--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libstdc++-v3/testsuite/25_algorithms/clamp/constrained.cc	Mon May 25 07:50:57 2020 +0900
@@ -0,0 +1,58 @@
+// 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.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_container;
+using __gnu_test::test_range;
+using __gnu_test::input_iterator_wrapper;
+
+namespace ranges = std::ranges;
+
+struct X
+{
+  int i, j;
+};
+
+void
+test01()
+{
+  VERIFY( ranges::clamp(1, 2, 4) == 2 );
+  VERIFY( ranges::clamp(3, 2, 4) == 3 );
+  VERIFY( ranges::clamp(5, 2, 4) == 4 );
+
+  VERIFY( ranges::clamp(1, 4, 2, ranges::greater{}) == 2 );
+  VERIFY( ranges::clamp(3, 4, 2, ranges::greater{}) == 3 );
+  VERIFY( ranges::clamp(5, 4, 2, ranges::greater{}) == 4 );
+
+  VERIFY( ranges::clamp(1, 2, 4, ranges::greater{}, std::negate<>{}) == 2 );
+  VERIFY( ranges::clamp(3, 2, 4, ranges::greater{}, std::negate<>{}) == 3 );
+  VERIFY( ranges::clamp(5, 2, 4, ranges::greater{}, std::negate<>{}) == 4 );
+
+  static_assert(ranges::clamp(X{1,2}, X{1,3}, X{1,4}, {}, &X::i).j == 2);
+}
+
+int
+main()
+{
+  test01();
+}