libcxx/include/__bit_reference

// -*- 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___BIT_REFERENCE
#define _LIBCPP___BIT_REFERENCE

#include <__algorithm/comp.h>
#include <__algorithm/copy.h>
#include <__algorithm/copy_backward.h>
#include <__algorithm/copy_n.h>
#include <__algorithm/equal.h>
#include <__algorithm/fill_n.h>
#include <__algorithm/in_out_result.h>
#include <__algorithm/min.h>
#include <__algorithm/rotate.h>
#include <__algorithm/specialized_algorithms.h>
#include <__assert>
#include <__bit/countr.h>
#include <__compare/ordering.h>
#include <__config>
#include <__cstddef/ptrdiff_t.h>
#include <__cstddef/size_t.h>
#include <__functional/identity.h>
#include <__fwd/bit_reference.h>
#include <__iterator/iterator_traits.h>
#include <__memory/construct_at.h>
#include <__memory/pointer_traits.h>
#include <__type_traits/conditional.h>
#include <__type_traits/desugars_to.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/is_constant_evaluated.h>
#include <__type_traits/is_unsigned.h>
#include <__type_traits/void_t.h>
#include <__utility/pair.h>
#include <__utility/swap.h>
#include <climits>

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

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Cp>
class __bit_const_reference;

template <class _Tp>
struct __has_storage_type {
  static const bool value = false;
};

template <class, class>
struct __size_difference_type_traits {
  using difference_type = ptrdiff_t;
  using size_type       = size_t;
};

template <class _Cp>
struct __size_difference_type_traits<_Cp, __void_t<typename _Cp::difference_type, typename _Cp::size_type> > {
  using difference_type = typename _Cp::difference_type;
  using size_type       = typename _Cp::size_type;
};

// The `__x_mask` functions are designed to work exclusively with any unsigned `_StorageType`s, including small
// integral types such as unsigned char/short, `uint8_t`, and `uint16_t`. To prevent undefined behavior or
// ambiguities due to integral promotions for the small integral types, all intermediate bitwise operations are
// explicitly cast back to the unsigned `_StorageType`.

// Creates a mask of type `_StorageType` with a specified number of leading zeros (__clz) and sets all remaining
// bits to one.
template <class _StorageType>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _StorageType __trailing_mask(unsigned __clz) {
  static_assert(is_unsigned<_StorageType>::value, "__trailing_mask only works with unsigned types");
  return static_cast<_StorageType>(~static_cast<_StorageType>(0)) >> __clz;
}

// Creates a mask of type `_StorageType` with a specified number of trailing zeros (__ctz) and sets all remaining
// bits to one.
template <class _StorageType>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _StorageType __leading_mask(unsigned __ctz) {
  static_assert(is_unsigned<_StorageType>::value, "__leading_mask only works with unsigned types");
  return static_cast<_StorageType>(~static_cast<_StorageType>(0)) << __ctz;
}

// Creates a mask of type `_StorageType` with a specified number of leading zeros (__clz), a specified number of
// trailing zeros (__ctz), and sets all bits in between to one.
template <class _StorageType>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _StorageType __middle_mask(unsigned __clz, unsigned __ctz) {
  static_assert(is_unsigned<_StorageType>::value, "__middle_mask only works with unsigned types");
  return std::__leading_mask<_StorageType>(__ctz) & std::__trailing_mask<_StorageType>(__clz);
}

// This function is designed to operate correctly even for smaller integral types like `uint8_t`, `uint16_t`,
// or `unsigned short`.
// See https://github.com/llvm/llvm-project/pull/122410.
template <class _StoragePointer>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
__fill_masked_range(_StoragePointer __word, unsigned __clz, unsigned __ctz, bool __fill_val) {
  static_assert(is_unsigned<typename pointer_traits<_StoragePointer>::element_type>::value,
                "__fill_masked_range must be called with unsigned type");
  using _StorageType = typename pointer_traits<_StoragePointer>::element_type;
  _LIBCPP_ASSERT_VALID_INPUT_RANGE(
      __ctz + __clz < sizeof(_StorageType) * CHAR_BIT, "__fill_masked_range called with invalid range");
  _StorageType __m = std::__middle_mask<_StorageType>(__clz, __ctz);
  if (__fill_val)
    *__word |= __m;
  else
    *__word &= ~__m;
}

template <class _Cp, bool = __has_storage_type<_Cp>::value>
class __bit_reference {
  using __storage_type _LIBCPP_NODEBUG    = typename _Cp::__storage_type;
  using __storage_pointer _LIBCPP_NODEBUG = typename _Cp::__storage_pointer;

  __storage_pointer __seg_;
  __storage_type __mask_;

  friend typename _Cp::__self;

  friend class __bit_const_reference<_Cp>;
  friend class __bit_iterator<_Cp, false>;

public:
  using __container _LIBCPP_NODEBUG = typename _Cp::__self;

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_reference(const __bit_reference&) = default;

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 operator bool() const _NOEXCEPT {
    return static_cast<bool>(*__seg_ & __mask_);
  }
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool operator~() const _NOEXCEPT {
    return !static_cast<bool>(*this);
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_reference& operator=(bool __x) _NOEXCEPT {
    if (__x)
      *__seg_ |= __mask_;
    else
      *__seg_ &= ~__mask_;
    return *this;
  }

#if _LIBCPP_STD_VER >= 23
  _LIBCPP_HIDE_FROM_ABI constexpr const __bit_reference& operator=(bool __x) const noexcept {
    if (__x)
      *__seg_ |= __mask_;
    else
      *__seg_ &= ~__mask_;
    return *this;
  }
#endif

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_reference& operator=(const __bit_reference& __x) _NOEXCEPT {
    return operator=(static_cast<bool>(__x));
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void flip() _NOEXCEPT { *__seg_ ^= __mask_; }

private:
  _LIBCPP_HIDE_FROM_ABI
  _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit __bit_reference(__storage_pointer __s, __storage_type __m) _NOEXCEPT
      : __seg_(__s),
        __mask_(__m) {}
};

template <class _Cp>
class __bit_reference<_Cp, false> {};

template <class _Cp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
swap(__bit_reference<_Cp> __x, __bit_reference<_Cp> __y) _NOEXCEPT {
  bool __t = __x;
  __x      = __y;
  __y      = __t;
}

template <class _Cp, class _Dp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
swap(__bit_reference<_Cp> __x, __bit_reference<_Dp> __y) _NOEXCEPT {
  bool __t = __x;
  __x      = __y;
  __y      = __t;
}

template <class _Cp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void swap(__bit_reference<_Cp> __x, bool& __y) _NOEXCEPT {
  bool __t = __x;
  __x      = __y;
  __y      = __t;
}

template <class _Cp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void swap(bool& __x, __bit_reference<_Cp> __y) _NOEXCEPT {
  bool __t = __x;
  __x      = __y;
  __y      = __t;
}

template <class _Cp>
class __bit_const_reference {
  using __storage_type _LIBCPP_NODEBUG    = typename _Cp::__storage_type;
  using __storage_pointer _LIBCPP_NODEBUG = typename _Cp::__const_storage_pointer;

  __storage_pointer __seg_;
  __storage_type __mask_;

  friend typename _Cp::__self;
  friend class __bit_iterator<_Cp, true>;

public:
  using __container _LIBCPP_NODEBUG = typename _Cp::__self;

  _LIBCPP_HIDE_FROM_ABI __bit_const_reference(const __bit_const_reference&) = default;
  __bit_const_reference& operator=(const __bit_const_reference&)            = delete;

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_const_reference(const __bit_reference<_Cp>& __x) _NOEXCEPT
      : __seg_(__x.__seg_),
        __mask_(__x.__mask_) {}

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR operator bool() const _NOEXCEPT {
    return static_cast<bool>(*__seg_ & __mask_);
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator<_Cp, true> operator&() const _NOEXCEPT {
    return __bit_iterator<_Cp, true>(__seg_, static_cast<unsigned>(std::__countr_zero(__mask_)));
  }

private:
  _LIBCPP_HIDE_FROM_ABI
  _LIBCPP_CONSTEXPR explicit __bit_const_reference(__storage_pointer __s, __storage_type __m) _NOEXCEPT
      : __seg_(__s),
        __mask_(__m) {}
};

template <class _Cp>
struct __bit_array {
  using difference_type _LIBCPP_NODEBUG   = typename __size_difference_type_traits<_Cp>::difference_type;
  using __storage_type _LIBCPP_NODEBUG    = typename _Cp::__storage_type;
  using __storage_pointer _LIBCPP_NODEBUG = typename _Cp::__storage_pointer;
  using iterator _LIBCPP_NODEBUG          = typename _Cp::iterator;

  static const unsigned __bits_per_word = _Cp::__bits_per_word;
  static const unsigned _Np             = 4;

  difference_type __size_;
  __storage_type __word_[_Np];

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static difference_type capacity() {
    return static_cast<difference_type>(_Np * __bits_per_word);
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit __bit_array(difference_type __s) : __size_(__s) {
    if (__libcpp_is_constant_evaluated()) {
      for (size_t __i = 0; __i != __bit_array<_Cp>::_Np; ++__i)
        std::__construct_at(__word_ + __i, 0);
    }
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 iterator begin() {
    return iterator(pointer_traits<__storage_pointer>::pointer_to(__word_[0]), 0);
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 iterator end() {
    return iterator(pointer_traits<__storage_pointer>::pointer_to(__word_[0]) + __size_ / __bits_per_word,
                    static_cast<unsigned>(__size_ % __bits_per_word));
  }
};

template <class _Cp, bool _IsConst, typename _Cp::__storage_type>
class _LIBCPP_WARN_UNUSED __bit_iterator {
public:
  using difference_type = typename __size_difference_type_traits<_Cp>::difference_type;
  using value_type      = bool;
  using pointer         = __bit_iterator;
#ifndef _LIBCPP_ABI_BITSET_VECTOR_BOOL_CONST_SUBSCRIPT_RETURN_BOOL
  using reference = __conditional_t<_IsConst, __bit_const_reference<_Cp>, __bit_reference<_Cp> >;
#else
  using reference = __conditional_t<_IsConst, bool, __bit_reference<_Cp> >;
#endif
  using iterator_category = random_access_iterator_tag;

private:
  using __storage_type _LIBCPP_NODEBUG = typename _Cp::__storage_type;
  using __storage_pointer _LIBCPP_NODEBUG =
      __conditional_t<_IsConst, typename _Cp::__const_storage_pointer, typename _Cp::__storage_pointer>;

  static const unsigned __bits_per_word = _Cp::__bits_per_word;

  __storage_pointer __seg_;
  unsigned __ctz_;

public:
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator() _NOEXCEPT
#if _LIBCPP_STD_VER >= 14
      : __seg_(nullptr),
        __ctz_(0)
#endif
  {
  }

#ifdef _LIBCPP_ABI_TRIVIALLY_COPYABLE_BIT_ITERATOR
  template <bool _IsConstDep = _IsConst, __enable_if_t<_IsConstDep, int> = 0>
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator(const __bit_iterator<_Cp, false>& __it) _NOEXCEPT
      : __seg_(__it.__seg_),
        __ctz_(__it.__ctz_) {}

  _LIBCPP_HIDE_FROM_ABI __bit_iterator(const __bit_iterator&)            = default;
  _LIBCPP_HIDE_FROM_ABI __bit_iterator& operator=(const __bit_iterator&) = default;
#else
  // When _IsConst=false, this is the copy constructor.
  // It is non-trivial. Making it trivial would break ABI.
  // When _IsConst=true, this is a converting constructor;
  // the copy and move constructors are implicitly generated
  // and trivial.
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator(const __bit_iterator<_Cp, false>& __it) _NOEXCEPT
      : __seg_(__it.__seg_),
        __ctz_(__it.__ctz_) {}

  // When _IsConst=false, we have a user-provided copy constructor,
  // so we must also provide a copy assignment operator because
  // the implicit generation of a defaulted one is deprecated.
  // When _IsConst=true, the assignment operators are
  // implicitly generated and trivial.
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator&
  operator=(const _If<_IsConst, struct __private_nat, __bit_iterator>& __it) {
    __seg_ = __it.__seg_;
    __ctz_ = __it.__ctz_;
    return *this;
  }
#endif

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference operator*() const _NOEXCEPT {
    _LIBCPP_ASSERT_INTERNAL(__ctz_ < __bits_per_word, "Dereferencing an invalid __bit_iterator.");
    return __conditional_t<_IsConst, __bit_const_reference<_Cp>, __bit_reference<_Cp> >(
        __seg_, __storage_type(1) << __ctz_);
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator& operator++() {
    if (__ctz_ != __bits_per_word - 1)
      ++__ctz_;
    else {
      __ctz_ = 0;
      ++__seg_;
    }
    return *this;
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator operator++(int) {
    __bit_iterator __tmp = *this;
    ++(*this);
    return __tmp;
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator& operator--() {
    if (__ctz_ != 0)
      --__ctz_;
    else {
      __ctz_ = __bits_per_word - 1;
      --__seg_;
    }
    return *this;
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator operator--(int) {
    __bit_iterator __tmp = *this;
    --(*this);
    return __tmp;
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator& operator+=(difference_type __n) {
    if (__n >= 0)
      __seg_ += (__n + __ctz_) / __bits_per_word;
    else
      __seg_ += static_cast<difference_type>(__n - __bits_per_word + __ctz_ + 1) /
                static_cast<difference_type>(__bits_per_word);
    __n &= (__bits_per_word - 1);
    __ctz_ = static_cast<unsigned>((__n + __ctz_) % __bits_per_word);
    return *this;
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator& operator-=(difference_type __n) {
    return *this += -__n;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator
  operator+(difference_type __n) const {
    __bit_iterator __t(*this);
    __t += __n;
    return __t;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator
  operator-(difference_type __n) const {
    __bit_iterator __t(*this);
    __t -= __n;
    return __t;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend __bit_iterator
  operator+(difference_type __n, const __bit_iterator& __it) {
    return __it + __n;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend difference_type
  operator-(const __bit_iterator& __x, const __bit_iterator& __y) {
    return (__x.__seg_ - __y.__seg_) * __bits_per_word + __x.__ctz_ - __y.__ctz_;
  }

  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference
  operator[](difference_type __n) const {
    return *(*this + __n);
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
  operator==(const __bit_iterator& __x, const __bit_iterator& __y) {
    return __x.__seg_ == __y.__seg_ && __x.__ctz_ == __y.__ctz_;
  }

#if _LIBCPP_STD_VER <= 17
  _LIBCPP_HIDE_FROM_ABI
  _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool operator!=(const __bit_iterator& __x, const __bit_iterator& __y) {
    return !(__x == __y);
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
  operator<(const __bit_iterator& __x, const __bit_iterator& __y) {
    return __x.__seg_ < __y.__seg_ || (__x.__seg_ == __y.__seg_ && __x.__ctz_ < __y.__ctz_);
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
  operator>(const __bit_iterator& __x, const __bit_iterator& __y) {
    return __y < __x;
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
  operator<=(const __bit_iterator& __x, const __bit_iterator& __y) {
    return !(__y < __x);
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
  operator>=(const __bit_iterator& __x, const __bit_iterator& __y) {
    return !(__x < __y);
  }
#else  // _LIBCPP_STD_VER <= 17
  _LIBCPP_HIDE_FROM_ABI constexpr friend strong_ordering
  operator<=>(const __bit_iterator& __x, const __bit_iterator& __y) {
    if (__x.__seg_ < __y.__seg_)
      return strong_ordering::less;

    if (__x.__seg_ == __y.__seg_)
      return __x.__ctz_ <=> __y.__ctz_;

    return strong_ordering::greater;
  }
#endif // _LIBCPP_STD_VER <= 17

private:
  _LIBCPP_HIDE_FROM_ABI
  _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit __bit_iterator(__storage_pointer __s, unsigned __ctz) _NOEXCEPT
      : __seg_(__s),
        __ctz_(__ctz) {
    _LIBCPP_ASSERT_INTERNAL(
        __ctz_ < __bits_per_word, "__bit_iterator initialized with an invalid number of trailing zeros.");
  }

  friend typename _Cp::__self;

  friend class __bit_reference<_Cp>;
  friend class __bit_const_reference<_Cp>;
  friend class __bit_iterator<_Cp, true>;
  template <class _Dp>
  friend struct __bit_array;

  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 friend __bit_iterator<_Dp, false> __copy_backward_aligned(
      __bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 friend __bit_iterator<_Dp, false> __copy_backward_unaligned(
      __bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _AlgPolicy>
  friend struct __copy_backward_impl;
  template <class, class _Dp>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 friend pair<__bit_iterator<_Dp, false>, __bit_iterator<_Dp, false> >
      __rotate(__bit_iterator<_Dp, false>, __bit_iterator<_Dp, false>, __bit_iterator<_Dp, false>);
  template <class _Dp, bool _IsConst1, bool _IsConst2>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
      __equal_aligned(__bit_iterator<_Dp, _IsConst1>, __bit_iterator<_Dp, _IsConst1>, __bit_iterator<_Dp, _IsConst2>);
  template <class _Dp, bool _IsConst1, bool _IsConst2>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
      __equal_unaligned(__bit_iterator<_Dp, _IsConst1>, __bit_iterator<_Dp, _IsConst1>, __bit_iterator<_Dp, _IsConst2>);
  template <class _Dp,
            bool _IsConst1,
            bool _IsConst2,
            class _BinaryPredicate,
            class _Proj1,
            class _Proj2,
            __enable_if_t<__is_identity<_Proj1>::value && __is_identity<_Proj2>::value &&
                              __desugars_to_v<__equal_tag, _BinaryPredicate, bool, bool>,
                          int> >
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool __equal_iter_impl(
      __bit_iterator<_Dp, _IsConst1>,
      __bit_iterator<_Dp, _IsConst1>,
      __bit_iterator<_Dp, _IsConst2>,
      _BinaryPredicate,
      _Proj1&,
      _Proj2&);
  template <bool,
            class _Dp,
            bool _IsConst1,
            bool _IsConst2,
            class _Pred,
            class _Proj1,
            class _Proj2,
            __enable_if_t<__desugars_to_v<__equal_tag, _Pred, bool, bool> && __is_identity<_Proj1>::value &&
                              __is_identity<_Proj2>::value,
                          int> >
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool __equal_impl(
      __bit_iterator<_Dp, _IsConst1> __first1,
      __bit_iterator<_Dp, _IsConst1> __last1,
      __bit_iterator<_Dp, _IsConst2> __first2,
      __bit_iterator<_Dp, _IsConst2>,
      _Pred&,
      _Proj1&,
      _Proj2&);
  template <bool _ToFind, class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 friend __bit_iterator<_Dp, _IC>
      __find_bool(__bit_iterator<_Dp, _IC>, typename __size_difference_type_traits<_Dp>::size_type);
  template <bool _ToCount, class _Dp, bool _IC>
  friend typename __bit_iterator<_Dp, _IC>::difference_type _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
  __count_bool(__bit_iterator<_Dp, _IC>, typename __size_difference_type_traits<_Dp>::size_type);

  template <class, class...>
  friend struct __specialized_algorithm;
};

template <class _Cp>
struct __specialized_algorithm<_Algorithm::__fill_n, __single_iterator<__bit_iterator<_Cp, false> > > {
  static const bool __has_algorithm = true;

  template <bool _FillVal>
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static void
  __impl(__bit_iterator<_Cp, false> __first, typename __size_difference_type_traits<_Cp>::size_type __n) {
    using _It            = __bit_iterator<_Cp, false>;
    using __storage_type = typename _It::__storage_type;

    const int __bits_per_word = _It::__bits_per_word;
    // do first partial word
    if (__first.__ctz_ != 0) {
      __storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
      __storage_type __dn    = std::min(__clz_f, __n);
      std::__fill_masked_range(std::__to_address(__first.__seg_), __clz_f - __dn, __first.__ctz_, _FillVal);
      __n -= __dn;
      ++__first.__seg_;
    }
    // do middle whole words
    __storage_type __nw = __n / __bits_per_word;
    std::__fill_n(std::__to_address(__first.__seg_), __nw, _FillVal ? static_cast<__storage_type>(-1) : 0);
    __n -= __nw * __bits_per_word;
    // do last partial word
    if (__n > 0) {
      __first.__seg_ += __nw;
      std::__fill_masked_range(std::__to_address(__first.__seg_), __bits_per_word - __n, 0u, _FillVal);
    }
  }

  template <class _Size, class _Tp>
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static __bit_iterator<_Cp, false>
  operator()(__bit_iterator<_Cp, false> __first, _Size __n, const _Tp& __value) {
    if (__n <= 0)
      return __first;

    if (__value)
      __impl<true>(__first, __n);
    else
      __impl<false>(__first, __n);
    return __first + __n;
  }
};

template <class _Cp, bool _IsConst>
struct __specialized_algorithm<_Algorithm::__copy,
                               __iterator_pair<__bit_iterator<_Cp, _IsConst>, __bit_iterator<_Cp, _IsConst> >,
                               __single_iterator<__bit_iterator<_Cp, false> > > {
  static const bool __has_algorithm = true;

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static __bit_iterator<_Cp, false>
  __aligned_impl(__bit_iterator<_Cp, _IsConst> __first,
                 __bit_iterator<_Cp, _IsConst> __last,
                 __bit_iterator<_Cp, false> __result) {
    using _In             = __bit_iterator<_Cp, _IsConst>;
    using difference_type = typename _In::difference_type;
    using __storage_type  = typename _In::__storage_type;

    const int __bits_per_word = _In::__bits_per_word;
    difference_type __n       = __last - __first;
    if (__n > 0) {
      // do first word
      if (__first.__ctz_ != 0) {
        unsigned __clz       = __bits_per_word - __first.__ctz_;
        difference_type __dn = std::min(static_cast<difference_type>(__clz), __n);
        __n -= __dn;
        __storage_type __m = std::__middle_mask<__storage_type>(__clz - __dn, __first.__ctz_);
        __storage_type __b = *__first.__seg_ & __m;
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b;
        __result.__seg_ += (__dn + __result.__ctz_) / __bits_per_word;
        __result.__ctz_ = static_cast<unsigned>((__dn + __result.__ctz_) % __bits_per_word);
        ++__first.__seg_;
        // __first.__ctz_ = 0;
      }
      // __first.__ctz_ == 0;
      // do middle words
      __storage_type __nw = __n / __bits_per_word;
      std::copy(std::__to_address(__first.__seg_),
                std::__to_address(__first.__seg_ + __nw),
                std::__to_address(__result.__seg_));
      __n -= __nw * __bits_per_word;
      __result.__seg_ += __nw;
      // do last word
      if (__n > 0) {
        __first.__seg_ += __nw;
        __storage_type __m = std::__trailing_mask<__storage_type>(__bits_per_word - __n);
        __storage_type __b = *__first.__seg_ & __m;
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b;
        __result.__ctz_ = static_cast<unsigned>(__n);
      }
    }
    return __result;
  }

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 static __bit_iterator<_Cp, false>
  __unaligned_impl(__bit_iterator<_Cp, _IsConst> __first,
                   __bit_iterator<_Cp, _IsConst> __last,
                   __bit_iterator<_Cp, false> __result) {
    using _In             = __bit_iterator<_Cp, _IsConst>;
    using difference_type = typename _In::difference_type;
    using __storage_type  = typename _In::__storage_type;

    const int __bits_per_word = _In::__bits_per_word;
    difference_type __n       = __last - __first;
    if (__n > 0) {
      // do first word
      if (__first.__ctz_ != 0) {
        unsigned __clz_f     = __bits_per_word - __first.__ctz_;
        difference_type __dn = std::min(static_cast<difference_type>(__clz_f), __n);
        __n -= __dn;
        __storage_type __m   = std::__middle_mask<__storage_type>(__clz_f - __dn, __first.__ctz_);
        __storage_type __b   = *__first.__seg_ & __m;
        unsigned __clz_r     = __bits_per_word - __result.__ctz_;
        __storage_type __ddn = std::min<__storage_type>(__dn, __clz_r);
        __m                  = std::__middle_mask<__storage_type>(__clz_r - __ddn, __result.__ctz_);
        *__result.__seg_ &= ~__m;
        if (__result.__ctz_ > __first.__ctz_)
          *__result.__seg_ |= __b << (__result.__ctz_ - __first.__ctz_);
        else
          *__result.__seg_ |= __b >> (__first.__ctz_ - __result.__ctz_);
        __result.__seg_ += (__ddn + __result.__ctz_) / __bits_per_word;
        __result.__ctz_ = static_cast<unsigned>((__ddn + __result.__ctz_) % __bits_per_word);
        __dn -= __ddn;
        if (__dn > 0) {
          __m = std::__trailing_mask<__storage_type>(__bits_per_word - __dn);
          *__result.__seg_ &= ~__m;
          *__result.__seg_ |= __b >> (__first.__ctz_ + __ddn);
          __result.__ctz_ = static_cast<unsigned>(__dn);
        }
        ++__first.__seg_;
        // __first.__ctz_ = 0;
      }
      // __first.__ctz_ == 0;
      // do middle words
      unsigned __clz_r   = __bits_per_word - __result.__ctz_;
      __storage_type __m = std::__leading_mask<__storage_type>(__result.__ctz_);
      for (; __n >= __bits_per_word; __n -= __bits_per_word, ++__first.__seg_) {
        __storage_type __b = *__first.__seg_;
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b << __result.__ctz_;
        ++__result.__seg_;
        *__result.__seg_ &= __m;
        *__result.__seg_ |= __b >> __clz_r;
      }
      // do last word
      if (__n > 0) {
        __m                 = std::__trailing_mask<__storage_type>(__bits_per_word - __n);
        __storage_type __b  = *__first.__seg_ & __m;
        __storage_type __dn = std::min(__n, static_cast<difference_type>(__clz_r));
        __m                 = std::__middle_mask<__storage_type>(__clz_r - __dn, __result.__ctz_);
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b << __result.__ctz_;
        __result.__seg_ += (__dn + __result.__ctz_) / __bits_per_word;
        __result.__ctz_ = static_cast<unsigned>((__dn + __result.__ctz_) % __bits_per_word);
        __n -= __dn;
        if (__n > 0) {
          __m = std::__trailing_mask<__storage_type>(__bits_per_word - __n);
          *__result.__seg_ &= ~__m;
          *__result.__seg_ |= __b >> __dn;
          __result.__ctz_ = static_cast<unsigned>(__n);
        }
      }
    }
    return __result;
  }

  _LIBCPP_HIDE_FROM_ABI
  _LIBCPP_CONSTEXPR_SINCE_CXX20 static __in_out_result<__bit_iterator<_Cp, _IsConst>, __bit_iterator<_Cp, false> >
  operator()(__bit_iterator<_Cp, _IsConst> __first,
             __bit_iterator<_Cp, _IsConst> __last,
             __bit_iterator<_Cp, false> __result) {
    if (__first.__ctz_ == __result.__ctz_)
      return {__last, __aligned_impl(__first, __last, __result)};
    return {__last, __unaligned_impl(__first, __last, __result)};
  }
};

template <class _Cl, class _Cr>
struct __specialized_algorithm<_Algorithm::__swap_ranges,
                               __iterator_pair<__bit_iterator<_Cl, false>, __bit_iterator<_Cl, false> >,
                               __single_iterator<__bit_iterator<_Cr, false> > > {
  static const bool __has_algorithm = true;

  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator<_Cr, false> __aligned_impl(
      __bit_iterator<_Cl, false> __first, __bit_iterator<_Cl, false> __last, __bit_iterator<_Cr, false> __result) {
    using _I1             = __bit_iterator<_Cl, false>;
    using difference_type = typename _I1::difference_type;
    using __storage_type  = typename _I1::__storage_type;

    const int __bits_per_word = _I1::__bits_per_word;
    difference_type __n       = __last - __first;
    if (__n > 0) {
      // do first word
      if (__first.__ctz_ != 0) {
        unsigned __clz       = __bits_per_word - __first.__ctz_;
        difference_type __dn = std::min(static_cast<difference_type>(__clz), __n);
        __n -= __dn;
        __storage_type __m  = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz - __dn));
        __storage_type __b1 = *__first.__seg_ & __m;
        *__first.__seg_ &= ~__m;
        __storage_type __b2 = *__result.__seg_ & __m;
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b1;
        *__first.__seg_ |= __b2;
        __result.__seg_ += (__dn + __result.__ctz_) / __bits_per_word;
        __result.__ctz_ = static_cast<unsigned>((__dn + __result.__ctz_) % __bits_per_word);
        ++__first.__seg_;
        // __first.__ctz_ = 0;
      }
      // __first.__ctz_ == 0;
      // do middle words
      for (; __n >= __bits_per_word; __n -= __bits_per_word, ++__first.__seg_, ++__result.__seg_)
        swap(*__first.__seg_, *__result.__seg_);
      // do last word
      if (__n > 0) {
        __storage_type __m  = ~__storage_type(0) >> (__bits_per_word - __n);
        __storage_type __b1 = *__first.__seg_ & __m;
        *__first.__seg_ &= ~__m;
        __storage_type __b2 = *__result.__seg_ & __m;
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b1;
        *__first.__seg_ |= __b2;
        __result.__ctz_ = static_cast<unsigned>(__n);
      }
    }
    return __result;
  }

  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator<_Cr, false> __unaligned_impl(
      __bit_iterator<_Cl, false> __first, __bit_iterator<_Cl, false> __last, __bit_iterator<_Cr, false> __result) {
    using _I1             = __bit_iterator<_Cl, false>;
    using difference_type = typename _I1::difference_type;
    using __storage_type  = typename _I1::__storage_type;

    const int __bits_per_word = _I1::__bits_per_word;
    difference_type __n       = __last - __first;
    if (__n > 0) {
      // do first word
      if (__first.__ctz_ != 0) {
        unsigned __clz_f     = __bits_per_word - __first.__ctz_;
        difference_type __dn = std::min(static_cast<difference_type>(__clz_f), __n);
        __n -= __dn;
        __storage_type __m  = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
        __storage_type __b1 = *__first.__seg_ & __m;
        *__first.__seg_ &= ~__m;
        unsigned __clz_r     = __bits_per_word - __result.__ctz_;
        __storage_type __ddn = std::min<__storage_type>(__dn, __clz_r);
        __m                  = (~__storage_type(0) << __result.__ctz_) & (~__storage_type(0) >> (__clz_r - __ddn));
        __storage_type __b2  = *__result.__seg_ & __m;
        *__result.__seg_ &= ~__m;
        if (__result.__ctz_ > __first.__ctz_) {
          unsigned __s = __result.__ctz_ - __first.__ctz_;
          *__result.__seg_ |= __b1 << __s;
          *__first.__seg_ |= __b2 >> __s;
        } else {
          unsigned __s = __first.__ctz_ - __result.__ctz_;
          *__result.__seg_ |= __b1 >> __s;
          *__first.__seg_ |= __b2 << __s;
        }
        __result.__seg_ += (__ddn + __result.__ctz_) / __bits_per_word;
        __result.__ctz_ = static_cast<unsigned>((__ddn + __result.__ctz_) % __bits_per_word);
        __dn -= __ddn;
        if (__dn > 0) {
          __m  = ~__storage_type(0) >> (__bits_per_word - __dn);
          __b2 = *__result.__seg_ & __m;
          *__result.__seg_ &= ~__m;
          unsigned __s = __first.__ctz_ + __ddn;
          *__result.__seg_ |= __b1 >> __s;
          *__first.__seg_ |= __b2 << __s;
          __result.__ctz_ = static_cast<unsigned>(__dn);
        }
        ++__first.__seg_;
        // __first.__ctz_ = 0;
      }
      // __first.__ctz_ == 0;
      // do middle words
      __storage_type __m = ~__storage_type(0) << __result.__ctz_;
      unsigned __clz_r   = __bits_per_word - __result.__ctz_;
      for (; __n >= __bits_per_word; __n -= __bits_per_word, ++__first.__seg_) {
        __storage_type __b1 = *__first.__seg_;
        __storage_type __b2 = *__result.__seg_ & __m;
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b1 << __result.__ctz_;
        *__first.__seg_ = __b2 >> __result.__ctz_;
        ++__result.__seg_;
        __b2 = *__result.__seg_ & ~__m;
        *__result.__seg_ &= __m;
        *__result.__seg_ |= __b1 >> __clz_r;
        *__first.__seg_ |= __b2 << __clz_r;
      }
      // do last word
      if (__n > 0) {
        __m                 = ~__storage_type(0) >> (__bits_per_word - __n);
        __storage_type __b1 = *__first.__seg_ & __m;
        *__first.__seg_ &= ~__m;
        __storage_type __dn = std::min<__storage_type>(__n, __clz_r);
        __m                 = (~__storage_type(0) << __result.__ctz_) & (~__storage_type(0) >> (__clz_r - __dn));
        __storage_type __b2 = *__result.__seg_ & __m;
        *__result.__seg_ &= ~__m;
        *__result.__seg_ |= __b1 << __result.__ctz_;
        *__first.__seg_ |= __b2 >> __result.__ctz_;
        __result.__seg_ += (__dn + __result.__ctz_) / __bits_per_word;
        __result.__ctz_ = static_cast<unsigned>((__dn + __result.__ctz_) % __bits_per_word);
        __n -= __dn;
        if (__n > 0) {
          __m  = ~__storage_type(0) >> (__bits_per_word - __n);
          __b2 = *__result.__seg_ & __m;
          *__result.__seg_ &= ~__m;
          *__result.__seg_ |= __b1 >> __dn;
          *__first.__seg_ |= __b2 << __dn;
          __result.__ctz_ = static_cast<unsigned>(__n);
        }
      }
    }
    return __result;
  }

  _LIBCPP_HIDE_FROM_ABI static
      _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<__bit_iterator<_Cl, false>, __bit_iterator<_Cr, false> >
      operator()(__bit_iterator<_Cl, false> __first1,
                 __bit_iterator<_Cl, false> __last1,
                 __bit_iterator<_Cr, false> __first2) {
    if (__first1.__ctz_ == __first2.__ctz_)
      return std::make_pair(__last1, __aligned_impl(__first1, __last1, __first2));
    return std::make_pair(__last1, __unaligned_impl(__first1, __last1, __first2));
  }
};

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___BIT_REFERENCE