// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___SPLIT_BUFFER
#define _LIBCPP___SPLIT_BUFFER

#include <__algorithm/max.h>
#include <__algorithm/move.h>
#include <__algorithm/move_backward.h>
#include <__config>
#include <__iterator/distance.h>
#include <__iterator/iterator_traits.h>
#include <__iterator/move_iterator.h>
#include <__memory/allocate_at_least.h>
#include <__memory/allocator.h>
#include <__memory/allocator_traits.h>
#include <__memory/compressed_pair.h>
#include <__memory/pointer_traits.h>
#include <__memory/swap_allocator.h>
#include <__type_traits/add_lvalue_reference.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/integral_constant.h>
#include <__type_traits/is_nothrow_default_constructible.h>
#include <__type_traits/is_nothrow_move_assignable.h>
#include <__type_traits/is_nothrow_move_constructible.h>
#include <__type_traits/is_swappable.h>
#include <__type_traits/is_trivially_destructible.h>
#include <__type_traits/remove_reference.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <cstddef>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>


_LIBCPP_BEGIN_NAMESPACE_STD

// __split_buffer allocates a contiguous chunk of memory and stores objects in the range [__begin_, __end_).
// It has uninitialized memory in the ranges  [__first_, __begin_) and [__end_, __end_cap_.first()). That allows
// it to grow both in the front and back without having to move the data.

template <class _Tp, class _Allocator = allocator<_Tp> >
struct __split_buffer
{
public:
  using value_type      = _Tp;
  using allocator_type  = _Allocator;
  using __alloc_rr      = __libcpp_remove_reference_t<allocator_type>;
  using __alloc_traits  = allocator_traits<__alloc_rr>;
  using reference       = value_type&;
  using const_reference = const value_type&;
  using size_type       = typename __alloc_traits::size_type;
  using difference_type = typename __alloc_traits::difference_type;
  using pointer         = typename __alloc_traits::pointer;
  using const_pointer   = typename __alloc_traits::const_pointer;
  using iterator        = pointer;
  using const_iterator  = const_pointer;

  pointer __first_;
  pointer __begin_;
  pointer __end_;
  __compressed_pair<pointer, allocator_type> __end_cap_;

  using __alloc_ref       = __add_lvalue_reference_t<allocator_type>;
  using __alloc_const_ref = __add_lvalue_reference_t<allocator_type>;

  __split_buffer(const __split_buffer&) = delete;
  __split_buffer& operator=(const __split_buffer&) = delete;

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __split_buffer()
      _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
      : __first_(nullptr), __begin_(nullptr), __end_(nullptr), __end_cap_(nullptr, __default_init_tag()) {}

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit __split_buffer(__alloc_rr& __a)
      : __first_(nullptr), __begin_(nullptr), __end_(nullptr), __end_cap_(nullptr, __a) {}

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit __split_buffer(const __alloc_rr& __a)
      : __first_(nullptr), __begin_(nullptr), __end_(nullptr), __end_cap_(nullptr, __a) {}

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
  __split_buffer(size_type __cap, size_type __start, __alloc_rr& __a);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __split_buffer(__split_buffer&& __c)
      _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __split_buffer(__split_buffer&& __c, const __alloc_rr& __a);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __split_buffer& operator=(__split_buffer&& __c)
      _NOEXCEPT_((__alloc_traits::propagate_on_container_move_assignment::value &&
                  is_nothrow_move_assignable<allocator_type>::value) ||
                 !__alloc_traits::propagate_on_container_move_assignment::value);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI ~__split_buffer();

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __alloc_rr& __alloc() _NOEXCEPT { return __end_cap_.second(); }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const __alloc_rr& __alloc() const _NOEXCEPT {
    return __end_cap_.second();
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI pointer& __end_cap() _NOEXCEPT { return __end_cap_.first(); }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const pointer& __end_cap() const _NOEXCEPT {
    return __end_cap_.first();
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __begin_; }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __begin_; }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __end_; }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __end_; }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void clear() _NOEXCEPT { __destruct_at_end(__begin_); }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type size() const {
    return static_cast<size_type>(__end_ - __begin_);
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool empty() const { return __end_ == __begin_; }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type capacity() const {
    return static_cast<size_type>(__end_cap() - __first_);
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type __front_spare() const {
    return static_cast<size_type>(__begin_ - __first_);
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type __back_spare() const {
    return static_cast<size_type>(__end_cap() - __end_);
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI reference front() { return *__begin_; }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_reference front() const { return *__begin_; }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI reference back() { return *(__end_ - 1); }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_reference back() const { return *(__end_ - 1); }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void reserve(size_type __n);
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void shrink_to_fit() _NOEXCEPT;
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void push_front(const_reference __x);
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void push_back(const_reference __x);
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void push_front(value_type&& __x);
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void push_back(value_type&& __x);

  template <class... _Args>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void emplace_back(_Args&&... __args);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void pop_front() { __destruct_at_begin(__begin_ + 1); }
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void pop_back() { __destruct_at_end(__end_ - 1); }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __construct_at_end(size_type __n);
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __construct_at_end(size_type __n, const_reference __x);

  template <class _InputIter>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
      __enable_if_t<__is_exactly_cpp17_input_iterator<_InputIter>::value>
      __construct_at_end(_InputIter __first, _InputIter __last);

  template <class _ForwardIterator>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
      __enable_if_t<__is_cpp17_forward_iterator<_ForwardIterator>::value>
      __construct_at_end(_ForwardIterator __first, _ForwardIterator __last);

  template <class _Iterator, class _Sentinel>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
  void __construct_at_end_with_sentinel(_Iterator __first, _Sentinel __last);

  template <class _Iterator>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
  void __construct_at_end_with_size(_Iterator __first, size_type __n);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_begin(pointer __new_begin) {
    __destruct_at_begin(__new_begin, is_trivially_destructible<value_type>());
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_begin(pointer __new_begin, false_type);
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_begin(pointer __new_begin, true_type);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_end(pointer __new_last) _NOEXCEPT {
    __destruct_at_end(__new_last, false_type());
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_end(pointer __new_last, false_type) _NOEXCEPT;
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_end(pointer __new_last, true_type) _NOEXCEPT;

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void swap(__split_buffer& __x)
      _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value || __is_nothrow_swappable<__alloc_rr>::value);

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool __invariants() const;

private:
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__split_buffer& __c, true_type)
      _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value) {
    __alloc() = _VSTD::move(__c.__alloc());
  }

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__split_buffer&, false_type) _NOEXCEPT {}

  struct _ConstructTransaction {
    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit _ConstructTransaction(
        pointer* __p, size_type __n) _NOEXCEPT
        : __pos_(*__p),
          __end_(*__p + __n),
          __dest_(__p) {}

    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI ~_ConstructTransaction() { *__dest_ = __pos_; }

    pointer __pos_;
    const pointer __end_;

  private:
    pointer* __dest_;
  };
};

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
bool
__split_buffer<_Tp, _Allocator>::__invariants() const
{
    if (__first_ == nullptr)
    {
        if (__begin_ != nullptr)
            return false;
        if (__end_ != nullptr)
            return false;
        if (__end_cap() != nullptr)
            return false;
    }
    else
    {
        if (__begin_ < __first_)
            return false;
        if (__end_ < __begin_)
            return false;
        if (__end_cap() < __end_)
            return false;
    }
    return true;
}

//  Default constructs __n objects starting at __end_
//  throws if construction throws
//  Precondition:  __n > 0
//  Precondition:  size() + __n <= capacity()
//  Postcondition:  size() == size() + __n
template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::__construct_at_end(size_type __n)
{
    _ConstructTransaction __tx(&this->__end_, __n);
    for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
        __alloc_traits::construct(this->__alloc(), _VSTD::__to_address(__tx.__pos_));
    }
}

//  Copy constructs __n objects starting at __end_ from __x
//  throws if construction throws
//  Precondition:  __n > 0
//  Precondition:  size() + __n <= capacity()
//  Postcondition:  size() == old size() + __n
//  Postcondition:  [i] == __x for all i in [size() - __n, __n)
template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::__construct_at_end(size_type __n, const_reference __x)
{
    _ConstructTransaction __tx(&this->__end_, __n);
    for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
        __alloc_traits::construct(this->__alloc(),
            _VSTD::__to_address(__tx.__pos_), __x);
    }
}

template <class _Tp, class _Allocator>
template <class _InputIter>
_LIBCPP_CONSTEXPR_SINCE_CXX20 __enable_if_t<__is_exactly_cpp17_input_iterator<_InputIter>::value>
__split_buffer<_Tp, _Allocator>::__construct_at_end(_InputIter __first, _InputIter __last)
{
  __construct_at_end_with_sentinel(__first, __last);
}

template <class _Tp, class _Allocator>
template <class _Iterator, class _Sentinel>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void __split_buffer<_Tp, _Allocator>::__construct_at_end_with_sentinel(_Iterator __first, _Sentinel __last) {
    __alloc_rr& __a = this->__alloc();
    for (; __first != __last; ++__first)
    {
        if (__end_ == __end_cap())
        {
            size_type __old_cap = __end_cap() - __first_;
            size_type __new_cap = _VSTD::max<size_type>(2 * __old_cap, 8);
            __split_buffer __buf(__new_cap, 0, __a);
            for (pointer __p = __begin_; __p != __end_; ++__p, (void) ++__buf.__end_)
                __alloc_traits::construct(__buf.__alloc(),
                        _VSTD::__to_address(__buf.__end_), _VSTD::move(*__p));
            swap(__buf);
        }
        __alloc_traits::construct(__a, _VSTD::__to_address(this->__end_), *__first);
        ++this->__end_;
    }
}
template <class _Tp, class _Allocator>
template <class _ForwardIterator>
_LIBCPP_CONSTEXPR_SINCE_CXX20 __enable_if_t<__is_cpp17_forward_iterator<_ForwardIterator>::value>
__split_buffer<_Tp, _Allocator>::__construct_at_end(_ForwardIterator __first, _ForwardIterator __last)
{
  __construct_at_end_with_size(__first, std::distance(__first, __last));
}

template <class _Tp, class _Allocator>
template <class _ForwardIterator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void __split_buffer<_Tp, _Allocator>::__construct_at_end_with_size(_ForwardIterator __first, size_type __n) {
    _ConstructTransaction __tx(&this->__end_, __n);
    for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_, (void) ++__first) {
        __alloc_traits::construct(this->__alloc(),
            _VSTD::__to_address(__tx.__pos_), *__first);
    }
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
inline
void
__split_buffer<_Tp, _Allocator>::__destruct_at_begin(pointer __new_begin, false_type)
{
    while (__begin_ != __new_begin)
        __alloc_traits::destroy(__alloc(), _VSTD::__to_address(__begin_++));
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
inline
void
__split_buffer<_Tp, _Allocator>::__destruct_at_begin(pointer __new_begin, true_type)
{
    __begin_ = __new_begin;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
inline _LIBCPP_HIDE_FROM_ABI
void
__split_buffer<_Tp, _Allocator>::__destruct_at_end(pointer __new_last, false_type) _NOEXCEPT
{
    while (__new_last != __end_)
        __alloc_traits::destroy(__alloc(), _VSTD::__to_address(--__end_));
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
inline _LIBCPP_HIDE_FROM_ABI
void
__split_buffer<_Tp, _Allocator>::__destruct_at_end(pointer __new_last, true_type) _NOEXCEPT
{
    __end_ = __new_last;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
__split_buffer<_Tp, _Allocator>::__split_buffer(size_type __cap, size_type __start, __alloc_rr& __a)
    : __end_cap_(nullptr, __a)
{
    if (__cap == 0) {
        __first_ = nullptr;
    } else {
        auto __allocation = std::__allocate_at_least(__alloc(), __cap);
        __first_ = __allocation.ptr;
        __cap = __allocation.count;
    }
    __begin_ = __end_ = __first_ + __start;
    __end_cap() = __first_ + __cap;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
__split_buffer<_Tp, _Allocator>::~__split_buffer()
{
    clear();
    if (__first_)
        __alloc_traits::deallocate(__alloc(), __first_, capacity());
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
__split_buffer<_Tp, _Allocator>::__split_buffer(__split_buffer&& __c)
    _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value)
    : __first_(_VSTD::move(__c.__first_)),
      __begin_(_VSTD::move(__c.__begin_)),
      __end_(_VSTD::move(__c.__end_)),
      __end_cap_(_VSTD::move(__c.__end_cap_))
{
    __c.__first_ = nullptr;
    __c.__begin_ = nullptr;
    __c.__end_ = nullptr;
    __c.__end_cap() = nullptr;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
__split_buffer<_Tp, _Allocator>::__split_buffer(__split_buffer&& __c, const __alloc_rr& __a)
    : __end_cap_(nullptr, __a)
{
    if (__a == __c.__alloc())
    {
        __first_ = __c.__first_;
        __begin_ = __c.__begin_;
        __end_ = __c.__end_;
        __end_cap() = __c.__end_cap();
        __c.__first_ = nullptr;
        __c.__begin_ = nullptr;
        __c.__end_ = nullptr;
        __c.__end_cap() = nullptr;
    }
    else
    {
        auto __allocation = std::__allocate_at_least(__alloc(), __c.size());
        __first_ = __allocation.ptr;
        __begin_ = __end_ = __first_;
        __end_cap() = __first_ + __allocation.count;
        typedef move_iterator<iterator> _Ip;
        __construct_at_end(_Ip(__c.begin()), _Ip(__c.end()));
    }
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
__split_buffer<_Tp, _Allocator>&
__split_buffer<_Tp, _Allocator>::operator=(__split_buffer&& __c)
    _NOEXCEPT_((__alloc_traits::propagate_on_container_move_assignment::value &&
                is_nothrow_move_assignable<allocator_type>::value) ||
               !__alloc_traits::propagate_on_container_move_assignment::value)
{
    clear();
    shrink_to_fit();
    __first_ = __c.__first_;
    __begin_ = __c.__begin_;
    __end_ = __c.__end_;
    __end_cap() = __c.__end_cap();
    __move_assign_alloc(__c,
        integral_constant<bool,
                          __alloc_traits::propagate_on_container_move_assignment::value>());
    __c.__first_ = __c.__begin_ = __c.__end_ = __c.__end_cap() = nullptr;
    return *this;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::swap(__split_buffer& __x)
        _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value||
                   __is_nothrow_swappable<__alloc_rr>::value)
{
    _VSTD::swap(__first_, __x.__first_);
    _VSTD::swap(__begin_, __x.__begin_);
    _VSTD::swap(__end_, __x.__end_);
    _VSTD::swap(__end_cap(), __x.__end_cap());
    _VSTD::__swap_allocator(__alloc(), __x.__alloc());
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::reserve(size_type __n)
{
    if (__n < capacity())
    {
        __split_buffer<value_type, __alloc_rr&> __t(__n, 0, __alloc());
        __t.__construct_at_end(move_iterator<pointer>(__begin_),
                               move_iterator<pointer>(__end_));
        _VSTD::swap(__first_, __t.__first_);
        _VSTD::swap(__begin_, __t.__begin_);
        _VSTD::swap(__end_, __t.__end_);
        _VSTD::swap(__end_cap(), __t.__end_cap());
    }
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::shrink_to_fit() _NOEXCEPT
{
    if (capacity() > size())
    {
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
        try
        {
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
            __split_buffer<value_type, __alloc_rr&> __t(size(), 0, __alloc());
            __t.__construct_at_end(move_iterator<pointer>(__begin_),
                                   move_iterator<pointer>(__end_));
            __t.__end_ = __t.__begin_ + (__end_ - __begin_);
            _VSTD::swap(__first_, __t.__first_);
            _VSTD::swap(__begin_, __t.__begin_);
            _VSTD::swap(__end_, __t.__end_);
            _VSTD::swap(__end_cap(), __t.__end_cap());
#ifndef _LIBCPP_HAS_NO_EXCEPTIONS
        }
        catch (...)
        {
        }
#endif // _LIBCPP_HAS_NO_EXCEPTIONS
    }
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::push_front(const_reference __x)
{
    if (__begin_ == __first_)
    {
        if (__end_ < __end_cap())
        {
            difference_type __d = __end_cap() - __end_;
            __d = (__d + 1) / 2;
            __begin_ = _VSTD::move_backward(__begin_, __end_, __end_ + __d);
            __end_ += __d;
        }
        else
        {
            size_type __c = std::max<size_type>(2 * static_cast<size_t>(__end_cap() - __first_), 1);
            __split_buffer<value_type, __alloc_rr&> __t(__c, (__c + 3) / 4, __alloc());
            __t.__construct_at_end(move_iterator<pointer>(__begin_),
                                   move_iterator<pointer>(__end_));
            _VSTD::swap(__first_, __t.__first_);
            _VSTD::swap(__begin_, __t.__begin_);
            _VSTD::swap(__end_, __t.__end_);
            _VSTD::swap(__end_cap(), __t.__end_cap());
        }
    }
    __alloc_traits::construct(__alloc(), _VSTD::__to_address(__begin_-1), __x);
    --__begin_;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::push_front(value_type&& __x)
{
    if (__begin_ == __first_)
    {
        if (__end_ < __end_cap())
        {
            difference_type __d = __end_cap() - __end_;
            __d = (__d + 1) / 2;
            __begin_ = _VSTD::move_backward(__begin_, __end_, __end_ + __d);
            __end_ += __d;
        }
        else
        {
            size_type __c = std::max<size_type>(2 * static_cast<size_t>(__end_cap() - __first_), 1);
            __split_buffer<value_type, __alloc_rr&> __t(__c, (__c + 3) / 4, __alloc());
            __t.__construct_at_end(move_iterator<pointer>(__begin_),
                                   move_iterator<pointer>(__end_));
            _VSTD::swap(__first_, __t.__first_);
            _VSTD::swap(__begin_, __t.__begin_);
            _VSTD::swap(__end_, __t.__end_);
            _VSTD::swap(__end_cap(), __t.__end_cap());
        }
    }
    __alloc_traits::construct(__alloc(), _VSTD::__to_address(__begin_-1),
            _VSTD::move(__x));
    --__begin_;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
inline _LIBCPP_HIDE_FROM_ABI
void
__split_buffer<_Tp, _Allocator>::push_back(const_reference __x)
{
    if (__end_ == __end_cap())
    {
        if (__begin_ > __first_)
        {
            difference_type __d = __begin_ - __first_;
            __d = (__d + 1) / 2;
            __end_ = _VSTD::move(__begin_, __end_, __begin_ - __d);
            __begin_ -= __d;
        }
        else
        {
            size_type __c = std::max<size_type>(2 * static_cast<size_t>(__end_cap() - __first_), 1);
            __split_buffer<value_type, __alloc_rr&> __t(__c, __c / 4, __alloc());
            __t.__construct_at_end(move_iterator<pointer>(__begin_),
                                   move_iterator<pointer>(__end_));
            _VSTD::swap(__first_, __t.__first_);
            _VSTD::swap(__begin_, __t.__begin_);
            _VSTD::swap(__end_, __t.__end_);
            _VSTD::swap(__end_cap(), __t.__end_cap());
        }
    }
    __alloc_traits::construct(__alloc(), _VSTD::__to_address(__end_), __x);
    ++__end_;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::push_back(value_type&& __x)
{
    if (__end_ == __end_cap())
    {
        if (__begin_ > __first_)
        {
            difference_type __d = __begin_ - __first_;
            __d = (__d + 1) / 2;
            __end_ = _VSTD::move(__begin_, __end_, __begin_ - __d);
            __begin_ -= __d;
        }
        else
        {
            size_type __c = std::max<size_type>(2 * static_cast<size_t>(__end_cap() - __first_), 1);
            __split_buffer<value_type, __alloc_rr&> __t(__c, __c / 4, __alloc());
            __t.__construct_at_end(move_iterator<pointer>(__begin_),
                                   move_iterator<pointer>(__end_));
            _VSTD::swap(__first_, __t.__first_);
            _VSTD::swap(__begin_, __t.__begin_);
            _VSTD::swap(__end_, __t.__end_);
            _VSTD::swap(__end_cap(), __t.__end_cap());
        }
    }
    __alloc_traits::construct(__alloc(), _VSTD::__to_address(__end_),
            _VSTD::move(__x));
    ++__end_;
}

template <class _Tp, class _Allocator>
template <class... _Args>
_LIBCPP_CONSTEXPR_SINCE_CXX20
void
__split_buffer<_Tp, _Allocator>::emplace_back(_Args&&... __args)
{
    if (__end_ == __end_cap())
    {
        if (__begin_ > __first_)
        {
            difference_type __d = __begin_ - __first_;
            __d = (__d + 1) / 2;
            __end_ = _VSTD::move(__begin_, __end_, __begin_ - __d);
            __begin_ -= __d;
        }
        else
        {
            size_type __c = std::max<size_type>(2 * static_cast<size_t>(__end_cap() - __first_), 1);
            __split_buffer<value_type, __alloc_rr&> __t(__c, __c / 4, __alloc());
            __t.__construct_at_end(move_iterator<pointer>(__begin_),
                                   move_iterator<pointer>(__end_));
            _VSTD::swap(__first_, __t.__first_);
            _VSTD::swap(__begin_, __t.__begin_);
            _VSTD::swap(__end_, __t.__end_);
            _VSTD::swap(__end_cap(), __t.__end_cap());
        }
    }
    __alloc_traits::construct(__alloc(), _VSTD::__to_address(__end_),
                              _VSTD::forward<_Args>(__args)...);
    ++__end_;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
inline _LIBCPP_HIDE_FROM_ABI
void
swap(__split_buffer<_Tp, _Allocator>& __x, __split_buffer<_Tp, _Allocator>& __y)
        _NOEXCEPT_(_NOEXCEPT_(__x.swap(__y)))
{
    __x.swap(__y);
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___SPLIT_BUFFER