--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libstdc++-v3/include/bits/range_cmp.h	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,192 @@
+// Concept-constrained comparison implementations -*- C++ -*-
+
+// Copyright (C) 2019-2020 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/range_cmp.h
+ *  This is an internal header file, included by other library headers.
+ *  Do not attempt to use it directly. @headername{functional}
+ */
+
+#ifndef _RANGE_CMP_H
+#define _RANGE_CMP_H 1
+
+#if __cplusplus > 201703L
+# include <bits/move.h>
+# include <concepts>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  struct __is_transparent; // not defined
+
+  // Define std::identity here so that <iterator> and <ranges>
+  // don't need to include <bits/stl_function.h> to get it.
+
+  /// [func.identity] The identity function.
+  struct identity
+  {
+    template<typename _Tp>
+      constexpr _Tp&&
+      operator()(_Tp&& __t) const noexcept
+      { return std::forward<_Tp>(__t); }
+
+    using is_transparent = __is_transparent;
+  };
+
+#ifdef __cpp_lib_concepts
+namespace ranges
+{
+  namespace __detail
+  {
+    // BUILTIN-PTR-CMP(T, ==, U)
+    template<typename _Tp, typename _Up>
+      concept __eq_builtin_ptr_cmp
+	= requires (_Tp&& __t, _Up&& __u) { { __t == __u } -> same_as<bool>; }
+	  && convertible_to<_Tp, const volatile void*>
+	  && convertible_to<_Up, const volatile void*>
+	  && (! requires(_Tp&& __t, _Up&& __u)
+	      { operator==(std::forward<_Tp>(__t), std::forward<_Up>(__u)); }
+	      &&
+	      ! requires(_Tp&& __t, _Up&& __u)
+	      { std::forward<_Tp>(__t).operator==(std::forward<_Up>(__u)); });
+
+    // BUILTIN-PTR-CMP(T, <, U)
+    template<typename _Tp, typename _Up>
+      concept __less_builtin_ptr_cmp
+	= requires (_Tp&& __t, _Up&& __u) { { __t < __u } -> same_as<bool>; }
+	  && convertible_to<_Tp, const volatile void*>
+	  && convertible_to<_Up, const volatile void*>
+	  && (! requires(_Tp&& __t, _Up&& __u)
+	      { operator<(std::forward<_Tp>(__t), std::forward<_Up>(__u)); }
+	      && ! requires(_Tp&& __t, _Up&& __u)
+	      { std::forward<_Tp>(__t).operator<(std::forward<_Up>(__u)); });
+  } // namespace __detail
+
+  // [range.cmp] Concept-constrained comparisons
+
+  /// ranges::equal_to function object type.
+  struct equal_to
+  {
+    template<typename _Tp, typename _Up>
+      requires equality_comparable_with<_Tp, _Up>
+	|| __detail::__eq_builtin_ptr_cmp<_Tp, _Up>
+      constexpr bool
+      operator()(_Tp&& __t, _Up&& __u) const
+      noexcept(noexcept(std::declval<_Tp>() == std::declval<_Up>()))
+      { return std::forward<_Tp>(__t) == std::forward<_Up>(__u); }
+
+    using is_transparent = __is_transparent;
+  };
+
+  /// ranges::not_equal_to function object type.
+  struct not_equal_to
+  {
+    template<typename _Tp, typename _Up>
+      requires equality_comparable_with<_Tp, _Up>
+	|| __detail::__eq_builtin_ptr_cmp<_Tp, _Up>
+      constexpr bool
+      operator()(_Tp&& __t, _Up&& __u) const
+      noexcept(noexcept(std::declval<_Up>() == std::declval<_Tp>()))
+      { return !equal_to{}(std::forward<_Tp>(__t), std::forward<_Up>(__u)); }
+
+    using is_transparent = __is_transparent;
+  };
+
+  /// ranges::less function object type.
+  struct less
+  {
+    template<typename _Tp, typename _Up>
+      requires totally_ordered_with<_Tp, _Up>
+	|| __detail::__less_builtin_ptr_cmp<_Tp, _Up>
+      constexpr bool
+      operator()(_Tp&& __t, _Up&& __u) const
+      noexcept(noexcept(std::declval<_Tp>() < std::declval<_Up>()))
+      {
+	if constexpr (__detail::__less_builtin_ptr_cmp<_Tp, _Up>)
+	  {
+#ifdef __cpp_lib_is_constant_evaluated
+	    if (std::is_constant_evaluated())
+	      return __t < __u;
+#endif
+	    auto __x = reinterpret_cast<__UINTPTR_TYPE__>(
+	      static_cast<const volatile void*>(std::forward<_Tp>(__t)));
+	    auto __y = reinterpret_cast<__UINTPTR_TYPE__>(
+	      static_cast<const volatile void*>(std::forward<_Up>(__u)));
+	    return __x < __y;
+	  }
+	else
+	  return std::forward<_Tp>(__t) < std::forward<_Up>(__u);
+      }
+
+    using is_transparent = __is_transparent;
+  };
+
+  /// ranges::greater function object type.
+  struct greater
+  {
+    template<typename _Tp, typename _Up>
+      requires totally_ordered_with<_Tp, _Up>
+	|| __detail::__less_builtin_ptr_cmp<_Up, _Tp>
+      constexpr bool
+      operator()(_Tp&& __t, _Up&& __u) const
+      noexcept(noexcept(std::declval<_Up>() < std::declval<_Tp>()))
+      { return less{}(std::forward<_Up>(__u), std::forward<_Tp>(__t)); }
+
+    using is_transparent = __is_transparent;
+  };
+
+  /// ranges::greater_equal function object type.
+  struct greater_equal
+  {
+    template<typename _Tp, typename _Up>
+      requires totally_ordered_with<_Tp, _Up>
+	|| __detail::__less_builtin_ptr_cmp<_Tp, _Up>
+      constexpr bool
+      operator()(_Tp&& __t, _Up&& __u) const
+      noexcept(noexcept(std::declval<_Tp>() < std::declval<_Up>()))
+      { return !less{}(std::forward<_Tp>(__t), std::forward<_Up>(__u)); }
+
+    using is_transparent = __is_transparent;
+  };
+
+  /// ranges::less_equal function object type.
+  struct less_equal
+  {
+    template<typename _Tp, typename _Up>
+      requires totally_ordered_with<_Tp, _Up>
+	|| __detail::__less_builtin_ptr_cmp<_Up, _Tp>
+      constexpr bool
+      operator()(_Tp&& __t, _Up&& __u) const
+      noexcept(noexcept(std::declval<_Up>() < std::declval<_Tp>()))
+      { return !less{}(std::forward<_Up>(__u), std::forward<_Tp>(__t)); }
+
+    using is_transparent = __is_transparent;
+  };
+
+} // namespace ranges
+#endif // library concepts
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+#endif // C++20
+#endif // _RANGE_CMP_H