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

[Patrick Palka]

https://gcc.gnu.org/g:763c92ba57da05ef848eca78206d170102088560

commit 763c92ba57da05ef848eca78206d170102088560
Author: Patrick Palka <ppalka@gcc.gnu.org>
Date:   Mon Jan 13 15:17:25 2020 -0500

    Add ranges::count_if

Diff:
---
 libstdc++-v3/include/bits/ranges_algo.h            | 22 +++++++
 .../25_algorithms/count_if/constrained.cc          | 73 ++++++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index e9ad648..0a78565 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -245,6 +245,28 @@ namespace ranges
 			   __value, std::move(__proj));
     }
 
+  template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
+	   typename _Proj = identity,
+	   indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
+    constexpr iter_difference_t<_Iter>
+    count_if(_Iter __first, _Sent __last, _Pred __pred, _Proj __proj = {})
+    {
+      iter_difference_t<_Iter> __n = 0;
+      for (; __first != __last; ++__first)
+	if (std::__invoke(__pred, std::__invoke(__proj, *__first)))
+	  ++__n;
+      return __n;
+    }
+
+  template<input_range _Range,
+	   typename _Proj = identity,
+	   indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
+    constexpr range_difference_t<_Range>
+    count_if(_Range&& __r, _Pred __pred, _Proj __proj = {})
+    {
+      return ranges::count_if(ranges::begin(__r), ranges::end(__r),
+			      std::move(__pred), std::move(__proj));
+    }
 
 } // namespace ranges
 _GLIBCXX_END_NAMESPACE_VERSION
diff --git a/libstdc++-v3/testsuite/25_algorithms/count_if/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/count_if/constrained.cc
new file mode 100644
index 0000000..79cdae3
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/count_if/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_if(x, x+7, [] (int i) { return i % 2 == 0; }, &X::i);
+  VERIFY( res == 6 );
+  res = ranges::count_if(x, x+7, [] (int i) { return i % 2 == 1; }, &X::i);
+  VERIFY( res == 1 );
+  res = ranges::count_if(x, x+7, [] (int i) { return i < 0; }, &X::i);
+  VERIFY( res == 0 );
+
+  test_container<X, forward_iterator_wrapper> c(x);
+  res = ranges::count_if(c, [] (int i) { return i == 2; }, &X::i);
+  VERIFY( res == 3 );
+  res = ranges::count_if(c, [] (int i) { return i < 0; }, &X::i);
+  VERIFY( res == 0 );
+
+  test_range<X, input_iterator_wrapper> r(x);
+  res = ranges::count_if(c, [] (int i) { return i == 2; }, &X::i);
+  VERIFY( res == 3 );
+  res = ranges::count_if(c, [] (int i) { return i < 0; }, &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_if(y, [] (int i) { return i < 5; }, &Y::j) == 2);
+  static_assert(ranges::count_if(y, [] (int i) { return i != 4; }, &Y::j) == 3);
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}