diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index 1d342cecbcc..614222db400 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -157,6 +157,7 @@ bits_headers = \
 	${bits_srcdir}/random.tcc \
 	${bits_srcdir}/range_access.h \
 	${bits_srcdir}/range_cmp.h \
+	${bits_srcdir}/ranges_algobase.h \
 	${bits_srcdir}/ranges_algo.h \
 	${bits_srcdir}/refwrap.h \
 	${bits_srcdir}/regex.h \
diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
index c735d67a5d3..7ee6a1e3f61 100644
--- a/libstdc++-v3/include/Makefile.in
+++ b/libstdc++-v3/include/Makefile.in
@@ -502,6 +502,7 @@ bits_headers = \
 	${bits_srcdir}/random.tcc \
 	${bits_srcdir}/range_access.h \
 	${bits_srcdir}/range_cmp.h \
+	${bits_srcdir}/ranges_algobase.h \
 	${bits_srcdir}/ranges_algo.h \
 	${bits_srcdir}/refwrap.h \
 	${bits_srcdir}/regex.h \
diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index e065ff2a974..84a02cabb80 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -32,13 +32,7 @@
 
 #if __cplusplus > 201703L
 
-#include <compare>
-#include <cmath>
-#include <iterator>
-// #include <bits/range_concepts.h>
-#include <ranges>
-#include <bits/invoke.h>
-#include <bits/cpp_type_traits.h> // __is_byte
+#include <bits/ranges_algobase.h>
 #include <bits/random.h> // concept uniform_random_bit_generator
 
 #if __cpp_lib_concepts
@@ -49,28 +43,6 @@ 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;
-
     template<typename _Comp, typename _Proj>
       constexpr auto
       __make_comp_proj(_Comp& __comp, _Proj& __proj)
@@ -741,420 +713,6 @@ namespace ranges
 				    std::move(__proj1), std::move(__proj2));
     }
 
-  template<input_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
-	   input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
-	   typename _Pred, typename _Proj1, typename _Proj2>
-    requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
-    constexpr bool
-    __equal(_Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2,
-	    _Pred __pred, _Proj1 __proj1, _Proj2 __proj2)
-    {
-      // TODO: implement more specializations to at least have parity with
-      // std::equal.
-      constexpr bool __sized_iters
-	= (sized_sentinel_for<_Sent1, _Iter1>
-	   && sized_sentinel_for<_Sent2, _Iter2>);
-      if constexpr (__sized_iters)
-	{
-	  auto __d1 = ranges::distance(__first1, __last1);
-	  auto __d2 = ranges::distance(__first2, __last2);
-	  if (__d1 != __d2)
-	    return false;
-
-	  using _ValueType1 = iter_value_t<_Iter1>;
-	  using _ValueType2 = iter_value_t<_Iter2>;
-	  constexpr bool __use_memcmp
-	    = ((is_integral_v<_ValueType1> || is_pointer_v<_ValueType1>)
-	       && is_same_v<_ValueType1, _ValueType2>
-	       && is_pointer_v<_Iter1>
-	       && is_pointer_v<_Iter2>
-	       && 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_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
-    equal(_Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2,
-	  _Pred __pred = {}, _Proj1 __proj1 = {}, _Proj2 __proj2 = {})
-    {
-      return ranges::__equal(std::__niter_base(std::move(__first1)),
-			     std::__niter_base(std::move(__last1)),
-			     std::__niter_base(std::move(__first2)),
-			     std::__niter_base(std::move(__last2)),
-			     std::move(__pred),
-			     std::move(__proj1), std::move(__proj2));
-    }
-
-  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
-    equal(_Range1&& __r1, _Range2&& __r2,
-	  _Pred __pred = {}, _Proj1 __proj1 = {}, _Proj2 __proj2 = {})
-    {
-      return ranges::equal(ranges::begin(__r1), ranges::end(__r1),
-			   ranges::begin(__r2), ranges::end(__r2),
-			   std::move(__pred),
-			   std::move(__proj1), std::move(__proj2));
-    }
-
-  template<typename _Iter, typename _Out>
-    struct copy_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>
-	operator copy_result<_Iter2, _Out2>() const &
-	{ return {in, out}; }
-
-      template<typename _Iter2, typename _Out2>
-	requires convertible_to<_Iter, _Iter2>
-	  && convertible_to<_Out, _Out2>
-	operator copy_result<_Iter2, _Out2>() &&
-	{ return {std::move(in), std::move(out)}; }
-    };
-
-  template<typename _Iter, typename _Out>
-    using move_result = copy_result<_Iter, _Out>;
-
-  template<typename _Iter1, typename _Iter2>
-    using move_backward_result = copy_result<_Iter1, _Iter2>;
-
-  template<typename _Iter1, typename _Iter2>
-    using copy_backward_result = copy_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.
-      constexpr bool __normal_iterator_p
-	= (__detail::__is_normal_iterator<_Iter>
-	   || __detail::__is_normal_iterator<_Out>);
-      constexpr bool __reverse_p
-	= (__detail::__is_reverse_iterator<_Iter>
-	   && __detail::__is_reverse_iterator<_Out>);
-      constexpr bool __move_iterator_p = __detail::__is_move_iterator<_Iter>;
-      if constexpr (__move_iterator_p)
-	{
-	  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 (__reverse_p)
-	{
-	  auto [__in,__out]
-	    = ranges::__copy_or_move_backward<_IsMove>(__last.base(),
-						       __first.base(),
-						       __result.base());
-	  return {reverse_iterator{std::move(__in)},
-		  reverse_iterator{std::move(__out)}};
-	}
-      else if constexpr (__normal_iterator_p)
-	{
-	  auto [__in,__out]
-	    = ranges::__copy_or_move<_IsMove>(std::__niter_base(__first),
-					      std::__niter_base(__last),
-					      std::__niter_base(__result));
-	  return {std::__niter_wrap(__first, std::move(__in)),
-		  std::__niter_wrap(__result, std::move(__out))};
-	}
-      else if constexpr (sized_sentinel_for<_Sent, _Iter>)
-	{
-	  using _ValueTypeI = iter_value_t<_Iter>;
-	  using _ValueTypeO = iter_value_t<_Out>;
-	  constexpr bool __use_memmove
-	    = (is_trivially_copyable_v<_ValueTypeI>
-	       && is_same_v<_ValueTypeI, _ValueTypeO>
-	       && is_pointer_v<_Iter>
-	       && is_pointer_v<_Out>);
-
-	  if constexpr (__use_memmove)
-	    {
-	      static_assert(_IsMove
-			    ? is_move_assignable_v<_ValueTypeI>
-			    : is_copy_assignable_v<_ValueTypeI>);
-	      auto __num = __last - __first;
-	      if (__num)
-		std::__memmove<_IsMove>(__result, __first, __num);
-	      return {__first + __num, __result + __num};
-	    }
-	  else
-	    {
-	      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)};
-	}
-    }
-
-  template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
-	   weakly_incrementable _Out>
-    requires indirectly_copyable<_Iter, _Out>
-    constexpr copy_result<_Iter, _Out>
-    copy(_Iter __first, _Sent __last, _Out __result)
-    {
-      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<safe_iterator_t<_Range>, _Out>
-    copy(_Range&& __r, _Out __result)
-    {
-      return ranges::copy(ranges::begin(__r), ranges::end(__r),
-			  std::move(__result));
-    }
-
-  template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
-	   weakly_incrementable _Out>
-    requires indirectly_movable<_Iter, _Out>
-    constexpr move_result<_Iter, _Out>
-    move(_Iter __first, _Sent __last, _Out __result)
-    {
-      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<safe_iterator_t<_Range>, _Out>
-    move(_Range&& __r, _Out __result)
-    {
-      return ranges::move(ranges::begin(__r), ranges::end(__r),
-			  std::move(__result));
-    }
-
-  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.
-      constexpr bool __normal_iterator_p
-	= (__detail::__is_normal_iterator<_Iter>
-	   || __detail::__is_normal_iterator<_Out>);
-      constexpr bool __reverse_p
-	= (__detail::__is_reverse_iterator<_Iter>
-	   && __detail::__is_reverse_iterator<_Out>);
-      if constexpr (__reverse_p)
-	{
-	  auto [__in,__out]
-	    = ranges::__copy_or_move<_IsMove>(__last.base(),
-					      __first.base(),
-					      __result.base());
-	  return {reverse_iterator{std::move(__in)},
-		  reverse_iterator{std::move(__out)}};
-	}
-      else if constexpr (__normal_iterator_p)
-	{
-	  auto [__in,__out]
-	    = ranges::__copy_or_move_backward<_IsMove>
-	      (std::__niter_base(__first),
-	       std::__niter_base(__last),
-	       std::__niter_base(__result));
-	  return {std::__niter_wrap(__first, std::move(__in)),
-		  std::__niter_wrap(__result, std::move(__out))};
-	}
-      else if constexpr (sized_sentinel_for<_Sent, _Iter>)
-	{
-	  using _ValueTypeI = iter_value_t<_Iter>;
-	  using _ValueTypeO = iter_value_t<_Out>;
-	  constexpr bool __use_memmove
-	    = (is_trivially_copyable_v<_ValueTypeI>
-	       && is_same_v<_ValueTypeI, _ValueTypeO>
-	       && is_pointer_v<_Iter>
-	       && is_pointer_v<_Out>);
-	  if constexpr (__use_memmove)
-	    {
-	      static_assert(_IsMove
-			    ? is_move_assignable_v<_ValueTypeI>
-			    : is_copy_assignable_v<_ValueTypeI>);
-	      auto __num = __last - __first;
-	      if (__num)
-		std::__memmove<_IsMove>(__result - __num, __first, __num);
-	      return {__first + __num, __result - __num};
-	    }
-	  else
-	    {
-	      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)};
-	}
-    }
-
-  template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
-	   bidirectional_iterator _Iter2>
-    requires indirectly_copyable<_Iter1, _Iter2>
-    constexpr copy_backward_result<_Iter1, _Iter2>
-    copy_backward(_Iter1 __first, _Sent1 __last, _Iter2 __result)
-    {
-      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<safe_iterator_t<_Range>, _Iter>
-    copy_backward(_Range&& __r, _Iter __result)
-    {
-      return ranges::copy_backward(ranges::begin(__r), ranges::end(__r),
-				   std::move(__result));
-    }
-
-  template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
-	   bidirectional_iterator _Iter2>
-    requires indirectly_movable<_Iter1, _Iter2>
-    constexpr move_backward_result<_Iter1, _Iter2>
-    move_backward(_Iter1 __first, _Sent1 __last, _Iter2 __result)
-    {
-      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<safe_iterator_t<_Range>, _Iter>
-    move_backward(_Range&& __r, _Iter __result)
-    {
-      return ranges::move_backward(ranges::begin(__r), ranges::end(__r),
-				   std::move(__result));
-    }
-
-  template<typename _Iter, typename _Out>
-    using copy_n_result = copy_result<_Iter, _Out>;
-
-  template<input_iterator _Iter, weakly_incrementable _Out>
-    requires indirectly_copyable<_Iter, _Out>
-    constexpr copy_n_result<_Iter, _Out>
-    copy_n(_Iter __first, iter_difference_t<_Iter> __n, _Out __result)
-    {
-      if constexpr (random_access_iterator<_Iter>)
-	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)};
-	}
-    }
-
   template<typename _Iter, typename _Out>
     using copy_if_result = copy_result<_Iter, _Out>;
 
@@ -1434,70 +992,6 @@ namespace ranges
 				     __new_value, std::move(__proj));
     }
 
-  template<typename _Tp, output_iterator<const _Tp&> _Out>
-    constexpr _Out
-    fill_n(_Out __first, iter_difference_t<_Out> __n, const _Tp& __value)
-    {
-      // TODO: implement more specializations to be at least on par with
-      // std::fill_n
-      if (__n <= 0)
-	return __first;
-
-      // TODO: is __is_byte the best condition?
-      if constexpr (is_pointer_v<_Out> && __is_byte<_Tp>::__value)
-	{
-	  __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;
-	}
-    }
-
-  template<typename _Tp,
-	   output_iterator<const _Tp&> _Out, sentinel_for<_Out> _Sent>
-    constexpr _Out
-    fill(_Out __first, _Sent __last, const _Tp& __value)
-    {
-      // 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 safe_iterator_t<_Range>
-    fill(_Range&& __r, const _Tp& __value)
-    {
-      return ranges::fill(ranges::begin(__r), ranges::end(__r), __value);
-    }
-
   template<input_or_output_iterator _Out, copy_constructible _Fp>
     requires invocable<_Fp&>
       && indirectly_writable<_Out, invoke_result_t<_Fp&>>
diff --git a/libstdc++-v3/include/bits/ranges_algobase.h b/libstdc++-v3/include/bits/ranges_algobase.h
new file mode 100644
index 00000000000..f63c032cf0b
--- /dev/null
+++ b/libstdc++-v3/include/bits/ranges_algobase.h
@@ -0,0 +1,556 @@
+// Core algorithmic facilities -*- C++ -*-
+
+// Copyright (C) 2020 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 <cmath>
+#include <compare>
+#include <iterator>
+// #include <bits/range_concepts.h>
+#include <ranges>
+#include <bits/invoke.h>
+#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
+
+  template<input_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
+	   input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
+	   typename _Pred, typename _Proj1, typename _Proj2>
+    requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
+    constexpr bool
+    __equal(_Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2,
+	    _Pred __pred, _Proj1 __proj1, _Proj2 __proj2)
+    {
+      // TODO: implement more specializations to at least have parity with
+      // std::equal.
+      constexpr bool __sized_iters
+	= (sized_sentinel_for<_Sent1, _Iter1>
+	   && sized_sentinel_for<_Sent2, _Iter2>);
+      if constexpr (__sized_iters)
+	{
+	  auto __d1 = ranges::distance(__first1, __last1);
+	  auto __d2 = ranges::distance(__first2, __last2);
+	  if (__d1 != __d2)
+	    return false;
+
+	  using _ValueType1 = iter_value_t<_Iter1>;
+	  using _ValueType2 = iter_value_t<_Iter2>;
+	  constexpr bool __use_memcmp
+	    = ((is_integral_v<_ValueType1> || is_pointer_v<_ValueType1>)
+	       && is_same_v<_ValueType1, _ValueType2>
+	       && is_pointer_v<_Iter1>
+	       && is_pointer_v<_Iter2>
+	       && 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_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
+    equal(_Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2,
+	  _Pred __pred = {}, _Proj1 __proj1 = {}, _Proj2 __proj2 = {})
+    {
+      return ranges::__equal(std::__niter_base(std::move(__first1)),
+			     std::__niter_base(std::move(__last1)),
+			     std::__niter_base(std::move(__first2)),
+			     std::__niter_base(std::move(__last2)),
+			     std::move(__pred),
+			     std::move(__proj1), std::move(__proj2));
+    }
+
+  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
+    equal(_Range1&& __r1, _Range2&& __r2,
+	  _Pred __pred = {}, _Proj1 __proj1 = {}, _Proj2 __proj2 = {})
+    {
+      return ranges::equal(ranges::begin(__r1), ranges::end(__r1),
+			   ranges::begin(__r2), ranges::end(__r2),
+			   std::move(__pred),
+			   std::move(__proj1), std::move(__proj2));
+    }
+
+  template<typename _Iter, typename _Out>
+    struct copy_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>
+	operator copy_result<_Iter2, _Out2>() const &
+	{ return {in, out}; }
+
+      template<typename _Iter2, typename _Out2>
+	requires convertible_to<_Iter, _Iter2>
+	  && convertible_to<_Out, _Out2>
+	operator copy_result<_Iter2, _Out2>() &&
+	{ return {std::move(in), std::move(out)}; }
+    };
+
+  template<typename _Iter, typename _Out>
+    using move_result = copy_result<_Iter, _Out>;
+
+  template<typename _Iter1, typename _Iter2>
+    using move_backward_result = copy_result<_Iter1, _Iter2>;
+
+  template<typename _Iter1, typename _Iter2>
+    using copy_backward_result = copy_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.
+      constexpr bool __normal_iterator_p
+	= (__detail::__is_normal_iterator<_Iter>
+	   || __detail::__is_normal_iterator<_Out>);
+      constexpr bool __reverse_p
+	= (__detail::__is_reverse_iterator<_Iter>
+	   && __detail::__is_reverse_iterator<_Out>);
+      constexpr bool __move_iterator_p = __detail::__is_move_iterator<_Iter>;
+      if constexpr (__move_iterator_p)
+	{
+	  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 (__reverse_p)
+	{
+	  auto [__in,__out]
+	    = ranges::__copy_or_move_backward<_IsMove>(__last.base(),
+						       __first.base(),
+						       __result.base());
+	  return {reverse_iterator{std::move(__in)},
+		  reverse_iterator{std::move(__out)}};
+	}
+      else if constexpr (__normal_iterator_p)
+	{
+	  auto [__in,__out]
+	    = ranges::__copy_or_move<_IsMove>(std::__niter_base(__first),
+					      std::__niter_base(__last),
+					      std::__niter_base(__result));
+	  return {std::__niter_wrap(__first, std::move(__in)),
+		  std::__niter_wrap(__result, std::move(__out))};
+	}
+      else if constexpr (sized_sentinel_for<_Sent, _Iter>)
+	{
+	  using _ValueTypeI = iter_value_t<_Iter>;
+	  using _ValueTypeO = iter_value_t<_Out>;
+	  constexpr bool __use_memmove
+	    = (is_trivially_copyable_v<_ValueTypeI>
+	       && is_same_v<_ValueTypeI, _ValueTypeO>
+	       && is_pointer_v<_Iter>
+	       && is_pointer_v<_Out>);
+
+	  if constexpr (__use_memmove)
+	    {
+	      static_assert(_IsMove
+			    ? is_move_assignable_v<_ValueTypeI>
+			    : is_copy_assignable_v<_ValueTypeI>);
+	      auto __num = __last - __first;
+	      if (__num)
+		std::__memmove<_IsMove>(__result, __first, __num);
+	      return {__first + __num, __result + __num};
+	    }
+	  else
+	    {
+	      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)};
+	}
+    }
+
+  template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
+	   weakly_incrementable _Out>
+    requires indirectly_copyable<_Iter, _Out>
+    constexpr copy_result<_Iter, _Out>
+    copy(_Iter __first, _Sent __last, _Out __result)
+    {
+      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<safe_iterator_t<_Range>, _Out>
+    copy(_Range&& __r, _Out __result)
+    {
+      return ranges::copy(ranges::begin(__r), ranges::end(__r),
+			  std::move(__result));
+    }
+
+  template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
+	   weakly_incrementable _Out>
+    requires indirectly_movable<_Iter, _Out>
+    constexpr move_result<_Iter, _Out>
+    move(_Iter __first, _Sent __last, _Out __result)
+    {
+      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<safe_iterator_t<_Range>, _Out>
+    move(_Range&& __r, _Out __result)
+    {
+      return ranges::move(ranges::begin(__r), ranges::end(__r),
+			  std::move(__result));
+    }
+
+  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.
+      constexpr bool __normal_iterator_p
+	= (__detail::__is_normal_iterator<_Iter>
+	   || __detail::__is_normal_iterator<_Out>);
+      constexpr bool __reverse_p
+	= (__detail::__is_reverse_iterator<_Iter>
+	   && __detail::__is_reverse_iterator<_Out>);
+      if constexpr (__reverse_p)
+	{
+	  auto [__in,__out]
+	    = ranges::__copy_or_move<_IsMove>(__last.base(),
+					      __first.base(),
+					      __result.base());
+	  return {reverse_iterator{std::move(__in)},
+		  reverse_iterator{std::move(__out)}};
+	}
+      else if constexpr (__normal_iterator_p)
+	{
+	  auto [__in,__out]
+	    = ranges::__copy_or_move_backward<_IsMove>
+	      (std::__niter_base(__first),
+	       std::__niter_base(__last),
+	       std::__niter_base(__result));
+	  return {std::__niter_wrap(__first, std::move(__in)),
+		  std::__niter_wrap(__result, std::move(__out))};
+	}
+      else if constexpr (sized_sentinel_for<_Sent, _Iter>)
+	{
+	  using _ValueTypeI = iter_value_t<_Iter>;
+	  using _ValueTypeO = iter_value_t<_Out>;
+	  constexpr bool __use_memmove
+	    = (is_trivially_copyable_v<_ValueTypeI>
+	       && is_same_v<_ValueTypeI, _ValueTypeO>
+	       && is_pointer_v<_Iter>
+	       && is_pointer_v<_Out>);
+	  if constexpr (__use_memmove)
+	    {
+	      static_assert(_IsMove
+			    ? is_move_assignable_v<_ValueTypeI>
+			    : is_copy_assignable_v<_ValueTypeI>);
+	      auto __num = __last - __first;
+	      if (__num)
+		std::__memmove<_IsMove>(__result - __num, __first, __num);
+	      return {__first + __num, __result - __num};
+	    }
+	  else
+	    {
+	      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)};
+	}
+    }
+
+  template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
+	   bidirectional_iterator _Iter2>
+    requires indirectly_copyable<_Iter1, _Iter2>
+    constexpr copy_backward_result<_Iter1, _Iter2>
+    copy_backward(_Iter1 __first, _Sent1 __last, _Iter2 __result)
+    {
+      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<safe_iterator_t<_Range>, _Iter>
+    copy_backward(_Range&& __r, _Iter __result)
+    {
+      return ranges::copy_backward(ranges::begin(__r), ranges::end(__r),
+				   std::move(__result));
+    }
+
+  template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
+	   bidirectional_iterator _Iter2>
+    requires indirectly_movable<_Iter1, _Iter2>
+    constexpr move_backward_result<_Iter1, _Iter2>
+    move_backward(_Iter1 __first, _Sent1 __last, _Iter2 __result)
+    {
+      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<safe_iterator_t<_Range>, _Iter>
+    move_backward(_Range&& __r, _Iter __result)
+    {
+      return ranges::move_backward(ranges::begin(__r), ranges::end(__r),
+				   std::move(__result));
+    }
+
+  template<typename _Iter, typename _Out>
+    using copy_n_result = copy_result<_Iter, _Out>;
+
+  template<input_iterator _Iter, weakly_incrementable _Out>
+    requires indirectly_copyable<_Iter, _Out>
+    constexpr copy_n_result<_Iter, _Out>
+    copy_n(_Iter __first, iter_difference_t<_Iter> __n, _Out __result)
+    {
+      if constexpr (random_access_iterator<_Iter>)
+	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)};
+	}
+    }
+
+  template<typename _Tp, output_iterator<const _Tp&> _Out>
+    constexpr _Out
+    fill_n(_Out __first, iter_difference_t<_Out> __n, const _Tp& __value)
+    {
+      // TODO: implement more specializations to be at least on par with
+      // std::fill_n
+      if (__n <= 0)
+	return __first;
+
+      // TODO: is __is_byte the best condition?
+      if constexpr (is_pointer_v<_Out> && __is_byte<_Tp>::__value)
+	{
+	  __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;
+	}
+    }
+
+  template<typename _Tp,
+	   output_iterator<const _Tp&> _Out, sentinel_for<_Out> _Sent>
+    constexpr _Out
+    fill(_Out __first, _Sent __last, const _Tp& __value)
+    {
+      // 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 safe_iterator_t<_Range>
+    fill(_Range&& __r, const _Tp& __value)
+    {
+      return ranges::fill(ranges::begin(__r), ranges::end(__r), __value);
+    }
+}
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+#endif // concepts
+#endif // C++20
+#endif // _RANGES_ALGOBASE_H
