[gcc(refs/users/ppalka/heads/libstdcxx-constrained-algos)] Add ranges::reverse_copy

[Patrick Palka]

https://gcc.gnu.org/g:0c78fdb6ff67edcc8122d51dad825091a2b47254

commit 0c78fdb6ff67edcc8122d51dad825091a2b47254
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Jan 22 12:30:50 2020 -0500

    Add ranges::reverse_copy

Diff:
---
 libstdc++-v3/include/bits/ranges_algo.h            | 29 +++++++++
 .../25_algorithms/reverse_copy/constrained.cc      | 74 ++++++++++++++++++++++
 2 files changed, 103 insertions(+)

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index e0c13c3..3fa945d 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -1565,6 +1565,35 @@ namespace ranges
       return ranges::reverse(ranges::begin(__r), ranges::end(__r));
     }
 
+  template<typename _Iter, typename _Out>
+  using reverse_copy_result = copy_result<_Iter, _Out>;
+
+  template<bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
+	   weakly_incrementable _Out>
+    requires indirectly_copyable<_Iter, _Out>
+    constexpr reverse_copy_result<_Iter, _Out>
+    reverse_copy(_Iter __first, _Sent __last, _Out __result)
+    {
+      auto __i = ranges::next(__first, __last);
+      auto __tail = __i;
+      while (__first != __tail)
+	{
+	  --__tail;
+	  *__result = *__tail;
+	  ++__result;
+	}
+      return {__i, __result};
+    }
+
+  template<bidirectional_range _Range, weakly_incrementable _Out>
+    requires indirectly_copyable<iterator_t<_Range>, _Out>
+    constexpr reverse_copy_result<safe_iterator_t<_Range>, _Out>
+    reverse_copy(_Range&& __r, _Out __result)
+    {
+      return ranges::reverse_copy(ranges::begin(__r), ranges::end(__r),
+				  std::move(__result));
+    }
+
 } // namespace ranges
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
diff --git a/libstdc++-v3/testsuite/25_algorithms/reverse_copy/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/reverse_copy/constrained.cc
new file mode 100644
index 0000000..1ee40be
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/reverse_copy/constrained.cc
@@ -0,0 +1,74 @@
+// 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_range;
+using __gnu_test::test_container;
+using __gnu_test::bidirectional_iterator_wrapper;
+
+namespace ranges = std::ranges;
+
+void
+test01()
+{
+  int x[] = { 1, 2, 3, 4 };
+  int w[4];
+  test_container<int, bidirectional_iterator_wrapper> cx(x), cw(w);
+  const int y[] = { 4, 3, 2, 1 };
+
+  auto [in,out] = ranges::reverse_copy(cx, cw.begin());
+  VERIFY( in == ranges::end(cx) && out == cw.end() );
+  VERIFY( ranges::equal(cw, y) );
+}
+
+void
+test02()
+{
+  int x[] = { 1, 2, 3, 4, 5 };
+  int w[5];
+  test_range<int, bidirectional_iterator_wrapper> rx(x), rw(w);
+  const int y[] = { 5, 4, 3, 2, 1 };
+
+  auto [in,out] = ranges::reverse_copy(rx, ranges::begin(rw));
+  VERIFY( in == ranges::end(rx) && out == ranges::end(rw) );
+  VERIFY( ranges::equal(rw, y) );
+}
+
+constexpr bool
+test03()
+{
+  const int x[] = { 1, 2, 3 };
+  int w[2];
+  const int y[] = { 2, 1 };
+  ranges::reverse_copy(x, x+2, w);
+  return ranges::equal(w, y);
+}
+
+int
+main()
+{
+  test01();
+  test02();
+
+  static_assert(test03());
+}