hash_table7.hpp

// emhash7::HashMap for C++11/14/17
// version 2.2.5
// https://github.com/ktprime/emhash/blob/master/hash_table7.hpp
//
// Licensed under the MIT License <https://opensource.org/licenses/MIT>.
// SPDX-License-Identifier: MIT
// Copyright (c) 2019-2024 Huang Yuanbing & bailuzhou AT 163.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

// From
// NUMBER OF PROBES / LOOKUP       Successful            Unsuccessful
// Quadratic collision resolution  1 - ln(1-L) - L/2     1/(1-L) - L - ln(1-L)
// Linear collision resolution     [1+1/(1-L)]/2         [1+1/(1-L)2]/2
// separator chain resolution      1 + L / 2             exp(-L) + L

// -- enlarge_factor --           0.10  0.50  0.60  0.75  0.80  0.90  0.99
// QUADRATIC COLLISION RES.
//    probes/successful lookup    1.05  1.44  1.62  2.01  2.21  2.85  5.11
//    probes/unsuccessful lookup  1.11  2.19  2.82  4.64  5.81  11.4  103.6
// LINEAR COLLISION RES.
//    probes/successful lookup    1.06  1.5   1.75  2.5   3.0   5.5   50.5
//    probes/unsuccessful lookup  1.12  2.5   3.6   8.5   13.0  50.0
// SEPARATE CHAN RES.
//    probes/successful lookup    1.05  1.25  1.3   1.25  1.4   1.45  1.50
//    probes/unsuccessful lookup  1.00  1.11  1.15  1.22  1.25  1.31  1.37
//    clacul/unsuccessful lookup  1.01  1.25  1.36, 1.56, 1.64, 1.81, 1.97

/****************
    under random hashCodes, the frequency of nodes in bins follows a Poisson
distribution(https://en.wikipedia.org/wiki/Poisson_distribution) with a parameter of about 0.5
on average for the default resizing threshold of 0.75, although with a large variance because
of resizing granularity. Ignoring variance, the expected occurrences of list size k are
(exp(-0.5) * pow(0.5, k)/factorial(k)). The first values are:
0: 0.60653066
1: 0.30326533
2: 0.07581633
3: 0.01263606
4: 0.00157952
5: 0.00015795
6: 0.00001316
7: 0.00000094
8: 0.00000006

  ============== buckets size ration ========
    1   1543981  0.36884964|0.36787944  36.885
    2    768655  0.36725597|0.36787944  73.611
    3    256236  0.18364065|0.18393972  91.975
    4     64126  0.06127757|0.06131324  98.102
    5     12907  0.01541710|0.01532831  99.644
    6      2050  0.00293841|0.00306566  99.938
    7       310  0.00051840|0.00051094  99.990
    8        49  0.00009365|0.00007299  99.999
    9         4  0.00000860|0.00000913  100.000
========== collision miss ration ===========
  _num_filled aver_size k.v size_kv = 4185936, 1.58, x.x 24
  collision,possion,cache_miss hit_find|hit_miss, load_factor = 36.73%,36.74%,31.31%  1.50|2.00, 1.00
============== buckets size ration ========
*******************************************************/

#pragma once

#include <cstring>
#include <string>
#include <cmath>
#include <cstdlib>
#include <type_traits>
#include <cassert>
#include <utility>
#include <cstdint>
#include <functional>
#include <iterator>
#include <algorithm>

#if EMH_WY_HASH
    #include "wyhash.h"
#endif

#ifdef EMH_NEW
    #undef  EMH_KEY
    #undef  EMH_VAL
    #undef  EMH_PKV
    #undef  EMH_NEW
    #undef  EMH_SET
    #undef  EMH_BUCKET
    #undef  EMH_EMPTY
#endif

// likely/unlikely
#if (__GNUC__ >= 4 || __clang__)
#    define EMH_LIKELY(condition)   __builtin_expect(condition, 1)
#    define EMH_UNLIKELY(condition) __builtin_expect(condition, 0)
#else
#    define EMH_LIKELY(condition)   condition
#    define EMH_UNLIKELY(condition) condition
#endif

#ifndef EMH_BUCKET_INDEX
    #define EMH_BUCKET_INDEX 1
#endif

#if EMH_BUCKET_INDEX == 0
    #define EMH_KEY(p,n)     p[n].second.first
    #define EMH_VAL(p,n)     p[n].second.second
    #define EMH_BUCKET(p,n)  p[n].first
    #define EMH_PKV(p,n)     p[n].second
    #define EMH_NEW(key, val, bucket)\
            new(_pairs + bucket) PairT(bucket, value_type(key, val));\
            _num_filled ++;  EMH_SET(bucket)
#elif EMH_BUCKET_INDEX == 2
    #define EMH_KEY(p,n)     p[n].first.first
    #define EMH_VAL(p,n)     p[n].first.second
    #define EMH_BUCKET(p,n)  p[n].second
    #define EMH_PKV(p,n)     p[n].first
    #define EMH_NEW(key, val, bucket)\
            new(_pairs + bucket) PairT(value_type(key, val), bucket);\
            _num_filled ++;  EMH_SET(bucket)
#else
    #define EMH_KEY(p,n)     p[n].first
    #define EMH_VAL(p,n)     p[n].second
    #define EMH_BUCKET(p,n)  p[n].bucket
    #define EMH_PKV(p,n)     p[n]
    #define EMH_NEW(key, val, bucket)\
            new(_pairs + bucket) PairT(key, val, bucket);\
            _num_filled ++; EMH_SET(bucket)
#endif

#define EMH_MASK(n)       1 << (n % MASK_BIT)
#define EMH_SET(n)        _bitmask[n / MASK_BIT] &= ~(EMH_MASK(n))
#define EMH_CLS(n)        _bitmask[n / MASK_BIT] |= EMH_MASK(n)
#define EMH_EMPTY(n)      (_bitmask[n / MASK_BIT] & (EMH_MASK(n))) != 0

#if _WIN32
    #include <intrin.h>
#if _WIN64
    #pragma intrinsic(_umul128)
#endif
#endif

namespace emhash7 {

#ifdef EMH_SIZE_TYPE_16BIT
    typedef uint16_t size_type;
    static constexpr size_type INACTIVE = 0xFFFF;
#elif EMH_SIZE_TYPE_64BIT
    typedef uint64_t size_type;
    static constexpr size_type INACTIVE = 0 - 0x1ull;
#else
    typedef uint32_t size_type;
    static constexpr size_type INACTIVE = 0 - 0x1u;
#endif

#ifndef EMH_MALIGN
    static constexpr uint32_t EMH_MALIGN = 16;
#endif
static_assert(EMH_MALIGN >= 16 && 0 == (EMH_MALIGN & (EMH_MALIGN - 1)));

#ifndef EMH_SIZE_TYPE_16BIT
static_assert((int)INACTIVE < 0, "INACTIVE must negative (to int)");
#endif

//count the leading zero bit
static inline int CTZ(size_t n)
{
#if defined(__x86_64__) || defined(_WIN32) || (__BYTE_ORDER__ && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)

#elif __BIG_ENDIAN__ || (__BYTE_ORDER__ && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
    n = __builtin_bswap64(n);
#else
    static uint32_t endianness = 0x12345678;
    const auto is_big = *(const char *)&endianness == 0x12;
    if (is_big)
    n = __builtin_bswap64(n);
#endif

#if _WIN32
    unsigned long index;
    #if defined(_WIN64)
    _BitScanForward64(&index, n);
    #else
    _BitScanForward(&index, n);
    #endif
#elif defined (__LP64__) || (SIZE_MAX == UINT64_MAX) || defined (__x86_64__)
    auto index = __builtin_ctzll(n);
#elif 1
    auto index = __builtin_ctzl(n);
#else
    #if defined (__LP64__) || (SIZE_MAX == UINT64_MAX) || defined (__x86_64__)
    size_type index;
    __asm__("bsfq %1, %0\n" : "=r" (index) : "rm" (n) : "cc");
    #else
    size_type index;
    __asm__("bsf %1, %0\n" : "=r" (index) : "rm" (n) : "cc");
    #endif
#endif

    return (int)index;
}

template <typename First, typename Second>
struct entry {
    using first_type =  First;
    using second_type = Second;
    entry(const First& key, const Second& val, size_type ibucket)
        :second(val), first(key)
    {
        bucket = ibucket;
    }

    entry(First&& key, Second&& val, size_type ibucket)
        :second(std::move(val)), first(std::move(key))
    {
        bucket = ibucket;
    }

    template<typename K, typename V>
    entry(K&& key, V&& val, size_type ibucket)
        :second(std::forward<V>(val)), first(std::forward<K>(key))
    {
        bucket = ibucket;
    }

    entry(const std::pair<First, Second>& pair)
        :second(pair.second), first(pair.first)
    {
        bucket = INACTIVE;
    }

    entry(std::pair<First, Second>&& pair)
        :second(std::move(pair.second)), first(std::move(pair.first))
    {
        bucket = INACTIVE;
    }

    entry(std::tuple<First, Second>&& tup)
        :second(std::move(std::get<2>(tup))), first(std::move(std::get<1>(tup)))
    {
        bucket = INACTIVE;
    }

    entry(const entry& rhs)
        :second(rhs.second), first(rhs.first)
    {
        bucket = rhs.bucket;
    }

    entry(entry&& rhs) noexcept
        :second(std::move(rhs.second)), first(std::move(rhs.first))
    {
        bucket = rhs.bucket;
    }

    entry& operator = (entry&& rhs) noexcept
    {
        second = std::move(rhs.second);
        bucket = rhs.bucket;
        first  = std::move(rhs.first);
        return *this;
    }

    entry& operator = (const entry& rhs)
    {
        second = rhs.second;
        bucket = rhs.bucket;
        first  = rhs.first;
        return *this;
    }

    bool operator == (const entry<First, Second>& p) const
    {
        return first == p.first && second == p.second;
    }

    bool operator == (const std::pair<First, Second>& p) const
    {
        return first == p.first && second == p.second;
    }

    void swap(entry<First, Second>& o)
    {
        std::swap(second, o.second);
        std::swap(first, o.first);
    }

#if EMH_ORDER_KV || EMH_SIZE_TYPE_64BIT
    First first;
    size_type bucket;
    Second second;
#else
    Second second;
    size_type bucket;
    First first;
#endif
};

/// A cache-friendly hash table with open addressing, linear/qua probing and power-of-two capacity
template <typename KeyT, typename ValueT, typename HashT = std::hash<KeyT>, typename EqT = std::equal_to<KeyT>>
class HashMap
{
#ifndef EMH_DEFAULT_LOAD_FACTOR
    constexpr static float EMH_DEFAULT_LOAD_FACTOR = 0.80f;
    constexpr static float EMH_MIN_LOAD_FACTOR     = 0.25f; //< 0.5
#endif

public:
    typedef HashMap<KeyT, ValueT, HashT, EqT> htype;
    typedef std::pair<KeyT, ValueT>           value_type;

#if EMH_BUCKET_INDEX == 0
    typedef value_type                        value_pair;
    typedef std::pair<size_type, value_type>  PairT;
#elif EMH_BUCKET_INDEX == 2
    typedef value_type                        value_pair;
    typedef std::pair<value_type, size_type>  PairT;
#else
    typedef entry<KeyT, ValueT>               value_pair;
    typedef entry<KeyT, ValueT>               PairT;
#endif

    typedef KeyT   key_type;
    typedef ValueT val_type;
    typedef ValueT mapped_type;
    typedef HashT  hasher;
    typedef EqT    key_equal;
    typedef PairT&       reference;
    typedef const PairT& const_reference;

    class const_iterator;
    class iterator
    {
    public:
        typedef std::forward_iterator_tag iterator_category;
        typedef std::ptrdiff_t            difference_type;
        typedef value_pair                value_type;

        typedef value_pair*               pointer;
        typedef value_pair&               reference;

        iterator() = default;
        iterator(const const_iterator& it) : _map(it._map), _bucket(it._bucket), _from(it._from), _bmask(it._bmask) { }
        //iterator(const htype* hash_map, size_type bucket, bool) : _map(hash_map), _bucket(bucket) { init(); }
#if EMH_ITER_SAFE
        iterator(const htype* hash_map, size_type bucket) : _map(hash_map), _bucket(bucket) { init(); }
#else
        iterator(const htype* hash_map, size_type bucket) : _map(hash_map), _bucket(bucket) { _from = -1; }
#endif

        void init()
        {
            _from = (_bucket / SIZE_BIT) * SIZE_BIT;
            if (_bucket < _map->bucket_count()) {
                _bmask = *(size_t*)((size_t*)_map->_bitmask + _from / SIZE_BIT);
                _bmask |= (1ull << _bucket % SIZE_BIT) - 1;
                _bmask = ~_bmask;
            } else {
                _bmask = 0;
            }
        }

        size_type bucket() const
        {
            return _bucket;
        }

        void clear(size_type bucket)
        {
            if (_bucket / SIZE_BIT == bucket / SIZE_BIT)
                _bmask &= ~(1ull << (bucket % SIZE_BIT));
        }

        iterator& next()
        {
            goto_next_element();
            return *this;
        }

        iterator& operator++()
        {
#ifndef EMH_ITER_SAFE
            if (_from == (size_type)-1) init();
#endif
            _bmask &= _bmask - 1;
            goto_next_element();
            return *this;
        }

        iterator operator++(int)
        {
#ifndef EMH_ITER_SAFE
            if (_from == (size_type)-1) init();
#endif
            iterator old = *this;
            _bmask &= _bmask - 1;
            goto_next_element();
            return old;
        }

        reference operator*() const
        {
            return _map->EMH_PKV(_pairs, _bucket);
        }

        pointer operator->() const
        {
            return &(_map->EMH_PKV(_pairs, _bucket));
        }

        bool operator==(const iterator& rhs) const { return _bucket == rhs._bucket; }
        bool operator!=(const iterator& rhs) const { return _bucket != rhs._bucket; }
        bool operator==(const const_iterator& rhs) const { return _bucket == rhs._bucket; }
        bool operator!=(const const_iterator& rhs) const { return _bucket != rhs._bucket; }

    private:
        void goto_next_element()
        {
            if (_bmask != 0) {
                _bucket = _from + CTZ(_bmask);
                return;
            }

            do {
                _bmask = ~*(size_t*)((size_t*)_map->_bitmask + (_from += SIZE_BIT) / SIZE_BIT);
            } while (_bmask == 0);

            _bucket = _from + CTZ(_bmask);
        }

    public:
        const htype* _map;
        size_type _bucket;
        size_type _from;
        size_t    _bmask;
    };

    class const_iterator
    {
    public:
        typedef std::forward_iterator_tag iterator_category;
        typedef std::ptrdiff_t            difference_type;
        typedef value_pair                value_type;

        typedef const value_pair*          pointer;
        typedef const value_pair&          reference;

        const_iterator(const iterator& it) : _map(it._map), _bucket(it._bucket), _from(it._from), _bmask(it._bmask) { }
        //const_iterator(const htype* hash_map, size_type bucket, bool) : _map(hash_map), _bucket(bucket) { init(); }
#if EMH_ITER_SAFE
        const_iterator(const htype* hash_map, size_type bucket) : _map(hash_map), _bucket(bucket) { init(); }
#else
        const_iterator(const htype* hash_map, size_type bucket) : _map(hash_map), _bucket(bucket) { _from = -1; }
#endif

        void init()
        {
            _from = (_bucket / SIZE_BIT) * SIZE_BIT;
            if (_bucket < _map->bucket_count()) {
                _bmask = *(size_t*)((size_t*)_map->_bitmask + _from / SIZE_BIT);
                _bmask |= (1ull << _bucket % SIZE_BIT) - 1;
                _bmask = ~_bmask;
            } else {
                _bmask = 0;
            }
        }

        size_type bucket() const
        {
            return _bucket;
        }

        const_iterator& operator++()
        {
#ifndef EMH_ITER_SAFE
            if (_from == (size_type)-1) init();
#endif
            goto_next_element();
            return *this;
        }

        const_iterator operator++(int)
        {
#ifndef EMH_ITER_SAFE
            if (_from == (size_type)-1) init();
#endif
            const_iterator old(*this);
            goto_next_element();
            return old;
        }

        reference operator*() const
        {
            return _map->EMH_PKV(_pairs, _bucket);
        }

        pointer operator->() const
        {
            return &(_map->EMH_PKV(_pairs, _bucket));
        }

        bool operator==(const const_iterator& rhs) const { return _bucket == rhs._bucket; }
        bool operator!=(const const_iterator& rhs) const { return _bucket != rhs._bucket; }

    private:
        void goto_next_element()
        {
            _bmask &= _bmask - 1;
            if (_bmask != 0) {
                _bucket = _from + CTZ(_bmask);
                return;
            }

            do {
                _bmask = ~*(size_t*)((size_t*)_map->_bitmask + (_from += SIZE_BIT) / SIZE_BIT);
            } while (_bmask == 0);

            _bucket = _from + CTZ(_bmask);
        }

    public:
        const htype* _map;
        size_type _bucket;
        size_type _from;
        size_t    _bmask;
    };

    void init(size_type bucket, float mlf = EMH_DEFAULT_LOAD_FACTOR)
    {
        _pairs = nullptr;
        _bitmask = nullptr;
        _num_buckets = _num_filled = 0;
        _mlf = (uint32_t)((1 << 27) / EMH_DEFAULT_LOAD_FACTOR);
        max_load_factor(mlf);
        rehash(bucket);
    }

    HashMap(size_type bucket = 2, float mlf = EMH_DEFAULT_LOAD_FACTOR) noexcept
    {
        init(bucket, mlf);
    }

    static size_t AllocSize(uint64_t num_buckets)
    {
        return (num_buckets + EPACK_SIZE) * sizeof(PairT) + (num_buckets + 7) / 8 + BIT_PACK;
    }

    static PairT* alloc_bucket(size_type num_buckets)
    {
#ifdef EMH_ALLOC
        auto* new_pairs = (PairT*)aligned_alloc(EMH_MALIGN, AllocSize(num_buckets));
#else
        auto* new_pairs = (PairT*)malloc(AllocSize(num_buckets));
#endif
        return new_pairs;
    }

    HashMap(const HashMap& rhs) noexcept
    {
        if (rhs.load_factor() > EMH_MIN_LOAD_FACTOR) {
            _pairs = (PairT*)alloc_bucket(rhs._num_buckets);
            clone(rhs);
        } else {
            init(rhs._num_filled + 2, EMH_DEFAULT_LOAD_FACTOR);
            for (auto it = rhs.begin(); it != rhs.end(); ++it)
                insert_unique(it->first, it->second);
        }
    }

    HashMap(HashMap&& rhs) noexcept
    {
#ifndef EMH_ZERO_MOVE
        init(4);
#else
        _num_buckets = _num_filled = _mask = 0;
        _pairs = nullptr;
#endif
        swap(rhs);
    }

    HashMap(std::initializer_list<value_type> ilist)
    {
        init((size_type)ilist.size());
        for (auto it = ilist.begin(); it != ilist.end(); ++it)
            do_insert(*it);
    }

    template<class InputIt>
    HashMap(InputIt first, InputIt last, size_type bucket_count=4)
    {
        init(std::distance(first, last) + bucket_count);
        for (; first != last; ++first)
            emplace(*first);
    }

    HashMap& operator= (const HashMap& rhs) noexcept
    {
        if (this == &rhs)
            return *this;

        if (rhs.load_factor() < EMH_MIN_LOAD_FACTOR) {
            clear(); free(_pairs); _pairs = nullptr;
            rehash(rhs._num_filled + 2);
            for (auto it = rhs.begin(); it != rhs.end(); ++it)
                insert_unique(it->first, it->second);
            return *this;
        }

        if (_num_filled)
            clearkv();

        if (_num_buckets != rhs._num_buckets) {
            free(_pairs);
            _pairs = alloc_bucket(rhs._num_buckets);
        }

        clone(rhs);
        return *this;
    }

    HashMap& operator= (HashMap&& rhs) noexcept
    {
        if (this != &rhs) {
            swap(rhs);
            rhs.clear();
        }
        return *this;
    }

    template<typename Con>
    bool operator == (const Con& rhs) const
    {
        if (size() != rhs.size())
            return false;

        for (auto it = begin(), last = end(); it != last; ++it) {
            auto oi = rhs.find(it->first);
            if (oi == rhs.end() || it->second != oi->second)
                return false;
        }
        return true;
    }

    template<typename Con>
    bool operator != (const Con& rhs) const { return !(*this == rhs); }

    ~HashMap() noexcept
    {
        if (is_triviall_destructable() && _num_filled) {
            for (auto it = cbegin(); _num_filled; ++it) {
                _num_filled --;
                it->~value_pair();
            }
        }
        free(_pairs);
        _pairs = nullptr;
    }

    void clone(const HashMap& rhs) noexcept
    {
        _hasher      = rhs._hasher;
        //_eq          = rhs._eq;

        _num_filled  = rhs._num_filled;
        _mask        = rhs._mask;
        _mlf         = rhs._mlf;
        _num_buckets = rhs._num_buckets;

        _bitmask     = decltype(_bitmask)(_pairs + EPACK_SIZE + _num_buckets);
        auto* opairs = rhs._pairs;

        if (is_copy_trivially())
            memcpy(_pairs, opairs, AllocSize(_num_buckets));
        else {
            memcpy(_pairs + _num_buckets, opairs + _num_buckets, EPACK_SIZE * sizeof(PairT) + (_num_buckets + 7) / 8 + BIT_PACK);
            for (auto it = rhs.cbegin(); it.bucket() <= _mask; ++it) {
                const auto bucket = it.bucket();
                new(_pairs + bucket) PairT(opairs[bucket]); EMH_BUCKET(_pairs, bucket) = EMH_BUCKET(opairs, bucket);
            }
        }
    }

    void swap(HashMap& rhs)
    {
        std::swap(_hasher, rhs._hasher);
        //std::swap(_eq, rhs._eq);
        std::swap(_pairs, rhs._pairs);
        std::swap(_num_buckets, rhs._num_buckets);
        std::swap(_num_filled, rhs._num_filled);
        std::swap(_mask, rhs._mask);
        std::swap(_mlf, rhs._mlf);
        std::swap(_bitmask, rhs._bitmask);
    }

    // -------------------------------------------------------------
    iterator begin() noexcept
    {
#ifdef EMH_ZERO_MOVE
        if (0 == _num_filled)
            return {this, _num_buckets};
#endif

        const auto bmask = ~(*(size_t*)_bitmask);
        if (bmask != 0)
            return {this, (size_type)CTZ(bmask)};

        iterator it(this, sizeof(bmask) * 8 - 1);
        it.init();
        return it.next();
    }

    const_iterator cbegin() const noexcept
    {
#ifdef EMH_ZERO_MOVE
        if (0 == _num_filled)
            return {this, _num_buckets};
#endif

        const auto bmask = ~(*(size_t*)_bitmask);
        if (bmask != 0)
            return {this, (size_type)CTZ(bmask)};

        iterator it(this, sizeof(bmask) * 8 - 1);
        it.init();
        return it.next();
    }

    iterator last() const
    {
        if (_num_filled == 0)
            return end();

        auto bucket = _mask;
        while (EMH_EMPTY(bucket)) bucket--;
        return {this, bucket};
    }

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

    inline iterator end() noexcept { return {this, _num_buckets}; }
    inline const_iterator cend() const { return {this, _num_buckets}; }
    inline const_iterator end() const { return cend(); }

    inline size_type size() const { return _num_filled; }
    inline bool empty() const { return _num_filled == 0; }

    inline size_type bucket_count() const { return _num_buckets; }
    inline float load_factor() const { return static_cast<float>(_num_filled) / (_mask + 1); }

    inline HashT& hash_function() const { return _hasher; }
    inline EqT& key_eq() const { return _eq; }

    inline void max_load_factor(float mlf)
    {
        if (mlf <= 0.999f && mlf > EMH_MIN_LOAD_FACTOR)
            _mlf = (uint32_t)((1 << 27) / mlf);
    }

    inline constexpr float max_load_factor() const { return (1 << 27) / (float)_mlf; }
    inline constexpr size_type max_size() const { return 1ull << (sizeof(size_type) * 8 - 1); }
    inline constexpr size_type max_bucket_count() const { return max_size(); }

    size_type bucket_main() const
    {
        auto main_size = 0;
        for (size_type bucket = 0; bucket < _num_buckets; ++bucket) {
            if (EMH_BUCKET(_pairs, bucket) == bucket)
                main_size ++;
        }
        return main_size;
    }

#if EMH_STATIS
    //Returns the bucket number where the element with key k is located.
    size_type bucket(const KeyT& key) const
    {
        const auto bucket = hash_key(key) & _mask;
        const auto next_bucket = EMH_BUCKET(_pairs, bucket);
        if (EMH_EMPTY(bucket))
            return 0;
        else if (bucket == next_bucket)
            return bucket + 1;

        const auto& bucket_key = EMH_KEY(_pairs, bucket);
        return (hash_key(bucket_key) & _mask) + 1;
    }

    //Returns the number of elements in bucket n.
    size_type bucket_size(const size_type bucket) const
    {
        if (EMH_EMPTY(bucket))
            return 0;

        auto next_bucket = EMH_BUCKET(_pairs, bucket);
        next_bucket = hash_key(EMH_KEY(_pairs, bucket)) & _mask;
        size_type bucket_size = 1;

        //iterator each item in current main bucket
        while (true) {
            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (nbucket == next_bucket) {
                break;
            }
            bucket_size++;
            next_bucket = nbucket;
        }
        return bucket_size;
    }

    size_type get_main_bucket(const size_type bucket) const
    {
        if (EMH_EMPTY(bucket))
            return INACTIVE;

        auto next_bucket = EMH_BUCKET(_pairs, bucket);
        const auto& bucket_key = EMH_KEY(_pairs, bucket);
        const auto main_bucket = hash_key(bucket_key) & _mask;
        return main_bucket;
    }

    size_type get_diss(size_type bucket, size_type next_bucket, const size_type slots) const
    {
        const int cahe_line_size = 64;
        auto pbucket = reinterpret_cast<uint64_t>(&_pairs[bucket]);
        auto pnext   = reinterpret_cast<uint64_t>(&_pairs[next_bucket]);
        if (pbucket / cahe_line_size == pnext / cahe_line_size)
            return 0;
        size_type diff = pbucket > pnext ? (pbucket - pnext) : (pnext - pbucket);
        if (diff / cahe_line_size + 1 < slots)
            return (diff / cahe_line_size + 1);
        return slots - 1;
    }

    int get_bucket_info(const size_type bucket, size_type steps[], const size_type slots) const
    {
        if (EMH_EMPTY(bucket))
            return -1;

        auto next_bucket = EMH_BUCKET(_pairs, bucket);
        if ((hash_key(EMH_KEY(_pairs, bucket)) & _mask) != bucket)
            return 0;
        else if (next_bucket == bucket)
            return 1;

        steps[get_diss(bucket, next_bucket, slots)] ++;
        size_type bucket_size = 2;
        while (true) {
            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (nbucket == next_bucket)
                break;

            steps[get_diss(nbucket, next_bucket, slots)] ++;
            bucket_size ++;
            next_bucket = nbucket;
        }

        return bucket_size;
    }

    void dump_statics(bool show_cache) const
    {
        const int slots = 128;
        size_type buckets[slots + 1] = {0};
        size_type steps[slots + 1]   = {0};
        char buff[1024 * 8];
        for (size_type bucket = 0; bucket < _num_buckets; ++bucket) {
            auto bsize = get_bucket_info(bucket, steps, slots);
            if (bsize >= 0)
                buckets[bsize] ++;
        }

        size_type sumb = 0, sums = 0, sumn = 0;
        size_type miss = 0, finds = 0, bucket_coll = 0;
        double lf = load_factor(), fk = 1.0 / exp(lf), sum_poisson = 0;
        int bsize = sprintf (buff, "============== buckets size ration ========\n");

        miss += _num_buckets - _num_filled;
        for (int i = 1, factorial = 1; i < int(sizeof(buckets) / sizeof(buckets[0])); i++) {
            double poisson = fk / factorial; factorial *= i; fk *= lf;
            if (poisson > 1e-13 && i < 20)
            sum_poisson += poisson * 100.0 * (i - 1) / i;

            const int64_t bucketsi = buckets[i];
            if (bucketsi == 0)
                continue;

            sumb += bucketsi;
            sumn += bucketsi * i;
            bucket_coll += bucketsi * (i - 1);
            finds += bucketsi * i * (i + 1) / 2;
            miss  += bucketsi * i * i;
            auto errs = (bucketsi * 1.0 * i / _num_filled - poisson) * 100 / poisson;
            bsize += sprintf(buff + bsize, "  %2d  %8ld  %0.8lf|%0.2lf%%  %2.3lf\n",
                    i, bucketsi, bucketsi * 1.0 * i / _num_filled, errs, sumn * 100.0 / _num_filled);
            if (sumn >= _num_filled)
                break;
        }

        bsize += sprintf(buff + bsize, "========== collision miss ration ===========\n");
        for (size_type i = 0; show_cache && i < sizeof(steps) / sizeof(steps[0]); i++) {
            sums += steps[i];
            if (steps[i] == 0)
                continue;
            if (steps[i] > 10)
                bsize += sprintf(buff + bsize, "  %2d  %8u  %0.2lf  %.2lf\n", (int)i, steps[i], steps[i] * 100.0 / bucket_coll, sums * 100.0 / bucket_coll);
        }

        if (sumb == 0)  return;

        bsize += sprintf(buff + bsize, "  _num_filled aver_size k.v size_kv = %u, %.2lf, %s.%s %zd\n",
                _num_filled, _num_filled * 1.0 / sumb, typeid(KeyT).name(), typeid(ValueT).name(), sizeof(PairT));

        bsize += sprintf(buff + bsize, "  collision, poisson, cache_miss hit_find|hit_miss, load_factor = %.2lf%%,%.2lf%%,%.2lf%% %.2lf|%.2lf, %.2lf\n",
                (bucket_coll * 100.0 / _num_filled), sum_poisson, (bucket_coll - steps[0]) * 100.0 / _num_filled,
                finds * 1.0 / _num_filled, miss * 1.0 / _num_buckets, _num_filled * 1.0 / _num_buckets);

        bsize += sprintf(buff + bsize, "============== buckets size end =============\n");
        buff[bsize + 1] = 0;

#ifdef EMH_LOG
        EMH_LOG << __FUNCTION__ << "|" << buff << endl;
#else
        puts(buff);
#endif
        assert(sumn == _num_filled);
        assert(sums == bucket_coll || !show_cache);
        assert(bucket_coll == buckets[0]);
    }
#endif

    // ------------------------------------------------------------
    template<typename Key = KeyT>
    inline iterator find(const Key& key, size_t key_hash) noexcept
    {
        return {this, find_filled_hash(key, key_hash)};
    }

    template<typename Key = KeyT>
    inline const_iterator find(const Key& key, size_t key_hash) const noexcept
    {
        return {this, find_filled_hash(key, key_hash)};
    }

    template<typename Key=KeyT>
    inline iterator find(const Key& key) noexcept
    {
        return {this, find_filled_bucket(key)};
    }

    template<typename Key = KeyT>
    inline const_iterator find(const Key& key) const noexcept
    {
        return {this, find_filled_bucket(key)};
    }

    template<typename Key = KeyT>
    ValueT& at(const KeyT& key)
    {
        const auto bucket = find_filled_bucket(key);
        //throw
        return EMH_VAL(_pairs, bucket);
    }

    template<typename Key = KeyT>
    const ValueT& at(const KeyT& key) const
    {
        const auto bucket = find_filled_bucket(key);
        //throw
        return EMH_VAL(_pairs, bucket);
    }

    template<typename Key = KeyT>
    inline bool contains(const Key& key) const noexcept
    {
        return find_filled_bucket(key) != _num_buckets;
    }

    template<typename Key = KeyT>
    inline size_type count(const Key& key) const noexcept
    {
        return find_filled_bucket(key) != _num_buckets ? 1 : 0;
    }

    template<typename Key = KeyT>
    std::pair<iterator, iterator> equal_range(const Key& key) const noexcept
    {
        const auto found = {this, find_filled_bucket(key), true};
        if (found.bucket() == _num_buckets)
            return { found, found };
        else
            return { found, std::next(found) };
    }

    template<typename K=KeyT>
    std::pair<const_iterator, const_iterator> equal_range(const K& key) const
    {
        const auto found = {this, find_filled_bucket(key), true};
        if (found.bucket() == _num_buckets)
            return { found, found };
        else
            return { found, std::next(found) };
    }

    void merge(HashMap& rhs)
    {
        if (empty()) {
            *this = std::move(rhs);
            return;
        }

        for (auto rit = rhs.begin(); rit != rhs.end(); ) {
            auto fit = find(rit->first);
            if (fit.bucket() == _num_buckets) {
                insert_unique(rit->first, std::move(rit->second));
                rit = rhs.erase(rit);
            } else {
                ++rit;
            }
        }
    }

#ifdef EMH_EXT
    bool try_get(const KeyT& key, ValueT& val) const noexcept
    {
        const auto bucket = find_filled_bucket(key);
        const auto found = bucket != _num_buckets;
        if (found) {
            val = EMH_VAL(_pairs, bucket);
        }
        return found;
    }

    /// Returns the matching ValueT or nullptr if k isn't found.
    ValueT* try_get(const KeyT& key) noexcept
    {
        const auto bucket = find_filled_bucket(key);
        return bucket == _num_buckets ? nullptr : &EMH_VAL(_pairs, bucket);
    }

    /// Const version of the above
    ValueT* try_get(const KeyT& key) const noexcept
    {
        const auto bucket = find_filled_bucket(key);
        return bucket == _num_buckets ? nullptr : &EMH_VAL(_pairs, bucket);
    }

    /// Convenience function.
    ValueT get_or_return_default(const KeyT& key) const noexcept
    {
        const auto bucket = find_filled_bucket(key);
        return bucket == _num_buckets ? ValueT() : EMH_VAL(_pairs, bucket);
    }
#endif

    // -----------------------------------------------------
    template<typename K = KeyT, typename V = ValueT>
    std::pair<iterator, bool> do_assign(K&& key, V&& val)
    {
        reserve(_num_filled);

        bool isempty;
        const auto bucket = find_or_allocate(key, isempty);
        if (isempty) {
            EMH_NEW(std::forward<K>(key), std::forward<V>(val), bucket);
        } else {
            EMH_VAL(_pairs, bucket) = std::move(val);
        }
        return { {this, bucket}, isempty };
    }

    std::pair<iterator, bool> do_insert(const value_type& value)
    {
        bool isempty;
        const auto bucket = find_or_allocate(value.first, isempty);
        if (isempty) {
            EMH_NEW(value.first, value.second, bucket);
        }
        return { {this, bucket}, isempty };
    }

    std::pair<iterator, bool> do_insert(value_type&& value)
    {
        bool isempty;
        const auto bucket = find_or_allocate(value.first, isempty);
        if (isempty) {
            EMH_NEW(std::move(value.first), std::move(value.second), bucket);
        }
        return { {this, bucket}, isempty };
    }

    template<typename K = KeyT, typename V = ValueT>
    std::pair<iterator, bool> do_insert(K&& key, V&& val)
    {
        bool isempty;
        const auto bucket = find_or_allocate(key, isempty);
        if (isempty) {
            EMH_NEW(std::forward<K>(key), std::forward<V>(val), bucket);
        }
        return { {this, bucket}, isempty };
    }

    std::pair<iterator, bool> insert(const value_type& value)
    {
        check_expand_need();
        return do_insert(value);
    }

    std::pair<iterator, bool> insert(value_type&& value)
    {
        check_expand_need();
        return do_insert(std::move(value));
    }

    void insert(std::initializer_list<value_type> ilist)
    {
        reserve(ilist.size() + _num_filled);
        for (auto it = ilist.begin(); it != ilist.end(); ++it)
            do_insert(*it);
    }

    template <typename Iter>
    void insert(Iter first, Iter last)
    {
        reserve(std::distance(first, last) + _num_filled);
        for (auto it = first; it != last; ++it)
            do_insert(it->first, it->second);
    }

#if 0
    template <typename Iter>
    void insert_unique(Iter begin, Iter end)
    {
        reserve(std::distance(begin, end) + _num_filled);
        for (; begin != end; ++begin)
            do_insert_unqiue(*begin);
    }
#endif

    template<typename K, typename V>
    inline size_type insert_unique(K&& key, V&& val)
    {
        return do_insert_unqiue(std::forward<K>(key), std::forward<V>(val));
    }

    inline size_type insert_unique(value_type&& value)
    {
        return do_insert_unqiue(std::move(value.first), std::move(value.second));
    }

    inline size_type insert_unique(const value_type& value)
    {
        return do_insert_unqiue(value.first, value.second);
    }

    template<typename K, typename V>
    size_type do_insert_unqiue(K&& key, V&& val)
    {
        check_expand_need();
        auto bucket = find_unique_bucket(key);
        EMH_NEW(std::forward<K>(key), std::forward<V>(val), bucket);
        return bucket;
    }

    std::pair<iterator, bool> insert_or_assign(const KeyT& key, ValueT&& val) { return do_assign(key, std::forward<ValueT>(val)); }
    std::pair<iterator, bool> insert_or_assign(KeyT&& key, ValueT&& val) { return do_assign(std::move(key), std::forward<ValueT>(val)); }

    template <typename... Args>
    std::pair<iterator, bool> emplace(Args&&... args) noexcept
    {
        check_expand_need();
        return do_insert(std::forward<Args>(args)...);
    }

    template <class... Args>
    iterator emplace_hint(const_iterator hint, Args&&... args)
    {
        (void)hint;
        check_expand_need();
        return do_insert(std::forward<Args>(args)...).first;
    }

    template<class... Args>
    std::pair<iterator, bool> try_emplace(const KeyT& key, Args&&... args)
    {
        check_expand_need();
        return do_insert(key, std::forward<Args>(args)...);
    }

    template<class... Args>
    std::pair<iterator, bool> try_emplace(KeyT&& key, Args&&... args)
    {
        check_expand_need();
        return do_insert(std::forward<KeyT>(key), std::forward<Args>(args)...);
    }

    template <class... Args>
    size_type emplace_unique(Args&&... args) noexcept
    {
        return insert_unique(std::forward<Args>(args)...);
    }

    /* Check if inserting a new value rather than overwriting an old entry */
    ValueT& operator[](const KeyT& key) noexcept
    {
        check_expand_need();

        bool isempty;
        const auto bucket = find_or_allocate(key, isempty);
        if (isempty) {
            EMH_NEW(key, std::move(ValueT()), bucket);
        }

        return EMH_VAL(_pairs, bucket);
    }

    ValueT& operator[](KeyT&& key) noexcept
    {
        check_expand_need();

        bool isempty;
        const auto bucket = find_or_allocate(key, isempty);
        if (isempty) {
            EMH_NEW(std::move(key), std::move(ValueT()), bucket);
        }

        return EMH_VAL(_pairs, bucket);
    }

    // -------------------------------------------------------
    /// Erase an element from the hash table.
    /// return 0 if element was not found
    template<typename Key = KeyT>
    size_type erase(const Key& key)
    {
        const auto bucket = erase_key(key);
        if (bucket == INACTIVE)
            return 0;

        clear_bucket(bucket);
        return 1;
    }

    //iterator erase const_iterator
    iterator erase(const_iterator cit)
    {
        iterator it(cit);
        return erase(it);
    }

    /// Erase an element typedef an iterator.
    /// Returns an iterator to the next element (or end()).
    iterator erase(iterator it)
    {
        const auto bucket = erase_bucket(it._bucket);
        clear_bucket(bucket);
        if (bucket == it._bucket) {
            return ++it;
        } else {
            //erase main bucket as next
            it.clear(bucket);
            return it;
        }
    }

    /// Erase an element typedef an iterator without return next iterator
    void _erase(const_iterator it)
    {
        const auto bucket = erase_bucket(it._bucket);
        clear_bucket(bucket);
    }

    template<typename Pred>
    size_type erase_if(Pred pred)
    {
        auto old_size = size();
        for (auto it = begin(), last = end(); it != last; ) {
            if (pred(*it))
                it = erase(it);
            else
                ++it;
        }
        return old_size - size();
    }

    static constexpr bool is_triviall_destructable()
    {
#if __cplusplus >= 201402L || _MSC_VER > 1600
        return !(std::is_trivially_destructible<KeyT>::value && std::is_trivially_destructible<ValueT>::value);
#else
        return !(std::is_pod<KeyT>::value && std::is_pod<ValueT>::value);
#endif
    }

    static constexpr bool is_copy_trivially()
    {
#if __cplusplus >= 201402L || _MSC_VER > 1600
        return (std::is_trivially_copyable<KeyT>::value && std::is_trivially_copyable<ValueT>::value);
#else
        return (std::is_pod<KeyT>::value && std::is_pod<ValueT>::value);
#endif
    }

    void clearkv()
    {
        if (is_triviall_destructable()) {
            auto it = cbegin(); it.init();
            for (; _num_filled; ++it)
                clear_bucket(it.bucket());
        }
    }

    /// Remove all elements, keeping full capacity.
    void clear()
    {
        if (!is_triviall_destructable() && _num_filled) {
            memset(_bitmask, 0xFFFFFFFF, (_num_buckets + 7) / 8);
            if (_num_buckets < 8) _bitmask[0] = (1 << _num_buckets) - 1;
        }
        else if (_num_filled)
            clearkv();

        //EMH_BUCKET(_pairs, _num_buckets) = 0; //_last
        _num_filled = 0;
    }

    void shrink_to_fit()
    {
        rehash(_num_filled + 1);
    }

    /// Make room for this many elements
    bool reserve(uint64_t num_elems)
    {
        const auto required_buckets = (num_elems * _mlf >> 27);
        if (EMH_LIKELY(required_buckets < _num_buckets))
            return false;

#if EMH_HIGH_LOAD
        if (required_buckets < 64 && _num_filled < _num_buckets)
            return false;
#endif

#if EMH_STATIS
        if (_num_filled > EMH_STATIS) dump_statics(true);
#endif
        rehash(required_buckets + 2);
        return true;
    }

    void rehash(uint64_t required_buckets)
    {
        if (required_buckets < _num_filled)
            return;

        uint64_t buckets = _num_filled > (1u << 16) ? (1u << 16) : 2u;
        while (buckets < required_buckets) { buckets *= 2; }

        // no need alloc large bucket for small key sizeof(KeyT) < sizeof(int).
        // set small a max_load_factor, insert/reserve() will fail and introduce rehash issiue TODO: dothing ?
        if (sizeof(KeyT) < sizeof(size_type) && buckets >= (1ul << (2 * 8)))
            buckets = 2ul << (sizeof(KeyT) * 8);

        assert(buckets < max_size() && buckets > _num_filled);
        //TODO: throwOverflowError

        auto num_buckets = (size_type)buckets;
        auto old_num_filled = _num_filled;
        auto old_mask  = _num_buckets - 1;
        auto old_pairs = _pairs;
        auto* obmask   = _bitmask;

        _num_filled  = 0;
        _num_buckets = num_buckets;
        _mask        = num_buckets - 1;

        _pairs = alloc_bucket(_num_buckets);
        memset((char*)(_pairs + _num_buckets), 0, sizeof(PairT) * EPACK_SIZE);

        _bitmask     = decltype(_bitmask)(_pairs + EPACK_SIZE + num_buckets);

        const auto mask_byte = (num_buckets + 7) / 8;
        memset(_bitmask, 0xFFFFFFFF, mask_byte);
        memset(((char*)_bitmask) + mask_byte, 0, BIT_PACK);
        if (num_buckets < 8)
            _bitmask[0] = (1 << num_buckets) - 1;

        //for (size_type src_bucket = 0; _num_filled < old_num_filled; src_bucket++) {
        for (size_type src_bucket = old_mask; _num_filled < old_num_filled; src_bucket --) {
            if (obmask[src_bucket / MASK_BIT] & (EMH_MASK(src_bucket)))
                continue;

            auto& key = EMH_KEY(old_pairs, src_bucket);
            const auto bucket = find_unique_bucket(key);
            EMH_NEW(std::move(key), std::move(EMH_VAL(old_pairs, src_bucket)), bucket);
            if (is_triviall_destructable())
                old_pairs[src_bucket].~PairT();
        }

#if EMH_REHASH_LOG
        if (_num_filled > EMH_REHASH_LOG) {
            auto mbucket = bucket_main();
            char buff[255] = {0};
            sprintf(buff, "    _num_filled/collision/main/K.V/pack/ = %u/%.2lf%%(%.2lf%%)/%s.%s/%zd",
                    _num_filled, 200.0f * (_num_filled - mbucket) / _mask,  100.0f * mbucket / _mask,
                    typeid(KeyT).name(), typeid(ValueT).name(), sizeof(_pairs[0]));
#ifdef EMH_LOG
            static size_t ihashs = 0;
            EMH_LOG << "rhash_nums = " << ihashs ++ << "|" <<__FUNCTION__ << "|" << buff << endl;
#else
            puts(buff);
#endif
        }
#endif

        free(old_pairs);
        assert(old_num_filled == _num_filled);
    }

private:
    // Can we fit another element?
    inline bool check_expand_need()
    {
        return reserve(_num_filled);
    }

    void clear_bucket(size_type bucket)
    {
        EMH_CLS(bucket);
        _num_filled--;
        if (is_triviall_destructable())
            _pairs[bucket].~PairT();
    }

#if 1
    //template<typename UType, typename std::enable_if<std::is_integral<UType>::value, size_type>::type = 0>
    template<typename UType>
    size_type erase_key(const UType& key)
    {
        const auto bucket = hash_key(key) & _mask;
        if (EMH_EMPTY(bucket))
            return INACTIVE;

        auto next_bucket = EMH_BUCKET(_pairs, bucket);
        const auto eqkey = _eq(key, EMH_KEY(_pairs, bucket));
        if (eqkey) {
            if (next_bucket == bucket)
                return bucket;

            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (is_copy_trivially())
                EMH_PKV(_pairs, bucket) = EMH_PKV(_pairs, next_bucket);
            else
                EMH_PKV(_pairs, bucket).swap(EMH_PKV(_pairs, next_bucket));

            EMH_BUCKET(_pairs, bucket) = (nbucket == next_bucket) ? bucket : nbucket;
            return next_bucket;
        } else if (next_bucket == bucket)
            return INACTIVE;
        /* else if (EMH_UNLIKELY(bucket != hash_key(EMH_KEY(_pairs, bucket)) & _mask))
            return INACTIVE;
        */

        auto prev_bucket = bucket;
        while (true) {
            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (_eq(key, EMH_KEY(_pairs, next_bucket))) {
                EMH_BUCKET(_pairs, prev_bucket) = (nbucket == next_bucket) ? prev_bucket : nbucket;
                return next_bucket;
            }

            if (nbucket == next_bucket)
                break;
            prev_bucket = next_bucket;
            next_bucket = nbucket;
        }

        return INACTIVE;
    }
#else
    template<typename UType, typename std::enable_if<!std::is_integral<UType>::value, size_type>::type = 0>
    size_type erase_key(const UType& key)
    {
        const auto bucket = hash_key(key) & _mask;
        if (EMH_EMPTY(bucket))
            return INACTIVE;

        auto next_bucket = EMH_BUCKET(_pairs, bucket);
        if (next_bucket == bucket)
            return _eq(key, EMH_KEY(_pairs, bucket)) ? bucket : INACTIVE;
//        else if (bucket != hash_key(EMH_KEY(_pairs, bucket)))
//            return INACTIVE;

        //find erase key and swap to last bucket
        size_type prev_bucket = bucket, find_bucket = INACTIVE;
        next_bucket = bucket;
        while (true) {
            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (_eq(key, EMH_KEY(_pairs, next_bucket))) {
                find_bucket = next_bucket;
                if (nbucket == next_bucket) {
                    EMH_BUCKET(_pairs, prev_bucket) = prev_bucket;
                    break;
                }
            }
            if (nbucket == next_bucket) {
                if (find_bucket != INACTIVE) {
                    EMH_PKV(_pairs, find_bucket).swap(EMH_PKV(_pairs, nbucket));
//                    EMH_PKV(_pairs, find_bucket) = EMH_PKV(_pairs, nbucket);
                    EMH_BUCKET(_pairs, prev_bucket) = prev_bucket;
                    find_bucket = nbucket;
                }
                break;
            }
            prev_bucket = next_bucket;
            next_bucket = nbucket;
        }

        return find_bucket;
    }
#endif

    size_type erase_bucket(const size_type bucket)
    {
        const auto next_bucket = EMH_BUCKET(_pairs, bucket);
        const auto main_bucket = hash_key(EMH_KEY(_pairs, bucket)) & _mask;
        if (bucket == main_bucket) {
            if (bucket != next_bucket) {
                const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
                if (is_copy_trivially())
                    EMH_PKV(_pairs, bucket) = EMH_PKV(_pairs, next_bucket);
                else
                    EMH_PKV(_pairs, bucket).swap(EMH_PKV(_pairs, next_bucket));
                EMH_BUCKET(_pairs, bucket) = (nbucket == next_bucket) ? bucket : nbucket;
            }
            return next_bucket;
        }

        const auto prev_bucket = find_prev_bucket(main_bucket, bucket);
        EMH_BUCKET(_pairs, prev_bucket) = (bucket == next_bucket) ? prev_bucket : next_bucket;
        return bucket;
    }

    // Find the bucket with this key, or return bucket size
    template<typename K = KeyT>
    size_type find_filled_hash(const K& key, const size_t key_hash) const
    {
        const auto bucket = key_hash & _mask;
        if (EMH_EMPTY(bucket))
            return _num_buckets;

        auto next_bucket = bucket;
        while (true) {
            if (_eq(key, EMH_KEY(_pairs, next_bucket)))
                return next_bucket;

            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (nbucket == next_bucket)
                break;
            next_bucket = nbucket;
        }

        return _num_buckets;
    }

    // Find the bucket with this key, or return bucket size
    template<typename K = KeyT>
    size_type find_filled_bucket(const K& key) const
    {
        const auto bucket = hash_key(key) & _mask;
        if (EMH_EMPTY(bucket))
            return _num_buckets;

        auto next_bucket = bucket;
//        else if (bucket != (hash_key(bucket_key) & _mask))
//            return _num_buckets;

        while (true) {
            if (_eq(key, EMH_KEY(_pairs, next_bucket)))
                return next_bucket;

            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (nbucket == next_bucket)
                return _num_buckets;
            next_bucket = nbucket;
        }

        return 0;
    }

    //kick out bucket and find empty to occpuy
    //it will break the orgin link and relnik again.
    //before: main_bucket-->prev_bucket --> bucket   --> next_bucket
    //atfer : main_bucket-->prev_bucket --> (removed)--> new_bucket--> next_bucket
    size_type kickout_bucket(const size_type kmain, const size_type kbucket)
    {
        const auto next_bucket = EMH_BUCKET(_pairs, kbucket);
        const auto new_bucket  = find_empty_bucket(next_bucket, kbucket);
        const auto prev_bucket = find_prev_bucket(kmain, kbucket);
        new(_pairs + new_bucket) PairT(std::move(_pairs[kbucket]));
        if (is_triviall_destructable())
            _pairs[kbucket].~PairT();

        if (next_bucket == kbucket)
            EMH_BUCKET(_pairs, new_bucket) = new_bucket;
        EMH_BUCKET(_pairs, prev_bucket) = new_bucket;

        EMH_SET(new_bucket);
        return kbucket;
    }

/*
** inserts a new key into a hash table; first check whether key's main
** bucket/position is free. If not, check whether colliding node/bucket is in its main
** position or not: if it is not, move colliding bucket to an empty place and
** put new key in its main position; otherwise (colliding bucket is in its main
** position), new key goes to an empty position. ***/

    template<typename K=KeyT>
    size_type find_or_allocate(const K& key, bool& isempty)
    {
        const auto bucket = hash_key(key) & _mask;
        const auto& bucket_key = EMH_KEY(_pairs, bucket);
        if (EMH_EMPTY(bucket)) {
            isempty = true;
            return bucket;
        }
        else if (_eq(key, bucket_key)) {
            isempty = false;
            return bucket;
        }

        isempty = true;
        auto next_bucket = EMH_BUCKET(_pairs, bucket);
        //check current bucket_key is in main bucket or not
        const auto kmain_bucket = hash_key(bucket_key) & _mask;
        if (kmain_bucket != bucket)
            return kickout_bucket(kmain_bucket, bucket);
        else if (next_bucket == bucket)
            return EMH_BUCKET(_pairs, next_bucket) = find_empty_bucket(next_bucket, bucket);

#if EMH_LRU_SET
        auto prev_bucket = bucket;
#endif
        //find next linked bucket and check key, if lru is set then swap current key with prev_bucket
        while (true) {
            if (EMH_UNLIKELY(_eq(key, EMH_KEY(_pairs, next_bucket)))) {
                isempty = false;
#if EMH_LRU_SET
                EMH_PKV(_pairs, next_bucket).swap(EMH_PKV(_pairs, prev_bucket));
                return prev_bucket;
#else
                return next_bucket;
#endif
            }

#if EMH_LRU_SET
            prev_bucket = next_bucket;
#endif

            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (nbucket == next_bucket)
                break;
            next_bucket = nbucket;
        }

        //find a new empty and link it to tail, TODO link after main bucket?
        const auto new_bucket = find_empty_bucket(next_bucket, bucket);// : find_empty_bucket(next_bucket);
        return EMH_BUCKET(_pairs, next_bucket) = new_bucket;
    }

    // key is not in this map. Find a place to put it.
    size_type find_empty_bucket(const size_type bucket_from, const size_type main_bucket)
    {
#if EMH_ITER_SAFE
        const auto boset = bucket_from % 8;
        auto* const align = (uint8_t*)_bitmask + bucket_from / 8;(void)main_bucket;
        size_t bmask; memcpy(&bmask, align + 0, sizeof(bmask)); bmask >>= boset;// bmask |= ((size_t)align[8] << (SIZE_BIT - boset));
        if (EMH_LIKELY(bmask != 0))
            return bucket_from + CTZ(bmask);
#else
        const auto boset  = main_bucket % 8;
        auto* const align = (uint8_t*)_bitmask + main_bucket / 8; (void)bucket_from;
        const size_t bmask  = (*(size_t*)(align) >> boset);// & 0xF0F0F0F0FF0FF0FFull;//
        if (EMH_LIKELY(bmask != 0))
            return main_bucket + CTZ(bmask);
#endif

        const auto qmask = _mask / SIZE_BIT;
        if (0) {
            const size_type step = (main_bucket - SIZE_BIT / 4) & qmask;
            const auto bmask3 = *((size_t*)_bitmask + step);
            if (bmask3 != 0)
                return step * SIZE_BIT + CTZ(bmask3);
        }

        //auto next_bucket = (bucket_from + 0 * SIZE_BIT) & qmask;
        auto& last = EMH_BUCKET(_pairs, _num_buckets);
        for (size_type offset = 1; ; offset += 1) {
            last &= qmask;
            const auto bmask2 = *((size_t*)_bitmask + last);
            if (bmask2 != 0)
                return last * SIZE_BIT + CTZ(bmask2);
#if 1
            const auto next1 = (qmask / 2 + last) & qmask;
            const auto bmask1 = *((size_t*)_bitmask + next1);
            if (bmask1 != 0) {
                last = next1;
                return next1 * SIZE_BIT + CTZ(bmask1);
            }
            last += 1;
#else
            next_bucket += offset < 10 ? 1 + SIZE_BIT * offset : 1 + qmask / 32;
            if (next_bucket >= qmask) {
                next_bucket += 1;
                next_bucket &= qmask;
            }

            const auto bmask1 = *((size_t*)_bitmask + next_bucket);
            if (bmask1 != 0) {
                last = next_bucket;
                return next_bucket * SIZE_BIT + CTZ(bmask1);
            }
#endif
        }

        return 0;
    }

    // key is not in this map. Find a place to put it.
    size_type find_unique_empty(const size_type bucket_from)
    {
        const auto boset = bucket_from % 8;
        auto* const align = (uint8_t*)_bitmask + bucket_from / 8;

#if EMH_ITER_SAFE
        size_t bmask; memcpy(&bmask, align + 0, sizeof(bmask)); bmask >>= boset;
#else
        const auto bmask = (*(size_t*)(align) >> boset); //maybe not aligned and warning
#endif
        if (EMH_LIKELY(bmask != 0))
            return bucket_from + CTZ(bmask);

        const auto qmask = _mask / SIZE_BIT;
        for (auto last = (bucket_from + _mask) & qmask; ;) {
            const auto bmask2 = *((size_t*)_bitmask + last);// & 0xF0F0F0F0FF0FF0FFull;
            if (EMH_LIKELY(bmask2 != 0))
                return last * SIZE_BIT + CTZ(bmask2);
            last = (last + 1) & qmask;
        }

        return 0;
    }

    size_type find_last_bucket(size_type main_bucket) const
    {
        auto next_bucket = EMH_BUCKET(_pairs, main_bucket);
        if (next_bucket == main_bucket)
            return main_bucket;

        while (true) {
            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (nbucket == next_bucket)
                return next_bucket;
            next_bucket = nbucket;
        }
    }

    size_type find_prev_bucket(size_type main_bucket, const size_type bucket) const
    {
        auto next_bucket = EMH_BUCKET(_pairs, main_bucket);
        if (next_bucket == bucket)
            return main_bucket;

        while (true) {
            const auto nbucket = EMH_BUCKET(_pairs, next_bucket);
            if (nbucket == bucket)
                return next_bucket;
            next_bucket = nbucket;
        }
    }

    size_type find_unique_bucket(const KeyT& key)
    {
        const size_type bucket = hash_key(key) & _mask;
        if (EMH_EMPTY(bucket))
            return bucket;

        //check current bucket_key is in main bucket or not
        const auto kmain_bucket = hash_key(EMH_KEY(_pairs, bucket)) & _mask;
        if (EMH_UNLIKELY(kmain_bucket != bucket))
            return kickout_bucket(kmain_bucket, bucket);

        auto next_bucket = EMH_BUCKET(_pairs, bucket);
        if (next_bucket != bucket)
            next_bucket = find_last_bucket(next_bucket);

        //find a new empty and link it to tail
        return EMH_BUCKET(_pairs, next_bucket) = find_empty_bucket(next_bucket, bucket);
    }

#if EMH_INT_HASH
    static constexpr uint64_t KC = UINT64_C(11400714819323198485);
    inline static uint64_t hash64(uint64_t key)
    {
#if __SIZEOF_INT128__ && EMH_INT_HASH == 1
        __uint128_t r = key; r *= KC;
        return (uint64_t)(r >> 64) + (uint64_t)r;
#elif EMH_INT_HASH == 2
        //MurmurHash3Mixer
        uint64_t h = key;
        h ^= h >> 33;
        h *= 0xff51afd7ed558ccd;
        h ^= h >> 33;
        h *= 0xc4ceb9fe1a85ec53;
        h ^= h >> 33;
        return h;
#elif _WIN64 && EMH_INT_HASH == 1
        uint64_t high;
        return _umul128(key, KC, &high) + high;
#elif EMH_INT_HASH == 3
        auto ror  = (key >> 32) | (key << 32);
        auto low  = key * 0xA24BAED4963EE407ull;
        auto high = ror * 0x9FB21C651E98DF25ull;
        auto mix  = low + high;
        return mix;
#elif EMH_INT_HASH == 1
        uint64_t r = key * UINT64_C(0xca4bcaa75ec3f625);
        return (r >> 32) + r;
#elif EMH_WYHASH64
        return wyhash64(key, KC);
#else
        uint64_t x = key;
        x = (x ^ (x >> 30)) * UINT64_C(0xbf58476d1ce4e5b9);
        x = (x ^ (x >> 27)) * UINT64_C(0x94d049bb133111eb);
        x = x ^ (x >> 31);
        return x;
#endif
    }
#endif

    template<typename UType, typename std::enable_if<std::is_integral<UType>::value, size_type>::type = 0>
    inline size_type hash_key(const UType key) const
    {
#if EMH_INT_HASH
        return hash64(key);
#elif EMH_IDENTITY_HASH
        return key + (key >> 24);
#else
        return (size_type)_hasher(key);
#endif
    }

    template<typename UType, typename std::enable_if<std::is_same<UType, std::string>::value, size_type>::type = 0>
    inline size_type hash_key(const UType& key) const
    {
#if EMH_WY_HASH
        return wyhash(key.data(), key.size(), 0);
#else
        return (size_type)_hasher(key);
#endif
    }

    template<typename UType, typename std::enable_if<!std::is_integral<UType>::value && !std::is_same<UType, std::string>::value, size_type>::type = 0>
    inline size_type hash_key(const UType& key) const
    {
        return (size_type)_hasher(key);
    }

private:
    uint8_t* _bitmask;
    PairT*    _pairs;
    HashT     _hasher;
    EqT       _eq;
    size_type _mask;
    size_type _num_buckets;

    size_type _num_filled;
    uint32_t  _mlf;

private:
    static constexpr uint32_t BIT_PACK = sizeof(uint64_t);
    static constexpr uint32_t MASK_BIT = sizeof(_bitmask[0]) * 8;
    static constexpr uint32_t SIZE_BIT = sizeof(size_t) * 8;
    static constexpr uint32_t EPACK_SIZE = sizeof(PairT) >= sizeof(size_t) == 0 ? 1 : 2; // > 1
};
}
// namespace emhash7
#if __cplusplus >= 201103L
//template <class Key, class Val> using ehmap7 = emhash7::HashMap<Key, Val, std::hash<Key>, std::equal_to<Key>>;
#endif

//TODO
//2. improve rehash and find miss performance(reduce peak memory)
//3. dump or Serialization interface
//4. node hash map support
//5. load_factor > 1.0 && add grow ration
//... https://godbolt.org/