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[v3 PATCH] PR libstdc++/87619


Simple, short, and sweet, just a thinko.

2018-10-16  Ville Voutilainen  <ville.voutilainen@gmail.com>

    PR libstdc++/87619
    * include/std/variant (__select_index): Fix an off-by-one.
    * testsuite/20_util/variant/87619.cc: New.
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 2d86a70..55b6440 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -362,7 +362,7 @@ namespace __variant
 
   template <typename... _Types>
   using __select_index =
-    typename __select_int::_Select_int_base<sizeof...(_Types) + 1,
+    typename __select_int::_Select_int_base<sizeof...(_Types),
 					    unsigned char,
 					    unsigned short>::type::value_type;
 
diff --git a/libstdc++-v3/testsuite/20_util/variant/87619.cc b/libstdc++-v3/testsuite/20_util/variant/87619.cc
new file mode 100644
index 0000000..a8db6b8
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/variant/87619.cc
@@ -0,0 +1,46 @@
+// Copyright (C) 2018 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++17" }
+// { dg-do compile { target c++17 } }
+
+#include <variant>
+#include <utility>
+
+
+template<std::size_t I>
+struct S {
+};
+
+template <std::size_t... Is>
+void f_impl(std::index_sequence<Is...>)
+{
+	using V = std::variant<S<Is>...>;
+	static_assert(sizeof(V) == 2);
+}
+
+template <std::size_t I>
+void f()
+{
+	f_impl(std::make_index_sequence<I>{});
+}
+
+int main()
+{
+	f<254>();
+	f<255>();
+}

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