poco/Foundation/include/Poco/ordered_hash.h

/**
 * MIT License
 *
 * Copyright (c) 2017 Tessil
 *
 * 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 TSL_ORDERED_HASH_H
#define TSL_ORDERED_HASH_H


#include <algorithm>
#include <cassert>
#include <climits>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <iterator>
#include <limits>
#include <memory>
#include <stdexcept>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>


/**
 * Macros for compatibility with GCC 4.8
 */
#ifndef TSL_NO_CONTAINER_ERASE_CONST_ITERATOR
    #if (defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ < 9))
    #define TSL_NO_CONTAINER_ERASE_CONST_ITERATOR
    #endif
#endif

#ifndef TSL_NO_CONTAINER_EMPLACE_CONST_ITERATOR
    #if (defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ < 9))
    #define TSL_NO_CONTAINER_EMPLACE_CONST_ITERATOR
    #endif
#endif


/*
 * Only activate tsl_assert if TSL_DEBUG is defined.
 * This way we avoid the performance hit when NDEBUG is not defined with assert as tsl_assert is used a lot
 * (people usually compile with "-O3" and not "-O3 -DNDEBUG").
 */
#ifndef tsl_assert
    #ifdef TSL_DEBUG
    #define tsl_assert(expr) assert(expr)
    #else
    #define tsl_assert(expr) (static_cast<void>(0))
    #endif
#endif


namespace tsl {

namespace detail_ordered_hash {

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

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

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


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

template<typename T>
struct is_vector<T, typename std::enable_if<
                        std::is_same<T, std::vector<typename T::value_type, typename T::allocator_type>>::value
                    >::type>: std::true_type {
};


/**
 * Each bucket entry stores a 32-bits index which is the index in m_values corresponding to the bucket's value
 * and a 32 bits hash (truncated if the original was 64-bits) corresponding to the hash of the value.
 *
 * The 32-bit index limits the size of the map to 2^32 - 1 elements (-1 due to a reserved value used to mark a
 * bucket as empty).
 */
class bucket_entry {
public:
    using index_type = std::uint_least32_t;
    using truncated_hash_type = std::uint_least32_t;


    bucket_entry() noexcept: m_index(EMPTY_MARKER_INDEX), m_hash(0) {
    }

    bool empty() const noexcept {
        return m_index == EMPTY_MARKER_INDEX;
    }

    void clear() noexcept {
        m_index = EMPTY_MARKER_INDEX;
    }

    index_type index() const noexcept {
        tsl_assert(!empty());
        return m_index;
    }

    index_type& index_ref() noexcept {
        tsl_assert(!empty());
        return m_index;
    }

    void set_index(index_type index) noexcept {
        tsl_assert(index <= max_size());

        m_index = index;
    }

    truncated_hash_type truncated_hash() const noexcept {
        tsl_assert(!empty());
        return m_hash;
    }

    truncated_hash_type& truncated_hash_ref() noexcept {
        tsl_assert(!empty());
        return m_hash;
    }

    void set_hash(std::size_t hash) noexcept {
        m_hash = truncate_hash(hash);
    }



    static truncated_hash_type truncate_hash(std::size_t hash) noexcept {
        return truncated_hash_type(hash);
    }

    static std::size_t max_size() noexcept {
        return std::numeric_limits<index_type>::max() - NB_RESERVED_INDEXES;
    }

private:
    static const index_type EMPTY_MARKER_INDEX = std::numeric_limits<index_type>::max();
    static const std::size_t NB_RESERVED_INDEXES = 1;

    index_type m_index;
    truncated_hash_type m_hash;
};



/**
 * Internal common class used by ordered_map and ordered_set.
 *
 * ValueType is what will be stored by ordered_hash (usually std::pair<Key, T> for map and Key for set).
 *
 * KeySelect should be a FunctionObject which takes a ValueType in parameter and return a reference to the key.
 *
 * ValueSelect should be a FunctionObject which takes a ValueType in parameter and return a reference to the value.
 * ValueSelect should be void if there is no value (in set for example).
 *
 * ValueTypeContainer is the container which will be used to store ValueType values.
 * Usually a std::deque<ValueType, Allocator> or std::vector<ValueType, Allocator>.
 *
 *
 *
 * The orderd_hash structure is a hash table which preserves the order of insertion of the elements.
 * To do so, it stores the values in the ValueTypeContainer (m_values) using emplace_back at each
 * insertion of a new element. Another structure (m_buckets of type std::vector<bucket_entry>) will
 * serve as buckets array for the hash table part. Each bucket stores an index which corresponds to
 * the index in m_values where the bucket's value is and the (truncated) hash of this value. An index
 * is used instead of a pointer to the value to reduce the size of each bucket entry.
 *
 * To resolve collisions in the buckets array, the structures use robin hood linear probing with
 * backward shift deletion.
 */
template<class ValueType,
         class KeySelect,
         class ValueSelect,
         class Hash,
         class KeyEqual,
         class Allocator,
         class ValueTypeContainer>
class ordered_hash: private Hash, private KeyEqual {
private:
    template<typename U>
    using has_mapped_type = typename std::integral_constant<bool, !std::is_same<U, void>::value>;

    static_assert(std::is_same<typename ValueTypeContainer::value_type, ValueType>::value,
                  "ValueTypeContainer::value_type != ValueType.");
    static_assert(std::is_same<typename ValueTypeContainer::allocator_type, Allocator>::value,
                  "ValueTypeContainer::allocator_type != Allocator.");


public:
    template<bool IsConst>
    class ordered_iterator;

    using key_type = typename KeySelect::key_type;
    using value_type = ValueType;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;
    using hasher = Hash;
    using key_equal = KeyEqual;
    using allocator_type = Allocator;
    using reference = value_type&;
    using const_reference = const value_type&;
    using pointer = value_type*;
    using const_pointer = const value_type*;
    using iterator = ordered_iterator<false>;
    using const_iterator = ordered_iterator<true>;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    using values_container_type = ValueTypeContainer;

public:
    template<bool IsConst>
    class ordered_iterator {
        friend class ordered_hash;

    private:
        using iterator = typename std::conditional<IsConst,
                                                    typename values_container_type::const_iterator,
                                                    typename values_container_type::iterator>::type;


        ordered_iterator(iterator it) noexcept: m_iterator(it) {
        }

    public:
        using iterator_category = std::random_access_iterator_tag;
        using value_type = const typename ordered_hash::value_type;
        using difference_type = typename iterator::difference_type;
        using reference = value_type&;
        using pointer = value_type*;


        ordered_iterator() noexcept {
        }

        ordered_iterator(const ordered_iterator<false>& other) noexcept: m_iterator(other.m_iterator) {
        }

        const typename ordered_hash::key_type& key() const {
            return KeySelect()(*m_iterator);
        }

        template<class U = ValueSelect, typename std::enable_if<has_mapped_type<U>::value && IsConst>::type* = nullptr>
        const typename U::value_type& value() const {
            return U()(*m_iterator);
        }

        template<class U = ValueSelect, typename std::enable_if<has_mapped_type<U>::value && !IsConst>::type* = nullptr>
        typename U::value_type& value() {
            return U()(*m_iterator);
        }

        reference operator*() const { return *m_iterator; }
        pointer operator->() const { return m_iterator.operator->(); }

        ordered_iterator& operator++() { ++m_iterator; return *this; }
        ordered_iterator& operator--() { --m_iterator; return *this; }

        ordered_iterator operator++(int) { ordered_iterator tmp(*this); ++(*this); return tmp; }
        ordered_iterator operator--(int) { ordered_iterator tmp(*this); --(*this); return tmp; }

        reference operator[](difference_type n) const { return m_iterator[n]; }

        ordered_iterator& operator+=(difference_type n) { m_iterator += n; return *this; }
        ordered_iterator& operator-=(difference_type n) { m_iterator -= n; return *this; }

        ordered_iterator operator+(difference_type n) { ordered_iterator tmp(*this); tmp += n; return tmp; }
        ordered_iterator operator-(difference_type n) { ordered_iterator tmp(*this); tmp -= n; return tmp; }

        friend bool operator==(const ordered_iterator& lhs, const ordered_iterator& rhs) {
            return lhs.m_iterator == rhs.m_iterator;
        }

        friend bool operator!=(const ordered_iterator& lhs, const ordered_iterator& rhs) {
            return lhs.m_iterator != rhs.m_iterator;
        }

        friend bool operator<(const ordered_iterator& lhs, const ordered_iterator& rhs) {
            return lhs.m_iterator < rhs.m_iterator;
        }

        friend bool operator>(const ordered_iterator& lhs, const ordered_iterator& rhs) {
            return lhs.m_iterator > rhs.m_iterator;
        }

        friend bool operator<=(const ordered_iterator& lhs, const ordered_iterator& rhs) {
            return lhs.m_iterator <= rhs.m_iterator;
        }

        friend bool operator>=(const ordered_iterator& lhs, const ordered_iterator& rhs) {
            return lhs.m_iterator >= rhs.m_iterator;
        }

        friend ordered_iterator operator+(difference_type n, const ordered_iterator& it) {
            return n + it.m_iterator;
        }

        friend difference_type operator-(const ordered_iterator& lhs, const ordered_iterator& rhs) {
            return lhs.m_iterator - rhs.m_iterator;
        }

    private:
        iterator m_iterator;
    };


private:
    using buckets_container_allocator = typename
                            std::allocator_traits<allocator_type>::template rebind_alloc<bucket_entry>;

    using buckets_container_type = std::vector<bucket_entry, buckets_container_allocator>;


    using truncated_hash_type = typename bucket_entry::truncated_hash_type;
    using index_type = typename bucket_entry::index_type;

public:
    ordered_hash(size_type bucket_count,
                 const Hash& hash,
                 const KeyEqual& equal,
                 const Allocator& alloc,
                 float max_load_factor): Hash(hash), KeyEqual(equal), m_buckets(alloc),
                                         m_values(alloc), m_grow_on_next_insert(false)
    {
        bucket_count = round_up_to_power_of_two(bucket_count);
        if(bucket_count > max_bucket_count()) {
            throw std::length_error("The map exceeds its maxmimum size.");
        }
        tsl_assert(bucket_count > 0);

        m_buckets.resize(bucket_count);
        m_mask = bucket_count - 1;

        this->max_load_factor(max_load_factor);
    }

    allocator_type get_allocator() const {
        return m_values.get_allocator();
    }


    /*
     * Iterators
     */
    iterator begin() noexcept {
        return iterator(m_values.begin());
    }

    const_iterator begin() const noexcept {
        return cbegin();
    }

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

    iterator end() noexcept {
        return iterator(m_values.end());
    }

    const_iterator end() const noexcept {
        return cend();
    }

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


    reverse_iterator rbegin() noexcept {
        return reverse_iterator(m_values.end());
    }

    const_reverse_iterator rbegin() const noexcept {
        return rcbegin();
    }

    const_reverse_iterator rcbegin() const noexcept {
        return const_reverse_iterator(m_values.cend());
    }

    reverse_iterator rend() noexcept {
        return reverse_iterator(m_values.begin());
    }

    const_reverse_iterator rend() const noexcept {
        return rcend();
    }

    const_reverse_iterator rcend() const noexcept {
        return const_reverse_iterator(m_values.cbegin());
    }


    /*
     * Capacity
     */
    bool empty() const noexcept {
        return m_values.empty();
    }

    size_type size() const noexcept {
        return m_values.size();
    }

    size_type max_size() const noexcept {
        return std::min(bucket_entry::max_size(), m_values.max_size());
    }


    /*
     * Modifiers
     */
    void clear() noexcept {
        for(auto& bucket: m_buckets) {
            bucket.clear();
        }

        m_values.clear();
        m_grow_on_next_insert = false;
    }

    template<typename P>
    std::pair<iterator, bool> insert(P&& value) {
        return insert_impl(KeySelect()(value), std::forward<P>(value));
    }

    template<typename P>
    iterator insert(const_iterator hint, P&& value) {
        if(hint != cend() && compare_keys(KeySelect()(*hint), KeySelect()(value))) {
            return mutable_iterator(hint);
        }

        return insert(std::forward<P>(value)).first;
    }

    template<class InputIt>
    void insert(InputIt first, InputIt last) {
        if(std::is_base_of<std::forward_iterator_tag,
                           typename std::iterator_traits<InputIt>::iterator_category>::value)
        {
            const auto nb_elements_insert = std::distance(first, last);
            const size_type nb_free_buckets = m_load_threshold - size();
            tsl_assert(m_load_threshold >= size());

            if(nb_elements_insert > 0 && nb_free_buckets < size_type(nb_elements_insert)) {
                reserve(size() + size_type(nb_elements_insert));
            }
        }

        for(; first != last; ++first) {
            insert(*first);
        }
    }



    template<class K, class M>
    std::pair<iterator, bool> insert_or_assign(K&& key, M&& value) {
        auto it = try_emplace(std::forward<K>(key), std::forward<M>(value));
        if(!it.second) {
            it.first.value() = std::forward<M>(value);
        }

        return it;
    }

    template<class K, class M>
    iterator insert_or_assign(const_iterator hint, K&& key, M&& obj) {
        if(hint != cend() && compare_keys(KeySelect()(*hint), key)) {
            auto it = mutable_iterator(hint);
            it.value() = std::forward<M>(obj);

            return it;
        }

        return insert_or_assign(std::forward<K>(key), std::forward<M>(obj)).first;
    }



    template<class... Args>
    std::pair<iterator, bool> emplace(Args&&... args) {
        return insert(value_type(std::forward<Args>(args)...));
    }

    template<class... Args>
    iterator emplace_hint(const_iterator hint, Args&&... args) {
        return insert(hint, value_type(std::forward<Args>(args)...));
    }



    template<class K, class... Args>
    std::pair<iterator, bool> try_emplace(K&& key, Args&&... value_args) {
        return insert_impl(key, std::piecewise_construct,
                                std::forward_as_tuple(std::forward<K>(key)),
                                std::forward_as_tuple(std::forward<Args>(value_args)...));
    }

    template<class K, class... Args>
    iterator try_emplace(const_iterator hint, K&& key, Args&&... args) {
        if(hint != cend() && compare_keys(KeySelect()(*hint), key)) {
            return mutable_iterator(hint);
        }

        return try_emplace(std::forward<K>(key), std::forward<Args>(args)...).first;
    }



    /**
     * Here to avoid `template<class K> size_type erase(const K& key)` being used when
     * we use a iterator instead of a const_iterator.
     */
    iterator erase(iterator pos) {
        return erase(const_iterator(pos));
    }

    iterator erase(const_iterator pos) {
        tsl_assert(pos != cend());

        const std::size_t index_erase = iterator_to_index(pos);

        auto it_bucket = find_key(pos.key(), hash_key(pos.key()));
        tsl_assert(it_bucket != m_buckets.end());

        erase_value_from_bucket(it_bucket);

        /*
         * One element was removed from m_values, due to the left shift the next element
         * is now at the position of the previous element (or end if none).
         */
        return begin() + index_erase;
    }

    iterator erase(const_iterator first, const_iterator last) {
        if(first == last) {
            return mutable_iterator(first);
        }

        tsl_assert(std::distance(first, last) > 0);
        const std::size_t start_index = iterator_to_index(first);
        const std::size_t nb_values = std::size_t(std::distance(first, last));
        const std::size_t end_index = start_index + nb_values;

        // Delete all values
#ifdef TSL_NO_CONTAINER_ERASE_CONST_ITERATOR
        auto next_it = m_values.erase(mutable_iterator(first).m_iterator, mutable_iterator(last).m_iterator);
#else
        auto next_it = m_values.erase(first.m_iterator, last.m_iterator);
#endif

        /*
         * Mark the buckets corresponding to the values as empty and do a backward shift.
         *
         * Also, the erase operation on m_values has shifted all the values on the right of last.m_iterator.
         * Adapt the indexes for these values.
         */
        std::size_t ibucket = 0;
        while(ibucket < m_buckets.size()) {
            if(m_buckets[ibucket].empty()) {
                ibucket++;
            }
            else if(m_buckets[ibucket].index() >= start_index && m_buckets[ibucket].index() < end_index) {
                m_buckets[ibucket].clear();
                backward_shift(ibucket);
                // Don't increment ibucket, backward_shift may have replaced current bucket.
            }
            else if(m_buckets[ibucket].index() >= end_index) {
                m_buckets[ibucket].set_index(index_type(m_buckets[ibucket].index() - nb_values));
                ibucket++;
            }
            else {
                ibucket++;
            }
        }

        return iterator(next_it);
    }


    template<class K>
    size_type erase(const K& key) {
        return erase(key, hash_key(key));
    }

    template<class K>
    size_type erase(const K& key, std::size_t hash) {
        return erase_impl(key, hash);
    }

    void swap(ordered_hash& other) noexcept {
        using std::swap;

        swap(static_cast<Hash&>(*this), static_cast<Hash&>(other));
        swap(static_cast<KeyEqual&>(*this), static_cast<KeyEqual&>(other));
        swap(m_buckets, other.m_buckets);
        swap(m_mask, other.m_mask);
        swap(m_values, other.m_values);
        swap(m_grow_on_next_insert, other.m_grow_on_next_insert);
        swap(m_max_load_factor, other.m_max_load_factor);
        swap(m_load_threshold, other.m_load_threshold);
    }




    /*
     * Lookup
     */
    template<class K, class U = ValueSelect, typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
    typename U::value_type& at(const K& key) {
        return at(key, hash_key(key));
    }

    template<class K, class U = ValueSelect, typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
    typename U::value_type& at(const K& key, std::size_t hash) {
        return const_cast<typename U::value_type&>(static_cast<const ordered_hash*>(this)->at(key, hash));
    }

    template<class K, class U = ValueSelect, typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
    const typename U::value_type& at(const K& key) const {
        return at(key, hash_key(key));
    }

    template<class K, class U = ValueSelect, typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
    const typename U::value_type& at(const K& key, std::size_t hash) const {
        auto it = find(key, hash);
        if(it != end()) {
            return it.value();
        }
        else {
            throw std::out_of_range("Couldn't find the key.");
        }
    }


    template<class K, class U = ValueSelect, typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
    typename U::value_type& operator[](K&& key) {
        return try_emplace(std::forward<K>(key)).first.value();
    }


    template<class K>
    size_type count(const K& key) const {
        return count(key, hash_key(key));
    }

    template<class K>
    size_type count(const K& key, std::size_t hash) const {
        if(find(key, hash) == cend()) {
            return 0;
        }
        else {
            return 1;
        }
    }

    template<class K>
    iterator find(const K& key) {
        return find(key, hash_key(key));
    }

    template<class K>
    iterator find(const K& key, std::size_t hash) {
        auto it_bucket = find_key(key, hash);
        return (it_bucket != m_buckets.end())?iterator(m_values.begin() + it_bucket->index()):end();
    }

    template<class K>
    const_iterator find(const K& key) const {
        return find(key, hash_key(key));
    }

    template<class K>
    const_iterator find(const K& key, std::size_t hash) const {
        auto it_bucket = find_key(key, hash);
        return (it_bucket != m_buckets.cend())?const_iterator(m_values.begin() + it_bucket->index()):end();
    }


    template<class K>
    std::pair<iterator, iterator> equal_range(const K& key) {
        return equal_range(key, hash_key(key));
    }

    template<class K>
    std::pair<iterator, iterator> equal_range(const K& key, std::size_t hash) {
        iterator it = find(key, hash);
        return std::make_pair(it, (it == end())?it:std::next(it));
    }

    template<class K>
    std::pair<const_iterator, const_iterator> equal_range(const K& key) const {
        return equal_range(key, hash_key(key));
    }

    template<class K>
    std::pair<const_iterator, const_iterator> equal_range(const K& key, std::size_t hash) const {
        const_iterator it = find(key, hash);
        return std::make_pair(it, (it == cend())?it:std::next(it));
    }


    /*
     * Bucket interface
     */
    size_type bucket_count() const {
        return m_buckets.size();
    }

    size_type max_bucket_count() const {
        return m_buckets.max_size();
    }

    /*
     *  Hash policy
     */
    float load_factor() const {
        return float(size())/float(bucket_count());
    }

    float max_load_factor() const {
        return m_max_load_factor;
    }

    void max_load_factor(float ml) {
        m_max_load_factor = std::max(0.1f, std::min(ml, 0.95f));
        m_load_threshold = size_type(float(bucket_count())*m_max_load_factor);
    }

    void rehash(size_type count) {
        count = std::max(count, size_type(std::ceil(float(size())/max_load_factor())));
        rehash_impl(count);
    }

    void reserve(size_type count) {
        reserve_space_for_values(count);

        count = size_type(std::ceil(float(count)/max_load_factor()));
        rehash(count);
    }


    /*
     * Observers
     */
    hasher hash_function() const {
        return static_cast<const Hash&>(*this);
    }

    key_equal key_eq() const {
        return static_cast<const KeyEqual&>(*this);
    }


    /*
     * Other
     */
    iterator mutable_iterator(const_iterator pos) {
        return iterator(m_values.begin() + iterator_to_index(pos));
    }

    iterator nth(size_type index) {
        return iterator(m_values.begin() + index);
    }

    const_iterator nth(size_type index) const {
        return const_iterator(m_values.cbegin() + index);
    }

    const_reference front() const {
        return m_values.front();
    }

    const_reference back() const {
        return m_values.back();
    }

    const values_container_type& values_container() const noexcept {
        return m_values;
    }

    template<class U = values_container_type, typename std::enable_if<is_vector<U>::value>::type* = nullptr>
    const typename values_container_type::value_type* data() const noexcept {
        return m_values.data();
    }

    template<class U = values_container_type, typename std::enable_if<is_vector<U>::value>::type* = nullptr>
    size_type capacity() const noexcept {
        return m_values.capacity();
    }

    void shrink_to_fit() {
        m_values.shrink_to_fit();
    }


    template<typename P>
    std::pair<iterator, bool> insert_at_position(const_iterator pos, P&& value) {
        return insert_at_position_impl(pos.m_iterator, KeySelect()(value), std::forward<P>(value));
    }

    template<class... Args>
    std::pair<iterator, bool> emplace_at_position(const_iterator pos, Args&&... args) {
        return insert_at_position(pos, value_type(std::forward<Args>(args)...));
    }

    template<class K, class... Args>
    std::pair<iterator, bool> try_emplace_at_position(const_iterator pos, K&& key, Args&&... value_args) {
        return insert_at_position_impl(pos.m_iterator, key,
                                       std::piecewise_construct,
                                       std::forward_as_tuple(std::forward<K>(key)),
                                       std::forward_as_tuple(std::forward<Args>(value_args)...));
    }


    void pop_back() {
        tsl_assert(!empty());
        erase(std::prev(end()));
    }


    /**
     * Here to avoid `template<class K> size_type unordered_erase(const K& key)` being used when
     * we use a iterator instead of a const_iterator.
     */
    iterator unordered_erase(iterator pos) {
        return unordered_erase(const_iterator(pos));
    }

    iterator unordered_erase(const_iterator pos) {
        const std::size_t index_erase = iterator_to_index(pos);
        unordered_erase(pos.key());

        /*
         * One element was deleted, index_erase now points to the next element as the elements after
         * the deleted value were shifted to the left in m_values (will be end() if we deleted the last element).
         */
        return begin() + index_erase;
    }

    template<class K>
    size_type unordered_erase(const K& key) {
        return unordered_erase(key, hash_key(key));
    }

    template<class K>
    size_type unordered_erase(const K& key, std::size_t hash) {
        auto it_bucket_key = find_key(key, hash);
        if(it_bucket_key == m_buckets.end()) {
            return 0;
        }

        /**
         * If we are not erasing the last element in m_values, we swap
         * the element we are erasing with the last element. We then would
         * just have to do a pop_back() in m_values.
         */
        if(!compare_keys(key, KeySelect()(back()))) {
            auto it_bucket_last_elem = find_key(KeySelect()(back()), hash_key(KeySelect()(back())));
            tsl_assert(it_bucket_last_elem != m_buckets.end());
            tsl_assert(it_bucket_last_elem->index() == m_values.size() - 1);

            using std::swap;
            swap(m_values[it_bucket_key->index()], m_values[it_bucket_last_elem->index()]);
            swap(it_bucket_key->index_ref(), it_bucket_last_elem->index_ref());
        }

        erase_value_from_bucket(it_bucket_key);

        return 1;
    }

    friend bool operator==(const ordered_hash& lhs, const ordered_hash& rhs) {
        return lhs.m_values == rhs.m_values;
    }

    friend bool operator!=(const ordered_hash& lhs, const ordered_hash& rhs) {
        return lhs.m_values != rhs.m_values;
    }

    friend bool operator<(const ordered_hash& lhs, const ordered_hash& rhs) {
        return lhs.m_values < rhs.m_values;
    }

    friend bool operator<=(const ordered_hash& lhs, const ordered_hash& rhs) {
        return lhs.m_values <= rhs.m_values;
    }

    friend bool operator>(const ordered_hash& lhs, const ordered_hash& rhs) {
        return lhs.m_values > rhs.m_values;
    }

    friend bool operator>=(const ordered_hash& lhs, const ordered_hash& rhs) {
        return lhs.m_values >= rhs.m_values;
    }


private:
    template<class K>
    std::size_t hash_key(const K& key) const {
        return Hash::operator()(key);
    }

    template<class K1, class K2>
    bool compare_keys(const K1& key1, const K2& key2) const {
        return KeyEqual::operator()(key1, key2);
    }

    template<class K>
    typename buckets_container_type::iterator find_key(const K& key, std::size_t hash) {
        auto it = static_cast<const ordered_hash*>(this)->find_key(key, hash);
        return m_buckets.begin() + std::distance(m_buckets.cbegin(), it);
    }

    /**
     * Return bucket which has the key 'key' or m_buckets.end() if none.
     *
     * From the bucket_for_hash, search for the value until we either find an empty bucket
     * or a bucket which has a value with a distance from its ideal bucket longer
     * than the probe length for the value we are looking for.
     */
    template<class K>
    typename buckets_container_type::const_iterator find_key(const K& key, std::size_t hash) const {
        for(std::size_t ibucket = bucket_for_hash(hash), dist_from_ideal_bucket = 0; ;
            ibucket = next_bucket(ibucket), dist_from_ideal_bucket++)
        {
            if(m_buckets[ibucket].empty()) {
                return m_buckets.end();
            }
            else if(m_buckets[ibucket].truncated_hash() == bucket_entry::truncate_hash(hash) &&
                    compare_keys(key, KeySelect()(m_values[m_buckets[ibucket].index()])))
            {
                return m_buckets.begin() + ibucket;
            }
            else if(dist_from_ideal_bucket > distance_from_ideal_bucket(ibucket)) {
                return m_buckets.end();
            }
        }
    }

    void rehash_impl(size_type bucket_count) {
        bucket_count = round_up_to_power_of_two(bucket_count);
        tsl_assert(bucket_count > 0);

        if(bucket_count == this->bucket_count()) {
            return;
        }

        if(bucket_count > max_bucket_count()) {
            throw std::length_error("The map exceeds its maxmimum size.");
        }


        buckets_container_type old_buckets(bucket_count);
        m_buckets.swap(old_buckets);
        // Everything should be noexcept from here.

        m_mask = bucket_count - 1;
        this->max_load_factor(m_max_load_factor);
        m_grow_on_next_insert = false;



        for(const bucket_entry& old_bucket: old_buckets) {
            if(old_bucket.empty()) {
                continue;
            }

            truncated_hash_type insert_hash = old_bucket.truncated_hash();
            index_type insert_index = old_bucket.index();

            for(std::size_t ibucket = bucket_for_hash(insert_hash), dist_from_ideal_bucket = 0; ;
                ibucket = next_bucket(ibucket), dist_from_ideal_bucket++)
            {
                if(m_buckets[ibucket].empty()) {
                    m_buckets[ibucket].set_index(insert_index);
                    m_buckets[ibucket].set_hash(insert_hash);
                    break;
                }

                const std::size_t distance = distance_from_ideal_bucket(ibucket);
                if(dist_from_ideal_bucket > distance) {
                    std::swap(insert_index, m_buckets[ibucket].index_ref());
                    std::swap(insert_hash, m_buckets[ibucket].truncated_hash_ref());
                    dist_from_ideal_bucket = distance;
                }
            }
        }
    }

    template<class T = values_container_type, typename std::enable_if<is_vector<T>::value>::type* = nullptr>
    void reserve_space_for_values(size_type count) {
        m_values.reserve(count);
    }

    template<class T = values_container_type, typename std::enable_if<!is_vector<T>::value>::type* = nullptr>
    void reserve_space_for_values(size_type /*count*/) {
    }

    /**
     * Swap the empty bucket with the values on its right until we cross another empty bucket
     * or if the other bucket has a distance_from_ideal_bucket == 0.
     */
    void backward_shift(std::size_t empty_ibucket) noexcept {
        tsl_assert(m_buckets[empty_ibucket].empty());

        std::size_t previous_ibucket = empty_ibucket;
        for(std::size_t current_ibucket = next_bucket(previous_ibucket);
            !m_buckets[current_ibucket].empty() && distance_from_ideal_bucket(current_ibucket) > 0;
            previous_ibucket = current_ibucket, current_ibucket = next_bucket(current_ibucket))
        {
            std::swap(m_buckets[current_ibucket], m_buckets[previous_ibucket]);
        }
    }

    void erase_value_from_bucket(typename buckets_container_type::iterator it_bucket) {
        tsl_assert(it_bucket != m_buckets.end() && !it_bucket->empty());

        m_values.erase(m_values.begin() + it_bucket->index());

        /*
         * m_values.erase shifted all the values on the right of the erased value,
         * shift the indexes by 1 in the buckets array for these values.
         */
        if(it_bucket->index() != m_values.size()) {
            shift_indexes_in_buckets(it_bucket->index(), short(1));
        }

        // Mark the bucket as empty and do a backward shift of the values on the right
        it_bucket->clear();
        backward_shift(std::size_t(std::distance(m_buckets.begin(), it_bucket)));
    }

    /**
     * Go through each value from [from_ivalue, m_values.size()) in m_values and for each
     * bucket corresponding to the value, shift the indexes to the left by delta.
     */
    void shift_indexes_in_buckets(index_type from_ivalue, short delta) noexcept  {
        static_assert(std::is_unsigned<index_type>::value && sizeof(index_type) >= sizeof(short),
                      "index_type should be unsigned and sizeof(index_type) >= sizeof(short)");

        for(std::size_t ivalue = from_ivalue; ivalue < m_values.size(); ivalue++) {
            std::size_t ibucket = bucket_for_hash(hash_key(KeySelect()(m_values[ivalue])));

            // Modulo arithmetic, we should be alright for index_type(ivalue + delta). TODO further checks
            while(m_buckets[ibucket].index() != index_type(ivalue + delta)) {
                ibucket = next_bucket(ibucket);
            }

            m_buckets[ibucket].set_index(index_type(m_buckets[ibucket].index() - delta));
        }
    }

    template<class K>
    size_type erase_impl(const K& key, std::size_t hash) {
        auto it_bucket = find_key(key, hash);
        if(it_bucket != m_buckets.end()) {
            erase_value_from_bucket(it_bucket);

            return 1;
        }
        else {
            return 0;
        }
    }

    template<class K, class... Args>
    std::pair<iterator, bool> insert_impl(const K& key, Args&&... value_type_args) {
        return insert_at_position_impl(m_values.cend(), key, std::forward<Args>(value_type_args)...);
    }

    /**
     * Insert the element before insert_position.
     */
    template<class K, class... Args>
    std::pair<iterator, bool> insert_at_position_impl(typename values_container_type::const_iterator insert_position,
                                                      const K& key, Args&&... value_type_args)
    {
        const std::size_t hash = hash_key(key);

        std::size_t ibucket = bucket_for_hash(hash);
        std::size_t dist_from_ideal_bucket = 0;

        while(!m_buckets[ibucket].empty() && dist_from_ideal_bucket <= distance_from_ideal_bucket(ibucket)) {
            if(m_buckets[ibucket].truncated_hash() == bucket_entry::truncate_hash(hash) &&
               compare_keys(key, KeySelect()(m_values[m_buckets[ibucket].index()])))
            {
                return std::make_pair(begin() + m_buckets[ibucket].index(), false);
            }

            ibucket = next_bucket(ibucket);
            dist_from_ideal_bucket++;
        }

        if(size() >= max_size()) {
            throw std::length_error("We reached the maximum size for the hash table.");
        }


        if(grow_on_high_load()) {
            ibucket = bucket_for_hash(hash);
            dist_from_ideal_bucket = 0;
        }


        const index_type index_insert_position = index_type(std::distance(m_values.cbegin(), insert_position));

#ifdef TSL_NO_CONTAINER_EMPLACE_CONST_ITERATOR
        m_values.emplace(m_values.begin() + std::distance(m_values.cbegin(), insert_position), std::forward<Args>(value_type_args)...);
#else
        m_values.emplace(insert_position, std::forward<Args>(value_type_args)...);
#endif

        insert_index(ibucket, dist_from_ideal_bucket,
                     index_insert_position, bucket_entry::truncate_hash(hash));

        /*
         * The insertion didn't happend at the end of the m_values container,
         * we need to shift the indexes in m_buckets.
         */
        if(index_insert_position != m_values.size() - 1) {
            shift_indexes_in_buckets(index_insert_position + 1, short(-1));
        }

        return std::make_pair(iterator(m_values.begin() + index_insert_position), true);
    }

    void insert_index(std::size_t ibucket, std::size_t dist_from_ideal_bucket,
                      index_type index_insert, truncated_hash_type hash_insert) noexcept
    {
        while(!m_buckets[ibucket].empty()) {
            const std::size_t distance = distance_from_ideal_bucket(ibucket);
            if(dist_from_ideal_bucket > distance) {
                std::swap(index_insert, m_buckets[ibucket].index_ref());
                std::swap(hash_insert, m_buckets[ibucket].truncated_hash_ref());

                dist_from_ideal_bucket = distance;
            }


            ibucket = next_bucket(ibucket);
            dist_from_ideal_bucket++;


            if(dist_from_ideal_bucket > REHASH_ON_HIGH_NB_PROBES__NPROBES && !m_grow_on_next_insert &&
               load_factor() >= REHASH_ON_HIGH_NB_PROBES__MIN_LOAD_FACTOR)
            {
                // We don't want to grow the map now as we need this method to be noexcept.
                // Do it on next insert.
                m_grow_on_next_insert = true;
            }
        }


        m_buckets[ibucket].set_index(index_insert);
        m_buckets[ibucket].set_hash(hash_insert);
    }

    std::size_t distance_from_ideal_bucket(std::size_t ibucket) const noexcept {
        const std::size_t ideal_bucket = bucket_for_hash(m_buckets[ibucket].truncated_hash());

        if(ibucket >= ideal_bucket) {
            return ibucket - ideal_bucket;
        }
        // If the bucket is smaller than the ideal bucket for the value, there was a wrapping at the end of the
        // bucket array due to the modulo.
        else {
            return (bucket_count() + ibucket) - ideal_bucket;
        }
    }

    std::size_t next_bucket(std::size_t index) const noexcept {
        tsl_assert(index < m_buckets.size());

        index++;
        return (index < m_buckets.size())?index:0;
    }

    std::size_t bucket_for_hash(std::size_t hash) const noexcept {
        return hash & m_mask;
    }

    std::size_t iterator_to_index(const_iterator it) const noexcept {
        const auto dist = std::distance(cbegin(), it);
        tsl_assert(dist >= 0);

        return std::size_t(dist);
    }

    /**
     * Return true if the map has been rehashed.
     */
    bool grow_on_high_load() {
        if(m_grow_on_next_insert || size() >= m_load_threshold) {
            rehash_impl(bucket_count() * 2);
            m_grow_on_next_insert = false;

            return true;
        }
        else {
            return false;
        }
    }

    static std::size_t round_up_to_power_of_two(std::size_t value) {
        if(is_power_of_two(value)) {
            return value;
        }

        if(value == 0) {
            return 1;
        }

        --value;
        for(std::size_t i = 1; i < sizeof(std::size_t) * CHAR_BIT; i *= 2) {
            value |= value >> i;
        }

        return value + 1;
    }

    static constexpr bool is_power_of_two(std::size_t value) {
        return value != 0 && (value & (value - 1)) == 0;
    }


public:
    static const size_type DEFAULT_INIT_BUCKETS_SIZE = 16;
    static constexpr float DEFAULT_MAX_LOAD_FACTOR = 0.75f;

private:
    static const size_type REHASH_ON_HIGH_NB_PROBES__NPROBES = 128;
    static constexpr float REHASH_ON_HIGH_NB_PROBES__MIN_LOAD_FACTOR = 0.15f;

private:
    buckets_container_type m_buckets;
    size_type m_mask;

    values_container_type m_values;

    bool m_grow_on_next_insert;
    float m_max_load_factor;
    size_type m_load_threshold;
};


} // end namespace detail_ordered_hash

} // end namespace tsl

#endif