re PR libstdc++/57350 (std::align missing)

	PR libstdc++/57350
	* include/std/memory (align): Do not adjust correctly aligned address.
	* testsuite/20_util/align/2.cc: New.

From-SVN: r216149

libstdc++-v3/ChangeLog

+2014-10-13  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/57350
+	* include/std/memory (align): Do not adjust correctly aligned address.
+	* testsuite/20_util/align/2.cc: New.
+
 2014-10-13  Siva Chandra Reddy  <sivachandra@google.com>
 
 	* python/libstdcxx/v6/xmethods.py: Add xmethods for std::array,

libstdc++-v3/include/std/memory

@@ -113,14 +113,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 inline void*
 align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
 {
-  const size_t __diff = __align - reinterpret_cast<uintptr_t>(__ptr) % __align;
-  if (__diff + __size >= __space)
+  const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
+  const auto __aligned = (__intptr - 1u + __align) & -__align;
+  const auto __diff = __aligned - __intptr;
+  if ((__size + __diff) > __space)
     return nullptr;
   else
     {
       __space -= __diff;
-      __ptr = static_cast<char*>(__ptr) + __diff;
-      return __ptr;
+      return __ptr = reinterpret_cast<void*>(__aligned);
     }
 }
 

libstdc++-v3/testsuite/20_util/align/2.cc

+// { dg-options " -std=gnu++11 " }
+
+// Copyright (C) 2014 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/>.
+
+// C++11 [ptr.align] (20.6.5): std::align
+
+#include <memory>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  bool test __attribute__((unused)) = true;
+
+  int i = 0;
+  void* ptr = &i;
+  auto space = sizeof(i);
+  auto p2 = std::align(alignof(i), space, ptr, space);
+  VERIFY( ptr == &i );
+  VERIFY( p2 == &i );
+  VERIFY(space == sizeof(i));
+}
+
+int main()
+{
+  test01();
+}