" << mInfoInc << ", numElements=" << mNumElements
						<< ", maxNumElementsAllowed="
						<< calcMaxNumElementsAllowed(mMask + 1))
						if (mInfoInc <= 2) {
							// need to be > 2 so that shift works (otherwise undefined behavior!)
							return false;
						}
					// we got space left, try to make info smaller
					mInfoInc = static_cast<uint8_t>(mInfoInc >> 1U);

					// remove one bit of the hash, leaving more space for the distance info.
					// This is extremely fast because we can operate on 8 bytes at once.
					++mInfoHashShift;
					auto const numElementsWithBuffer = calcNumElementsWithBuffer(mMask + 1);

					for (size_t i = 0; i < numElementsWithBuffer; i += 8) {
						auto val = unaligned_load<uint64_t>(mInfo + i);
						val = (val >> 1U) & UINT64_C(0x7f7f7f7f7f7f7f7f);
						std::memcpy(mInfo + i, &val, sizeof(val));
					}
					// update sentinel, which might have been cleared out!
					mInfo[numElementsWithBuffer] = 1;

					mMaxNumElementsAllowed = calcMaxNumElementsAllowed(mMask + 1);
					return true;
				}

				void increase_size() {
					// nothing allocated yet? just allocate InitialNumElements
					if (0 == mMask) {
						init_data(InitialNumElements);
						return;
					}

					auto const maxNumElementsAllowed = calcMaxNumElementsAllowed(mMask + 1);
					if (mNumElements < maxNumElementsAllowed && try_increase_info()) {
						return;
					}

					ROBIN_HOOD_LOG("mNumElements=" << mNumElements << ", maxNumElementsAllowed="
						<< maxNumElementsAllowed << ", load="
						<< (static_cast<double>(mNumElements) * 100.0 /
							(static_cast<double>(mMask) + 1)))
						// it seems we have a really bad hash function! don't try to resize again
						if (mNumElements * 2 < calcMaxNumElementsAllowed(mMask + 1)) {
							throwOverflowError();
						}

					rehashPowerOfTwo((mMask + 1) * 2, false);
				}

				void destroy() {
					if (0 == mMask) {
						// don't deallocate!
						return;
					}

					Destroyer<Self, IsFlat&& std::is_trivially_destructible<Node>::value>{}
					.nodesDoNotDeallocate(*this);

					// This protection against not deleting mMask shouldn't be needed as it's sufficiently
					// protected with the 0==mMask check, but I have this anyways because g++ 7 otherwise
					// reports a compile error: attempt to free a non-heap object 'fm'
					// [-Werror=free-nonheap-object]
					if (mKeyVals != reinterpret_cast_no_cast_align_warning<Node*>(&mMask)) {
						ROBIN_HOOD_LOG("std::free")
							std::free(mKeyVals);
					}
				}

				void init() noexcept {
					mKeyVals = reinterpret_cast_no_cast_align_warning<Node*>(&mMask);
					mInfo = reinterpret_cast<uint8_t*>(&mMask);
					mNumElements = 0;
					mMask = 0;
					mMaxNumElementsAllowed = 0;
					mInfoInc = InitialInfoInc;
					mInfoHashShift = InitialInfoHashShift;
				}

				// members are sorted so no padding occurs
				Node* mKeyVals = reinterpret_cast_no_cast_align_warning<Node*>(&mMask); // 8 byte  8
				uint8_t* mInfo = reinterpret_cast<uint8_t*>(&mMask);                    // 8 byte 16
				size_t mNumElements = 0;                                                // 8 byte 24
				size_t mMask = 0;                                                       // 8 byte 32
				size_t mMaxNumElementsAllowed = 0;                                      // 8 byte 40
				InfoType mInfoInc = InitialInfoInc;                                     // 4 byte 44
				InfoType mInfoHashShift = InitialInfoHashShift;                         // 4 byte 48
																// 16 byte 56 if NodeAllocator
		};

	} // namespace detail

	// map

	template <typename Key, typename T, typename Hash = hash<Key>,
		typename KeyEqual = std::equal_to<Key>, size_t MaxLoadFactor100 = 80>
		using unordered_flat_map = detail::Table<true, MaxLoadFactor100, Key, T, Hash, KeyEqual>;

	template <typename Key, typename T, typename Hash = hash<Key>,
		typename KeyEqual = std::equal_to<Key>, size_t MaxLoadFactor100 = 80>
		using unordered_node_map = detail::Table<false, MaxLoadFactor100, Key, T, Hash, KeyEqual>;

	template <typename Key, typename T, typename Hash = hash<Key>,
		typename KeyEqual = std::equal_to<Key>, size_t MaxLoadFactor100 = 80>
		using unordered_map =
		detail::Table<sizeof(robin_hood::pair<Key, T>) <= sizeof(size_t) * 6 &&
		std::is_nothrow_move_constructible<robin_hood::pair<Key, T>>::value &&
		std::is_nothrow_move_assignable<robin_hood::pair<Key, T>>::value,
		MaxLoadFactor100, Key, T, Hash, KeyEqual>;

	// set

	template <typename Key, typename Hash = hash<Key>, typename KeyEqual = std::equal_to<Key>,
		size_t MaxLoadFactor100 = 80>
		using unordered_flat_set = detail::Table<true, MaxLoadFactor100, Key, void, Hash, KeyEqual>;

	template <typename Key, typename Hash = hash<Key>, typename KeyEqual = std::equal_to<Key>,
		size_t MaxLoadFactor100 = 80>
		using unordered_node_set = detail::Table<false, MaxLoadFactor100, Key, void, Hash, KeyEqual>;

	template <typename Key, typename Hash = hash<Key>, typename KeyEqual = std::equal_to<Key>,
		size_t MaxLoadFactor100 = 80>
		using unordered_set = detail::Table<sizeof(Key) <= sizeof(size_t) * 6 &&
		std::is_nothrow_move_constructible<Key>::value &&
		std::is_nothrow_move_assignable<Key>::value,
		MaxLoadFactor100, Key, void, Hash, KeyEqual>;

} // namespace robin_hood

#endif
