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

[Patrick Palka]

https://gcc.gnu.org/g:2d8b80e0af3764d943a37ccefd25295c0c097c17

commit 2d8b80e0af3764d943a37ccefd25295c0c097c17
Author: Patrick Palka <ppalka@gcc.gnu.org>
Date:   Mon Jan 13 13:38:04 2020 -0500

    Add ranges::count

Diff:
---
 libstdc++-v3/include/bits/ranges_algo.h            | 27 ++++++++
 .../testsuite/25_algorithms/count/constrained.cc   | 73 ++++++++++++++++++++++
 2 files changed, 100 insertions(+)

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index 2853849..e9ad648 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -219,6 +219,33 @@ namespace ranges
 				 std::move(__pred), std::move(__proj));
     }
 
+  template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
+	   typename _Tp, typename _Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to,
+				       projected<_Iter, _Proj>,
+				       const _Tp*>
+    constexpr iter_difference_t<_Iter>
+    count(_Iter __first, _Sent __last, const _Tp& __value, _Proj __proj = {})
+    {
+      iter_difference_t<_Iter> __n = 0;
+      for (; __first != __last; ++__first)
+	if (std::__invoke(__proj, *__first) == __value)
+	  ++__n;
+      return __n;
+    }
+
+  template<input_range _Range, typename _Tp, typename _Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to,
+				       projected<iterator_t<_Range>, _Proj>,
+				       const _Tp*>
+    constexpr range_difference_t<_Range>
+    count(_Range&& __r, const _Tp& __value, _Proj __proj = {})
+    {
+      return ranges::count(ranges::begin(__r), ranges::end(__r),
+			   __value, std::move(__proj));
+    }
+
+
 } // namespace ranges
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
diff --git a/libstdc++-v3/testsuite/25_algorithms/count/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/count/constrained.cc
new file mode 100644
index 0000000..18ff693
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/count/constrained.cc
@@ -0,0 +1,73 @@
+// 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;
+using __gnu_test::forward_iterator_wrapper;
+
+namespace ranges = std::ranges;
+
+struct X { int i; };
+
+void
+test01()
+{
+  X x[] = { {2}, {2}, {6}, {8}, {10}, {11}, {2} };
+  auto res = ranges::count(x, x+7, 2, &X::i);
+  VERIFY( res == 3 );
+  res = ranges::count(x, x+7, 8, &X::i);
+  VERIFY( res == 1 );
+  res = ranges::count(x, x+7, 9, &X::i);
+  VERIFY( res == 0 );
+
+  test_container<X, forward_iterator_wrapper> c(x);
+  res = ranges::count(c, 6, &X::i);
+  VERIFY( res == 1 );
+  res = ranges::count(c, 9, &X::i);
+  VERIFY( res == 0 );
+
+  test_range<X, input_iterator_wrapper> r(x);
+  res = ranges::count(r, 2, &X::i);
+  VERIFY( res == 3 );
+  res = ranges::count(r, 9, &X::i);
+  VERIFY( res == 0 );
+}
+
+struct Y { int i; int j; };
+
+void
+test02()
+{
+  static constexpr Y y[] = { {1,2}, {2,4}, {3,6}, {1,6} };
+  static_assert(ranges::count(y, 6, &Y::j) == 2);
+  static_assert(ranges::count(y, 5, &Y::j) == 0);
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}