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

[Patrick Palka]

https://gcc.gnu.org/g:e9d0c93beb62909d18038f5109d986868ff9aedd

commit e9d0c93beb62909d18038f5109d986868ff9aedd
Author: Patrick Palka <ppalka@gcc.gnu.org>
Date:   Fri Jan 17 12:37:48 2020 -0500

    Add ranges::adjacent_find

Diff:
---
 libstdc++-v3/include/bits/ranges_algo.h            | 33 +++++++++++
 .../25_algorithms/adjacent_find/constrained.cc     | 68 ++++++++++++++++++++++
 2 files changed, 101 insertions(+)

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index b89f19a..0c53a54 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -500,6 +500,39 @@ namespace ranges
 			      std::move(__proj1), std::move(__proj2));
     }
 
+    template<forward_iterator _Iter, sentinel_for<_Iter> _Sent,
+	     class _Proj = identity,
+	     indirect_binary_predicate<projected<_Iter, _Proj>,
+				       projected<_Iter, _Proj>> _Pred
+	       = ranges::equal_to>
+      constexpr _Iter
+      adjacent_find(_Iter __first, _Sent __last,
+		    _Pred __pred = {}, _Proj __proj = {})
+      {
+	if (__first == __last)
+	  return __last;
+	auto __next = __first;
+	while (++__next != __last)
+	  {
+	    if (std::__invoke(__pred,
+			      std::__invoke(__proj, *__first),
+			      std::__invoke(__proj, *__next)))
+	      return __first;
+	    __first = __next;
+	  }
+	return __last;
+      }
+
+    template<forward_range _Range, class _Proj = identity,
+	     indirect_binary_predicate<
+	       projected<iterator_t<_Range>, _Proj>,
+	       projected<iterator_t<_Range>, _Proj>> _Pred = ranges::equal_to>
+      constexpr safe_iterator_t<_Range>
+      adjacent_find(_Range&& __r, _Pred __pred = {}, _Proj __proj = {})
+      {
+	return ranges::adjacent_find(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/adjacent_find/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/adjacent_find/constrained.cc
new file mode 100644
index 0000000..d56ac5a
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/adjacent_find/constrained.cc
@@ -0,0 +1,68 @@
+// 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} };
+  int y[] = { 2, 7, 8, 8, 9 };
+
+  VERIFY( ranges::adjacent_find(x, x+6, {}, &X::i) == x+0 );
+  VERIFY( ranges::adjacent_find(x+1, x+6, {}, &X::i) == x+6 );
+  VERIFY( ranges::adjacent_find(y) == y+2 );
+  VERIFY( ranges::adjacent_find(y, y+4) == y+2 );
+
+  test_container<X, forward_iterator_wrapper> c(x);
+  VERIFY( ranges::adjacent_find(c, {}, &X::i) == ranges::begin(c) );
+
+  test_range<int, forward_iterator_wrapper> r(y);
+  auto res = ranges::adjacent_find(r);
+  VERIFY( *res == 8 && *++res == 8 );
+}
+
+void
+test02()
+{
+  static constexpr X x[] = { {2}, {2}, {6}, {8}, {10}, {11} };
+  static constexpr X y[] = { {2}, {6}, {8}, {10}, {11} };
+  static_assert(ranges::adjacent_find(x, {}, &X::i) == x+0);
+  static_assert(ranges::adjacent_find(y, {}, &X::i) == y+5);
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}
+