libstdc++-v3/include/bits/ranges_algobase.h - gcc - Git at Google

 // Core algorithmic facilities -*- C++ -*-

 // Copyright (C) 2020-2021 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
 // terms of the GNU General Public License as published by the
 // Free Software Foundation; either version 3, or (at your option)
 // any later version.

 // This library is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 // GNU General Public License for more details.

 // Under Section 7 of GPL version 3, you are granted additional
 // permissions described in the GCC Runtime Library Exception, version
 // 3.1, as published by the Free Software Foundation.

 // You should have received a copy of the GNU General Public License and
 // a copy of the GCC Runtime Library Exception along with this program;
 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 // <http://www.gnu.org/licenses/>.

 /** @file bits/ranges_algobase.h
  *  This is an internal header file, included by other library headers.
  *  Do not attempt to use it directly. @headername{algorithm}
  */

 #ifndef _RANGES_ALGOBASE_H
 #define _RANGES_ALGOBASE_H 1

 #if __cplusplus > 201703L

 #include <compare>
 #include <iterator>
 #include <bits/ranges_base.h> // ranges::begin, ranges::range etc.
 #include <bits/invoke.h>      // __invoke
 #include <bits/cpp_type_traits.h> // __is_byte

 #if __cpp_lib_concepts
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 namespace ranges
 {
   namespace __detail
   {
     template<typename _Tp>
       constexpr inline bool __is_normal_iterator = false;

     template<typename _Iterator, typename _Container>
       constexpr inline bool
 	__is_normal_iterator<__gnu_cxx::__normal_iterator<_Iterator,
 							  _Container>> = true;

     template<typename _Tp>
       constexpr inline bool __is_reverse_iterator = false;

     template<typename _Iterator>
       constexpr inline bool
 	__is_reverse_iterator<reverse_iterator<_Iterator>> = true;

     template<typename _Tp>
       constexpr inline bool __is_move_iterator = false;

     template<typename _Iterator>
       constexpr inline bool
 	__is_move_iterator<move_iterator<_Iterator>> = true;
   } // namespace __detail

   struct __equal_fn
   {
     template<input_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
 	     input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
 	     typename _Pred = ranges::equal_to,
 	     typename _Proj1 = identity, typename _Proj2 = identity>
       requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
       constexpr bool
       operator()(_Iter1 __first1, _Sent1 __last1,
 		 _Iter2 __first2, _Sent2 __last2, _Pred __pred = {},
 		 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
       {
 	// TODO: implement more specializations to at least have parity with
 	// std::equal.
 	if constexpr (__detail::__is_normal_iterator<_Iter1>
 		      && same_as<_Iter1, _Sent1>)
 	  return (*this)(__first1.base(), __last1.base(),
 			 std::move(__first2), std::move(__last2),
 			 std::move(__pred),
 			 std::move(__proj1), std::move(__proj2));
 	else if constexpr (__detail::__is_normal_iterator<_Iter2>
 			   && same_as<_Iter2, _Sent2>)
 	  return (*this)(std::move(__first1), std::move(__last1),
 			 __first2.base(), __last2.base(),
 			 std::move(__pred),
 			 std::move(__proj1), std::move(__proj2));
 	else if constexpr (sized_sentinel_for<_Sent1, _Iter1>
 			   && sized_sentinel_for<_Sent2, _Iter2>)
 	  {
 	    auto __d1 = ranges::distance(__first1, __last1);
 	    auto __d2 = ranges::distance(__first2, __last2);
 	    if (__d1 != __d2)
 	      return false;

 	    using _ValueType1 = iter_value_t<_Iter1>;
 	    constexpr bool __use_memcmp
 	      = ((is_integral_v<_ValueType1> || is_pointer_v<_ValueType1>)
 		 && __memcmpable<_Iter1, _Iter2>::__value
 		 && is_same_v<_Pred, ranges::equal_to>
 		 && is_same_v<_Proj1, identity>
 		 && is_same_v<_Proj2, identity>);
 	    if constexpr (__use_memcmp)
 	      {
 		if (const size_t __len = (__last1 - __first1))
 		  return !std::__memcmp(__first1, __first2, __len);
 		return true;
 	      }
 	    else
 	      {
 		for (; __first1 != __last1; ++__first1, (void)++__first2)
 		  if (!(bool)std::__invoke(__pred,
 					   std::__invoke(__proj1, *__first1),
 					   std::__invoke(__proj2, *__first2)))
 		    return false;
 		return true;
 	      }
 	  }
 	else
 	  {
 	    for (; __first1 != __last1 && __first2 != __last2;
 		 ++__first1, (void)++__first2)
 	      if (!(bool)std::__invoke(__pred,
 				       std::__invoke(__proj1, *__first1),
 				       std::__invoke(__proj2, *__first2)))
 		return false;
 	    return __first1 == __last1 && __first2 == __last2;
 	  }
       }

     template<input_range _Range1, input_range _Range2,
 	     typename _Pred = ranges::equal_to,
 	     typename _Proj1 = identity, typename _Proj2 = identity>
       requires indirectly_comparable<iterator_t<_Range1>, iterator_t<_Range2>,
 				     _Pred, _Proj1, _Proj2>
       constexpr bool
       operator()(_Range1&& __r1, _Range2&& __r2, _Pred __pred = {},
 		 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
       {
 	return (*this)(ranges::begin(__r1), ranges::end(__r1),
 		       ranges::begin(__r2), ranges::end(__r2),
 		       std::move(__pred),
 		       std::move(__proj1), std::move(__proj2));
       }
   };

   inline constexpr __equal_fn equal{};

   template<typename _Iter, typename _Out>
     struct in_out_result
     {
       [[no_unique_address]] _Iter in;
       [[no_unique_address]] _Out out;

       template<typename _Iter2, typename _Out2>
 	requires convertible_to<const _Iter&, _Iter2>
 	  && convertible_to<const _Out&, _Out2>
 	constexpr
 	operator in_out_result<_Iter2, _Out2>() const &
 	{ return {in, out}; }

       template<typename _Iter2, typename _Out2>
 	requires convertible_to<_Iter, _Iter2>
 	  && convertible_to<_Out, _Out2>
 	constexpr
 	operator in_out_result<_Iter2, _Out2>() &&
 	{ return {std::move(in), std::move(out)}; }
     };

   template<typename _Iter, typename _Out>
     using copy_result = in_out_result<_Iter, _Out>;

   template<typename _Iter, typename _Out>
     using move_result = in_out_result<_Iter, _Out>;

   template<typename _Iter1, typename _Iter2>
     using move_backward_result = in_out_result<_Iter1, _Iter2>;

   template<typename _Iter1, typename _Iter2>
     using copy_backward_result = in_out_result<_Iter1, _Iter2>;

   template<bool _IsMove,
 	   bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
 	   bidirectional_iterator _Out>
     requires (_IsMove
 	      ? indirectly_movable<_Iter, _Out>
 	      : indirectly_copyable<_Iter, _Out>)
     constexpr conditional_t<_IsMove,
 			    move_backward_result<_Iter, _Out>,
 			    copy_backward_result<_Iter, _Out>>
     __copy_or_move_backward(_Iter __first, _Sent __last, _Out __result);

   template<bool _IsMove,
 	   input_iterator _Iter, sentinel_for<_Iter> _Sent,
 	   weakly_incrementable _Out>
     requires (_IsMove
 	      ? indirectly_movable<_Iter, _Out>
 	      : indirectly_copyable<_Iter, _Out>)
     constexpr conditional_t<_IsMove,
 			    move_result<_Iter, _Out>,
 			    copy_result<_Iter, _Out>>
     __copy_or_move(_Iter __first, _Sent __last, _Out __result)
     {
       // TODO: implement more specializations to be at least on par with
       // std::copy/std::move.
       using __detail::__is_move_iterator;
       using __detail::__is_reverse_iterator;
       using __detail::__is_normal_iterator;
       if constexpr (__is_move_iterator<_Iter> && same_as<_Iter, _Sent>)
 	{
 	  auto [__in, __out]
 	    = ranges::__copy_or_move<true>(std::move(__first).base(),
 					   std::move(__last).base(),
 					   std::move(__result));
 	  return {move_iterator{std::move(__in)}, std::move(__out)};
 	}
       else if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
 			 && __is_reverse_iterator<_Out>)
 	{
 	  auto [__in,__out]
 	    = ranges::__copy_or_move_backward<_IsMove>(std::move(__last).base(),
 						       std::move(__first).base(),
 						       std::move(__result).base());
 	  return {reverse_iterator{std::move(__in)},
 		  reverse_iterator{std::move(__out)}};
 	}
       else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
 	{
 	  auto [__in,__out]
 	    = ranges::__copy_or_move<_IsMove>(__first.base(), __last.base(),
 					      __result);
 	  return {decltype(__first){__in}, std::move(__out)};
 	}
       else if constexpr (__is_normal_iterator<_Out>)
 	{
 	  auto [__in,__out]
 	    = ranges::__copy_or_move<_IsMove>(std::move(__first), __last, __result.base());
 	  return {std::move(__in), decltype(__result){__out}};
 	}
       else if constexpr (sized_sentinel_for<_Sent, _Iter>)
 	{
 #ifdef __cpp_lib_is_constant_evaluated
 	  if (!std::is_constant_evaluated())
 #endif
 	    {
 	      if constexpr (__memcpyable<_Iter, _Out>::__value)
 		{
 		  using _ValueTypeI = iter_value_t<_Iter>;
 		  static_assert(_IsMove
 		      ? is_move_assignable_v<_ValueTypeI>
 		      : is_copy_assignable_v<_ValueTypeI>);
 		  auto __num = __last - __first;
 		  if (__num)
 		    __builtin_memmove(__result, __first,
 			sizeof(_ValueTypeI) * __num);
 		  return {__first + __num, __result + __num};
 		}
 	    }

 	  for (auto __n = __last - __first; __n > 0; --__n)
 	    {
 	      if constexpr (_IsMove)
 		*__result = std::move(*__first);
 	      else
 		*__result = *__first;
 	      ++__first;
 	      ++__result;
 	    }
 	  return {std::move(__first), std::move(__result)};
 	}
       else
 	{
 	  while (__first != __last)
 	    {
 	      if constexpr (_IsMove)
 		*__result = std::move(*__first);
 	      else
 		*__result = *__first;
 	      ++__first;
 	      ++__result;
 	    }
 	  return {std::move(__first), std::move(__result)};
 	}
     }

   struct __copy_fn
   {
     template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
 	     weakly_incrementable _Out>
       requires indirectly_copyable<_Iter, _Out>
       constexpr copy_result<_Iter, _Out>
       operator()(_Iter __first, _Sent __last, _Out __result) const
       {
 	return ranges::__copy_or_move<false>(std::move(__first),
 					     std::move(__last),
 					     std::move(__result));
       }

     template<input_range _Range, weakly_incrementable _Out>
       requires indirectly_copyable<iterator_t<_Range>, _Out>
       constexpr copy_result<borrowed_iterator_t<_Range>, _Out>
       operator()(_Range&& __r, _Out __result) const
       {
 	return (*this)(ranges::begin(__r), ranges::end(__r),
 		       std::move(__result));
       }
   };

   inline constexpr __copy_fn copy{};

   struct __move_fn
   {
     template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
 	     weakly_incrementable _Out>
       requires indirectly_movable<_Iter, _Out>
       constexpr move_result<_Iter, _Out>
       operator()(_Iter __first, _Sent __last, _Out __result) const
       {
 	return ranges::__copy_or_move<true>(std::move(__first),
 					    std::move(__last),
 					    std::move(__result));
       }

     template<input_range _Range, weakly_incrementable _Out>
       requires indirectly_movable<iterator_t<_Range>, _Out>
       constexpr move_result<borrowed_iterator_t<_Range>, _Out>
       operator()(_Range&& __r, _Out __result) const
       {
 	return (*this)(ranges::begin(__r), ranges::end(__r),
 		       std::move(__result));
       }
   };

   inline constexpr __move_fn move{};

   template<bool _IsMove,
 	   bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
 	   bidirectional_iterator _Out>
     requires (_IsMove
 	      ? indirectly_movable<_Iter, _Out>
 	      : indirectly_copyable<_Iter, _Out>)
     constexpr conditional_t<_IsMove,
 			    move_backward_result<_Iter, _Out>,
 			    copy_backward_result<_Iter, _Out>>
     __copy_or_move_backward(_Iter __first, _Sent __last, _Out __result)
     {
       // TODO: implement more specializations to be at least on par with
       // std::copy_backward/std::move_backward.
       using __detail::__is_reverse_iterator;
       using __detail::__is_normal_iterator;
       if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
 		    && __is_reverse_iterator<_Out>)
 	{
 	  auto [__in,__out]
 	    = ranges::__copy_or_move<_IsMove>(std::move(__last).base(),
 					      std::move(__first).base(),
 					      std::move(__result).base());
 	  return {reverse_iterator{std::move(__in)},
 		  reverse_iterator{std::move(__out)}};
 	}
       else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
 	{
 	  auto [__in,__out]
 	    = ranges::__copy_or_move_backward<_IsMove>(__first.base(),
 						       __last.base(),
 						       std::move(__result));
 	  return {decltype(__first){__in}, std::move(__out)};
 	}
       else if constexpr (__is_normal_iterator<_Out>)
 	{
 	  auto [__in,__out]
 	    = ranges::__copy_or_move_backward<_IsMove>(std::move(__first),
 						       std::move(__last),
 						       __result.base());
 	  return {std::move(__in), decltype(__result){__out}};
 	}
       else if constexpr (sized_sentinel_for<_Sent, _Iter>)
 	{
 #ifdef __cpp_lib_is_constant_evaluated
 	  if (!std::is_constant_evaluated())
 #endif
 	    {
 	      if constexpr (__memcpyable<_Out, _Iter>::__value)
 		{
 		  using _ValueTypeI = iter_value_t<_Iter>;
 		  static_assert(_IsMove
 		      ? is_move_assignable_v<_ValueTypeI>
 		      : is_copy_assignable_v<_ValueTypeI>);
 		  auto __num = __last - __first;
 		  if (__num)
 		    __builtin_memmove(__result - __num, __first,
 				      sizeof(_ValueTypeI) * __num);
 		  return {__first + __num, __result - __num};
 		}
 	    }

 	  auto __lasti = ranges::next(__first, __last);
 	  auto __tail = __lasti;

 	  for (auto __n = __last - __first; __n > 0; --__n)
 	    {
 	      --__tail;
 	      --__result;
 	      if constexpr (_IsMove)
 		*__result = std::move(*__tail);
 	      else
 		*__result = *__tail;
 	    }
 	  return {std::move(__lasti), std::move(__result)};
 	}
       else
 	{
 	  auto __lasti = ranges::next(__first, __last);
 	  auto __tail = __lasti;

 	  while (__first != __tail)
 	    {
 	      --__tail;
 	      --__result;
 	      if constexpr (_IsMove)
 		*__result = std::move(*__tail);
 	      else
 		*__result = *__tail;
 	    }
 	  return {std::move(__lasti), std::move(__result)};
 	}
     }

   struct __copy_backward_fn
   {
     template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
 	     bidirectional_iterator _Iter2>
       requires indirectly_copyable<_Iter1, _Iter2>
       constexpr copy_backward_result<_Iter1, _Iter2>
       operator()(_Iter1 __first, _Sent1 __last, _Iter2 __result) const
       {
 	return ranges::__copy_or_move_backward<false>(std::move(__first),
 						      std::move(__last),
 						      std::move(__result));
       }

     template<bidirectional_range _Range, bidirectional_iterator _Iter>
       requires indirectly_copyable<iterator_t<_Range>, _Iter>
       constexpr copy_backward_result<borrowed_iterator_t<_Range>, _Iter>
       operator()(_Range&& __r, _Iter __result) const
       {
 	return (*this)(ranges::begin(__r), ranges::end(__r),
 		       std::move(__result));
       }
   };

   inline constexpr __copy_backward_fn copy_backward{};

   struct __move_backward_fn
   {
     template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
 	     bidirectional_iterator _Iter2>
       requires indirectly_movable<_Iter1, _Iter2>
       constexpr move_backward_result<_Iter1, _Iter2>
       operator()(_Iter1 __first, _Sent1 __last, _Iter2 __result) const
       {
 	return ranges::__copy_or_move_backward<true>(std::move(__first),
 						     std::move(__last),
 						     std::move(__result));
       }

     template<bidirectional_range _Range, bidirectional_iterator _Iter>
       requires indirectly_movable<iterator_t<_Range>, _Iter>
       constexpr move_backward_result<borrowed_iterator_t<_Range>, _Iter>
       operator()(_Range&& __r, _Iter __result) const
       {
 	return (*this)(ranges::begin(__r), ranges::end(__r),
 		       std::move(__result));
       }
   };

   inline constexpr __move_backward_fn move_backward{};

   template<typename _Iter, typename _Out>
     using copy_n_result = in_out_result<_Iter, _Out>;

   struct __copy_n_fn
   {
     template<input_iterator _Iter, weakly_incrementable _Out>
       requires indirectly_copyable<_Iter, _Out>
       constexpr copy_n_result<_Iter, _Out>
       operator()(_Iter __first, iter_difference_t<_Iter> __n,
 		 _Out __result) const
       {
 	if constexpr (random_access_iterator<_Iter>)
 	  {
 	    if (__n > 0)
 	      return ranges::copy(__first, __first + __n, std::move(__result));
 	  }
 	else
 	  {
 	    for (; __n > 0; --__n, (void)++__result, (void)++__first)
 	      *__result = *__first;
 	  }
 	return {std::move(__first), std::move(__result)};
       }
   };

   inline constexpr __copy_n_fn copy_n{};

   struct __fill_n_fn
   {
     template<typename _Tp, output_iterator<const _Tp&> _Out>
       constexpr _Out
       operator()(_Out __first, iter_difference_t<_Out> __n,
 		 const _Tp& __value) const
       {
 	// TODO: implement more specializations to be at least on par with
 	// std::fill_n
 	if (__n <= 0)
 	  return __first;

 	// TODO: Generalize this optimization to contiguous iterators.
 	if constexpr (is_pointer_v<_Out>
 		      // Note that __is_byte already implies !is_volatile.
 		      && __is_byte<remove_pointer_t<_Out>>::__value
 		      && integral<_Tp>)
 	  {
 	    __builtin_memset(__first, static_cast<unsigned char>(__value), __n);
 	    return __first + __n;
 	  }
 	else if constexpr (is_scalar_v<_Tp>)
 	  {
 	    const auto __tmp = __value;
 	    for (; __n > 0; --__n, (void)++__first)
 	      *__first = __tmp;
 	    return __first;
 	  }
 	else
 	  {
 	    for (; __n > 0; --__n, (void)++__first)
 	      *__first = __value;
 	    return __first;
 	  }
       }
   };

   inline constexpr __fill_n_fn fill_n{};

   struct __fill_fn
   {
     template<typename _Tp,
 	     output_iterator<const _Tp&> _Out, sentinel_for<_Out> _Sent>
       constexpr _Out
       operator()(_Out __first, _Sent __last, const _Tp& __value) const
       {
 	// TODO: implement more specializations to be at least on par with
 	// std::fill
 	if constexpr (sized_sentinel_for<_Sent, _Out>)
 	  {
 	    const auto __len = __last - __first;
 	    return ranges::fill_n(__first, __len, __value);
 	  }
 	else if constexpr (is_scalar_v<_Tp>)
 	  {
 	    const auto __tmp = __value;
 	    for (; __first != __last; ++__first)
 	      *__first = __tmp;
 	    return __first;
 	  }
 	else
 	  {
 	    for (; __first != __last; ++__first)
 	      *__first = __value;
 	    return __first;
 	  }
       }

     template<typename _Tp, output_range<const _Tp&> _Range>
       constexpr borrowed_iterator_t<_Range>
       operator()(_Range&& __r, const _Tp& __value) const
       {
 	return (*this)(ranges::begin(__r), ranges::end(__r), __value);
       }
   };

   inline constexpr __fill_fn fill{};
 }
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
 #endif // concepts
 #endif // C++20
 #endif // _RANGES_ALGOBASE_H
	// Core algorithmic facilities -- C++ --

	// Copyright (C) 2020-2021 Free Software Foundation, Inc.
	//
	// This file is part of the GNU ISO C++ Library. This library is free
	// software; you can redistribute it and/or modify it under the
	// terms of the GNU General Public License as published by the
	// Free Software Foundation; either version 3, or (at your option)
	// any later version.

	// This library is distributed in the hope that it will be useful,
	// but WITHOUT ANY WARRANTY; without even the implied warranty of
	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	// GNU General Public License for more details.

	// Under Section 7 of GPL version 3, you are granted additional
	// permissions described in the GCC Runtime Library Exception, version
	// 3.1, as published by the Free Software Foundation.

	// You should have received a copy of the GNU General Public License and
	// a copy of the GCC Runtime Library Exception along with this program;
	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
	// <http://www.gnu.org/licenses/>.

	/** @file bits/ranges_algobase.h
	* This is an internal header file, included by other library headers.
	* Do not attempt to use it directly. @headername{algorithm}
	*/

	#ifndef _RANGES_ALGOBASE_H
	#define _RANGES_ALGOBASE_H 1

	#if __cplusplus > 201703L

	#include <compare>
	#include <iterator>
	#include <bits/ranges_base.h> // ranges::begin, ranges::range etc.
	#include <bits/invoke.h> // __invoke
	#include <bits/cpp_type_traits.h> // __is_byte

	#if __cpp_lib_concepts
	namespace std _GLIBCXX_VISIBILITY(default)
	{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION
	namespace ranges
	{
	namespace __detail
	{
	template<typename _Tp>
	constexpr inline bool __is_normal_iterator = false;

	template<typename _Iterator, typename _Container>
	constexpr inline bool
	__is_normal_iterator<__gnu_cxx::__normal_iterator<_Iterator,
	_Container>> = true;

	template<typename _Tp>
	constexpr inline bool __is_reverse_iterator = false;

	template<typename _Iterator>
	constexpr inline bool
	__is_reverse_iterator<reverse_iterator<_Iterator>> = true;

	template<typename _Tp>
	constexpr inline bool __is_move_iterator = false;

	template<typename _Iterator>
	constexpr inline bool
	__is_move_iterator<move_iterator<_Iterator>> = true;
	} // namespace __detail

	struct __equal_fn
	{
	template<input_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
	input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
	typename _Pred = ranges::equal_to,
	typename _Proj1 = identity, typename _Proj2 = identity>
	requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
	constexpr bool
	operator()(_Iter1 __first1, _Sent1 __last1,
	_Iter2 __first2, _Sent2 __last2, _Pred __pred = {},
	_Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
	{
	// TODO: implement more specializations to at least have parity with
	// std::equal.
	if constexpr (__detail::__is_normal_iterator<_Iter1>
	&& same_as<_Iter1, _Sent1>)
	return (*this)(__first1.base(), __last1.base(),
	std::move(__first2), std::move(__last2),
	std::move(__pred),
	std::move(__proj1), std::move(__proj2));
	else if constexpr (__detail::__is_normal_iterator<_Iter2>
	&& same_as<_Iter2, _Sent2>)
	return (*this)(std::move(__first1), std::move(__last1),
	__first2.base(), __last2.base(),
	std::move(__pred),
	std::move(__proj1), std::move(__proj2));
	else if constexpr (sized_sentinel_for<_Sent1, _Iter1>
	&& sized_sentinel_for<_Sent2, _Iter2>)
	{
	auto __d1 = ranges::distance(__first1, __last1);
	auto __d2 = ranges::distance(__first2, __last2);
	if (__d1 != __d2)
	return false;

	using _ValueType1 = iter_value_t<_Iter1>;
	constexpr bool __use_memcmp
	= ((is_integral_v<_ValueType1> \|\| is_pointer_v<_ValueType1>)
	&& __memcmpable<_Iter1, _Iter2>::__value
	&& is_same_v<_Pred, ranges::equal_to>
	&& is_same_v<_Proj1, identity>
	&& is_same_v<_Proj2, identity>);
	if constexpr (__use_memcmp)
	{
	if (const size_t __len = (__last1 - __first1))
	return !std::__memcmp(__first1, __first2, __len);
	return true;
	}
	else
	{
	for (; __first1 != __last1; ++__first1, (void)++__first2)
	if (!(bool)std::__invoke(__pred,
	std::__invoke(__proj1, *__first1),
	std::__invoke(__proj2, *__first2)))
	return false;
	return true;
	}
	}
	else
	{
	for (; __first1 != __last1 && __first2 != __last2;
	++__first1, (void)++__first2)
	if (!(bool)std::__invoke(__pred,
	std::__invoke(__proj1, *__first1),
	std::__invoke(__proj2, *__first2)))
	return false;
	return __first1 == __last1 && __first2 == __last2;
	}
	}

	template<input_range _Range1, input_range _Range2,
	typename _Pred = ranges::equal_to,
	typename _Proj1 = identity, typename _Proj2 = identity>
	requires indirectly_comparable<iterator_t<_Range1>, iterator_t<_Range2>,
	_Pred, _Proj1, _Proj2>
	constexpr bool
	operator()(_Range1&& __r1, _Range2&& __r2, _Pred __pred = {},
	_Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
	{
	return (*this)(ranges::begin(__r1), ranges::end(__r1),
	ranges::begin(__r2), ranges::end(__r2),
	std::move(__pred),
	std::move(__proj1), std::move(__proj2));
	}
	};

	inline constexpr __equal_fn equal{};

	template<typename _Iter, typename _Out>
	struct in_out_result
	{
	[[no_unique_address]] _Iter in;
	[[no_unique_address]] _Out out;

	template<typename _Iter2, typename _Out2>
	requires convertible_to<const _Iter&, _Iter2>
	&& convertible_to<const _Out&, _Out2>
	constexpr
	operator in_out_result<_Iter2, _Out2>() const &
	{ return {in, out}; }

	template<typename _Iter2, typename _Out2>
	requires convertible_to<_Iter, _Iter2>
	&& convertible_to<_Out, _Out2>
	constexpr
	operator in_out_result<_Iter2, _Out2>() &&
	{ return {std::move(in), std::move(out)}; }
	};

	template<typename _Iter, typename _Out>
	using copy_result = in_out_result<_Iter, _Out>;

	template<typename _Iter, typename _Out>
	using move_result = in_out_result<_Iter, _Out>;

	template<typename _Iter1, typename _Iter2>
	using move_backward_result = in_out_result<_Iter1, _Iter2>;

	template<typename _Iter1, typename _Iter2>
	using copy_backward_result = in_out_result<_Iter1, _Iter2>;

	template<bool _IsMove,
	bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
	bidirectional_iterator _Out>
	requires (_IsMove
	? indirectly_movable<_Iter, _Out>
	: indirectly_copyable<_Iter, _Out>)
	constexpr conditional_t<_IsMove,
	move_backward_result<_Iter, _Out>,
	copy_backward_result<_Iter, _Out>>
	__copy_or_move_backward(_Iter __first, _Sent __last, _Out __result);

	template<bool _IsMove,
	input_iterator _Iter, sentinel_for<_Iter> _Sent,
	weakly_incrementable _Out>
	requires (_IsMove
	? indirectly_movable<_Iter, _Out>
	: indirectly_copyable<_Iter, _Out>)
	constexpr conditional_t<_IsMove,
	move_result<_Iter, _Out>,
	copy_result<_Iter, _Out>>
	__copy_or_move(_Iter __first, _Sent __last, _Out __result)
	{
	// TODO: implement more specializations to be at least on par with
	// std::copy/std::move.
	using __detail::__is_move_iterator;
	using __detail::__is_reverse_iterator;
	using __detail::__is_normal_iterator;
	if constexpr (__is_move_iterator<_Iter> && same_as<_Iter, _Sent>)
	{
	auto [__in, __out]
	= ranges::__copy_or_move<true>(std::move(__first).base(),
	std::move(__last).base(),
	std::move(__result));
	return {move_iterator{std::move(__in)}, std::move(__out)};
	}
	else if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
	&& __is_reverse_iterator<_Out>)
	{
	auto [__in,__out]
	= ranges::__copy_or_move_backward<_IsMove>(std::move(__last).base(),
	std::move(__first).base(),
	std::move(__result).base());
	return {reverse_iterator{std::move(__in)},
	reverse_iterator{std::move(__out)}};
	}
	else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
	{
	auto [__in,__out]
	= ranges::__copy_or_move<_IsMove>(__first.base(), __last.base(),
	__result);
	return {decltype(__first){__in}, std::move(__out)};
	}
	else if constexpr (__is_normal_iterator<_Out>)
	{
	auto [__in,__out]
	= ranges::__copy_or_move<_IsMove>(std::move(__first), __last, __result.base());
	return {std::move(__in), decltype(__result){__out}};
	}
	else if constexpr (sized_sentinel_for<_Sent, _Iter>)
	{
	#ifdef __cpp_lib_is_constant_evaluated
	if (!std::is_constant_evaluated())
	#endif
	{
	if constexpr (__memcpyable<_Iter, _Out>::__value)
	{
	using _ValueTypeI = iter_value_t<_Iter>;
	static_assert(_IsMove
	? is_move_assignable_v<_ValueTypeI>
	: is_copy_assignable_v<_ValueTypeI>);
	auto __num = __last - __first;
	if (__num)
	__builtin_memmove(__result, __first,
	sizeof(_ValueTypeI) * __num);
	return {__first + __num, __result + __num};
	}
	}

	for (auto __n = __last - __first; __n > 0; --__n)
	{
	if constexpr (_IsMove)
	__result = std::move(__first);
	else
	__result = __first;
	++__first;
	++__result;
	}
	return {std::move(__first), std::move(__result)};
	}
	else
	{
	while (__first != __last)
	{
	if constexpr (_IsMove)
	__result = std::move(__first);
	else
	__result = __first;
	++__first;
	++__result;
	}
	return {std::move(__first), std::move(__result)};
	}
	}

	struct __copy_fn
	{
	template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
	weakly_incrementable _Out>
	requires indirectly_copyable<_Iter, _Out>
	constexpr copy_result<_Iter, _Out>
	operator()(_Iter __first, _Sent __last, _Out __result) const
	{
	return ranges::__copy_or_move<false>(std::move(__first),
	std::move(__last),
	std::move(__result));
	}

	template<input_range _Range, weakly_incrementable _Out>
	requires indirectly_copyable<iterator_t<_Range>, _Out>
	constexpr copy_result<borrowed_iterator_t<_Range>, _Out>
	operator()(_Range&& __r, _Out __result) const
	{
	return (*this)(ranges::begin(__r), ranges::end(__r),
	std::move(__result));
	}
	};

	inline constexpr __copy_fn copy{};

	struct __move_fn
	{
	template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
	weakly_incrementable _Out>
	requires indirectly_movable<_Iter, _Out>
	constexpr move_result<_Iter, _Out>
	operator()(_Iter __first, _Sent __last, _Out __result) const
	{
	return ranges::__copy_or_move<true>(std::move(__first),
	std::move(__last),
	std::move(__result));
	}

	template<input_range _Range, weakly_incrementable _Out>
	requires indirectly_movable<iterator_t<_Range>, _Out>
	constexpr move_result<borrowed_iterator_t<_Range>, _Out>
	operator()(_Range&& __r, _Out __result) const
	{
	return (*this)(ranges::begin(__r), ranges::end(__r),
	std::move(__result));
	}
	};

	inline constexpr __move_fn move{};

	template<bool _IsMove,
	bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
	bidirectional_iterator _Out>
	requires (_IsMove
	? indirectly_movable<_Iter, _Out>
	: indirectly_copyable<_Iter, _Out>)
	constexpr conditional_t<_IsMove,
	move_backward_result<_Iter, _Out>,
	copy_backward_result<_Iter, _Out>>
	__copy_or_move_backward(_Iter __first, _Sent __last, _Out __result)
	{
	// TODO: implement more specializations to be at least on par with
	// std::copy_backward/std::move_backward.
	using __detail::__is_reverse_iterator;
	using __detail::__is_normal_iterator;
	if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
	&& __is_reverse_iterator<_Out>)
	{
	auto [__in,__out]
	= ranges::__copy_or_move<_IsMove>(std::move(__last).base(),
	std::move(__first).base(),
	std::move(__result).base());
	return {reverse_iterator{std::move(__in)},
	reverse_iterator{std::move(__out)}};
	}
	else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
	{
	auto [__in,__out]
	= ranges::__copy_or_move_backward<_IsMove>(__first.base(),
	__last.base(),
	std::move(__result));
	return {decltype(__first){__in}, std::move(__out)};
	}
	else if constexpr (__is_normal_iterator<_Out>)
	{
	auto [__in,__out]
	= ranges::__copy_or_move_backward<_IsMove>(std::move(__first),
	std::move(__last),
	__result.base());
	return {std::move(__in), decltype(__result){__out}};
	}
	else if constexpr (sized_sentinel_for<_Sent, _Iter>)
	{
	#ifdef __cpp_lib_is_constant_evaluated
	if (!std::is_constant_evaluated())
	#endif
	{
	if constexpr (__memcpyable<_Out, _Iter>::__value)
	{
	using _ValueTypeI = iter_value_t<_Iter>;
	static_assert(_IsMove
	? is_move_assignable_v<_ValueTypeI>
	: is_copy_assignable_v<_ValueTypeI>);
	auto __num = __last - __first;
	if (__num)
	__builtin_memmove(__result - __num, __first,
	sizeof(_ValueTypeI) * __num);
	return {__first + __num, __result - __num};
	}
	}

	auto __lasti = ranges::next(__first, __last);
	auto __tail = __lasti;

	for (auto __n = __last - __first; __n > 0; --__n)
	{
	--__tail;
	--__result;
	if constexpr (_IsMove)
	__result = std::move(__tail);
	else
	__result = __tail;
	}
	return {std::move(__lasti), std::move(__result)};
	}
	else
	{
	auto __lasti = ranges::next(__first, __last);
	auto __tail = __lasti;

	while (__first != __tail)
	{
	--__tail;
	--__result;
	if constexpr (_IsMove)
	__result = std::move(__tail);
	else
	__result = __tail;
	}
	return {std::move(__lasti), std::move(__result)};
	}
	}

	struct __copy_backward_fn
	{
	template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
	bidirectional_iterator _Iter2>
	requires indirectly_copyable<_Iter1, _Iter2>
	constexpr copy_backward_result<_Iter1, _Iter2>
	operator()(_Iter1 __first, _Sent1 __last, _Iter2 __result) const
	{
	return ranges::__copy_or_move_backward<false>(std::move(__first),
	std::move(__last),
	std::move(__result));
	}

	template<bidirectional_range _Range, bidirectional_iterator _Iter>
	requires indirectly_copyable<iterator_t<_Range>, _Iter>
	constexpr copy_backward_result<borrowed_iterator_t<_Range>, _Iter>
	operator()(_Range&& __r, _Iter __result) const
	{
	return (*this)(ranges::begin(__r), ranges::end(__r),
	std::move(__result));
	}
	};

	inline constexpr __copy_backward_fn copy_backward{};

	struct __move_backward_fn
	{
	template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
	bidirectional_iterator _Iter2>
	requires indirectly_movable<_Iter1, _Iter2>
	constexpr move_backward_result<_Iter1, _Iter2>
	operator()(_Iter1 __first, _Sent1 __last, _Iter2 __result) const
	{
	return ranges::__copy_or_move_backward<true>(std::move(__first),
	std::move(__last),
	std::move(__result));
	}

	template<bidirectional_range _Range, bidirectional_iterator _Iter>
	requires indirectly_movable<iterator_t<_Range>, _Iter>
	constexpr move_backward_result<borrowed_iterator_t<_Range>, _Iter>
	operator()(_Range&& __r, _Iter __result) const
	{
	return (*this)(ranges::begin(__r), ranges::end(__r),
	std::move(__result));
	}
	};

	inline constexpr __move_backward_fn move_backward{};

	template<typename _Iter, typename _Out>
	using copy_n_result = in_out_result<_Iter, _Out>;

	struct __copy_n_fn
	{
	template<input_iterator _Iter, weakly_incrementable _Out>
	requires indirectly_copyable<_Iter, _Out>
	constexpr copy_n_result<_Iter, _Out>
	operator()(_Iter __first, iter_difference_t<_Iter> __n,
	_Out __result) const
	{
	if constexpr (random_access_iterator<_Iter>)
	{
	if (__n > 0)
	return ranges::copy(__first, __first + __n, std::move(__result));
	}
	else
	{
	for (; __n > 0; --__n, (void)++__result, (void)++__first)
	__result = __first;
	}
	return {std::move(__first), std::move(__result)};
	}
	};

	inline constexpr __copy_n_fn copy_n{};

	struct __fill_n_fn
	{
	template<typename _Tp, output_iterator<const _Tp&> _Out>
	constexpr _Out
	operator()(_Out __first, iter_difference_t<_Out> __n,
	const _Tp& __value) const
	{
	// TODO: implement more specializations to be at least on par with
	// std::fill_n
	if (__n <= 0)
	return __first;

	// TODO: Generalize this optimization to contiguous iterators.
	if constexpr (is_pointer_v<_Out>
	// Note that __is_byte already implies !is_volatile.
	&& __is_byte<remove_pointer_t<_Out>>::__value
	&& integral<_Tp>)
	{
	__builtin_memset(__first, static_cast<unsigned char>(__value), __n);
	return __first + __n;
	}
	else if constexpr (is_scalar_v<_Tp>)
	{
	const auto __tmp = __value;
	for (; __n > 0; --__n, (void)++__first)
	*__first = __tmp;
	return __first;
	}
	else
	{
	for (; __n > 0; --__n, (void)++__first)
	*__first = __value;
	return __first;
	}
	}
	};

	inline constexpr __fill_n_fn fill_n{};

	struct __fill_fn
	{
	template<typename _Tp,
	output_iterator<const _Tp&> _Out, sentinel_for<_Out> _Sent>
	constexpr _Out
	operator()(_Out __first, _Sent __last, const _Tp& __value) const
	{
	// TODO: implement more specializations to be at least on par with
	// std::fill
	if constexpr (sized_sentinel_for<_Sent, _Out>)
	{
	const auto __len = __last - __first;
	return ranges::fill_n(__first, __len, __value);
	}
	else if constexpr (is_scalar_v<_Tp>)
	{
	const auto __tmp = __value;
	for (; __first != __last; ++__first)
	*__first = __tmp;
	return __first;
	}
	else
	{
	for (; __first != __last; ++__first)
	*__first = __value;
	return __first;
	}
	}

	template<typename _Tp, output_range<const _Tp&> _Range>
	constexpr borrowed_iterator_t<_Range>
	operator()(_Range&& __r, const _Tp& __value) const
	{
	return (*this)(ranges::begin(__r), ranges::end(__r), __value);
	}
	};

	inline constexpr __fill_fn fill{};
	}
	_GLIBCXX_END_NAMESPACE_VERSION
	} // namespace std
	#endif // concepts
	#endif // C++20
	#endif // _RANGES_ALGOBASE_H