xref: /freebsd/contrib/llvm-project/libcxx/include/__split_buffer (revision 700637cbb5e582861067a11aaca4d053546871d2)

// -*- 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/conditional.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/integral_constant.h>
#include <__type_traits/is_nothrow_assignable.h>
#include <__type_traits/is_nothrow_constructible.h>
#include <__type_traits/is_replaceable.h>
#include <__type_traits/is_swappable.h>
#include <__type_traits/is_trivially_destructible.h>
#include <__type_traits/is_trivially_relocatable.h>
#include <__type_traits/remove_reference.h>
#include <__utility/forward.h>
#include <__utility/move.h>

#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_, __cap_). 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_NODEBUG     = __libcpp_remove_reference_t<allocator_type>;
  using __alloc_traits _LIBCPP_NODEBUG = 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;

  // A __split_buffer contains the following members which may be trivially relocatable:
  // - pointer: may be trivially relocatable, so it's checked
  // - allocator_type: may be trivially relocatable, so it's checked
  // __split_buffer doesn't have any self-references, so it's trivially relocatable if its members are.
  using __trivially_relocatable _LIBCPP_NODEBUG = __conditional_t<
      __libcpp_is_trivially_relocatable<pointer>::value && __libcpp_is_trivially_relocatable<allocator_type>::value,
      __split_buffer,
      void>;
  using __replaceable _LIBCPP_NODEBUG =
      __conditional_t<__is_replaceable_v<pointer> && __container_allocator_is_replaceable<__alloc_traits>::value,
                      __split_buffer,
                      void>;

  pointer __first_;
  pointer __begin_;
  pointer __end_;
  _LIBCPP_COMPRESSED_PAIR(pointer, __cap_, allocator_type, __alloc_);

  __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), __cap_(nullptr) {}

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

  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit __split_buffer(const __alloc_rr& __a)
      : __first_(nullptr), __begin_(nullptr), __end_(nullptr), __cap_(nullptr), __alloc_(__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 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>(__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>(__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 shrink_to_fit() _NOEXCEPT;

  template <class... _Args>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void emplace_front(_Args&&... __args);
  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 _ForwardIterator, __enable_if_t<__has_forward_iterator_category<_ForwardIterator>::value, int> = 0>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
  __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_v<__alloc_rr>);

  _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_ = std::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 (__cap_ != nullptr)
      return false;
  } else {
    if (__begin_ < __first_)
      return false;
    if (__end_ < __begin_)
      return false;
    if (__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(std::addressof(this->__end_), __n);
  for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
    __alloc_traits::construct(__alloc_, std::__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(std::addressof(this->__end_), __n);
  for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
    __alloc_traits::construct(__alloc_, std::__to_address(__tx.__pos_), __x);
  }
}

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 = __alloc_;
  for (; __first != __last; ++__first) {
    if (__end_ == __cap_) {
      size_type __old_cap = __cap_ - __first_;
      size_type __new_cap = std::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_, std::__to_address(__buf.__end_), std::move(*__p));
      swap(__buf);
    }
    __alloc_traits::construct(__a, std::__to_address(this->__end_), *__first);
    ++this->__end_;
  }
}
template <class _Tp, class _Allocator>
template <class _ForwardIterator, __enable_if_t<__has_forward_iterator_category<_ForwardIterator>::value, int> >
_LIBCPP_CONSTEXPR_SINCE_CXX20 void
__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(std::addressof(this->__end_), __n);
  for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_, (void)++__first) {
    __alloc_traits::construct(__alloc_, std::__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_, std::__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_, std::__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)
    : __cap_(nullptr), __alloc_(__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;
  __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_(std::move(__c.__first_)),
      __begin_(std::move(__c.__begin_)),
      __end_(std::move(__c.__end_)),
      __cap_(std::move(__c.__cap_)),
      __alloc_(std::move(__c.__alloc_)) {
  __c.__first_ = nullptr;
  __c.__begin_ = nullptr;
  __c.__end_   = nullptr;
  __c.__cap_   = nullptr;
}

template <class _Tp, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20
__split_buffer<_Tp, _Allocator>::__split_buffer(__split_buffer&& __c, const __alloc_rr& __a)
    : __cap_(nullptr), __alloc_(__a) {
  if (__a == __c.__alloc_) {
    __first_     = __c.__first_;
    __begin_     = __c.__begin_;
    __end_       = __c.__end_;
    __cap_       = __c.__cap_;
    __c.__first_ = nullptr;
    __c.__begin_ = nullptr;
    __c.__end_   = nullptr;
    __c.__cap_   = nullptr;
  } else {
    auto __allocation = std::__allocate_at_least(__alloc_, __c.size());
    __first_          = __allocation.ptr;
    __begin_ = __end_ = __first_;
    __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_;
  __cap_   = __c.__cap_;
  __move_assign_alloc(__c, integral_constant<bool, __alloc_traits::propagate_on_container_move_assignment::value>());
  __c.__first_ = __c.__begin_ = __c.__end_ = __c.__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_v<__alloc_rr>) {
  std::swap(__first_, __x.__first_);
  std::swap(__begin_, __x.__begin_);
  std::swap(__end_, __x.__end_);
  std::swap(__cap_, __x.__cap_);
  std::__swap_allocator(__alloc_, __x.__alloc_);
}

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

template <class _Tp, class _Allocator>
template <class... _Args>
_LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator>::emplace_front(_Args&&... __args) {
  if (__begin_ == __first_) {
    if (__end_ < __cap_) {
      difference_type __d = __cap_ - __end_;
      __d                 = (__d + 1) / 2;
      __begin_            = std::move_backward(__begin_, __end_, __end_ + __d);
      __end_ += __d;
    } else {
      size_type __c = std::max<size_type>(2 * static_cast<size_type>(__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_));
      std::swap(__first_, __t.__first_);
      std::swap(__begin_, __t.__begin_);
      std::swap(__end_, __t.__end_);
      std::swap(__cap_, __t.__cap_);
    }
  }
  __alloc_traits::construct(__alloc_, std::__to_address(__begin_ - 1), std::forward<_Args>(__args)...);
  --__begin_;
}

template <class _Tp, class _Allocator>
template <class... _Args>
_LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator>::emplace_back(_Args&&... __args) {
  if (__end_ == __cap_) {
    if (__begin_ > __first_) {
      difference_type __d = __begin_ - __first_;
      __d                 = (__d + 1) / 2;
      __end_              = std::move(__begin_, __end_, __begin_ - __d);
      __begin_ -= __d;
    } else {
      size_type __c = std::max<size_type>(2 * static_cast<size_type>(__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_));
      std::swap(__first_, __t.__first_);
      std::swap(__begin_, __t.__begin_);
      std::swap(__end_, __t.__end_);
      std::swap(__cap_, __t.__cap_);
    }
  }
  __alloc_traits::construct(__alloc_, std::__to_address(__end_), std::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