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Re: [PATCH 1/2] libstdc++: Add std::align.


On 16/04/14 17:06 +0200, Rüdiger Sonderfeld wrote:
C++11 [ptr.align].

This should probably not be inline.  But for now this avoids any ABI
changes.

* libstdc++-v3/testsuite/20_util/align/1.cc: New file.
* libstdc++-v3/include/std/memory (align): New function.

Fixed (the new function should be in namespace std!) and applied to
trunk. Thanks for the patch.

Tested x86_64-linux.
commit d49cd05620599277845f89325ac8a43622650e8f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Oct 13 10:50:16 2014 +0100

    2014-10-13  R??diger Sonderfeld  <ruediger@c-plusplus.de>
    
    	* include/std/memory (align): Define.
    	* testsuite/20_util/align/1.cc: New.

diff --git a/libstdc++-v3/include/std/memory b/libstdc++-v3/include/std/memory
index dafec0c..affc8b1 100644
--- a/libstdc++-v3/include/std/memory
+++ b/libstdc++-v3/include/std/memory
@@ -87,4 +87,46 @@
 #  include <backward/auto_ptr.h>
 #endif
 
+#if __cplusplus >= 201103L
+#  include <cstdint>
+#  ifdef _GLIBCXX_USE_C99_STDINT_TR1
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+/**
+ *  @brief Fit aligned storage in buffer.
+ *
+ *  [ptr.align]
+ *
+ *  This function tries to fit @a __size bytes of storage with alignment
+ *  @a __align into the buffer @a __ptr of size @a __space bytes.  If such
+ *  a buffer fits then @a __ptr is changed to point to the first byte of the
+ *  aligned storage and @a __space is reduced by the bytes used for alignment.
+ *
+ *  @param __align   A fundamental or extended alignment value.
+ *  @param __size    Size of the aligned storage required.
+ *  @param __ptr     Pointer to a buffer of @a __space bytes.
+ *  @param __space   Size of the buffer pointed to by @a __ptr.
+ *  @return the updated pointer if the aligned storage fits, otherwise nullptr.
+ */
+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)
+    return nullptr;
+  else
+    {
+      __space -= __diff;
+      __ptr = static_cast<char*>(__ptr) + __diff;
+      return __ptr;
+    }
+}
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace
+#endif // _GLIBCXX_USE_C99_STDINT_TR1
+#endif // C++11
+
 #endif /* _GLIBCXX_MEMORY */
diff --git a/libstdc++-v3/testsuite/20_util/align/1.cc b/libstdc++-v3/testsuite/20_util/align/1.cc
new file mode 100644
index 0000000..d1f94e9
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/align/1.cc
@@ -0,0 +1,61 @@
+// { dg-options " -std=gnu++11 " }
+
+// 2014-04-16 R??diger Sonderfeld  <ruediger@c-plusplus.de>
+
+// 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 <cstdint>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  bool test __attribute__((unused)) = true;
+
+  size_t space = 100;
+  void* ptr = new char[space];
+  char* const orig_ptr = static_cast<char*>(ptr);
+  char* old_ptr = orig_ptr;
+  const size_t orig_space = space;
+  size_t old_space = space;
+  const size_t alignment = 16;
+  const size_t size = 10;
+  while( void* const r = std::align(alignment, size, ptr, space) )
+    {
+      VERIFY( r == ptr );
+      uintptr_t p = reinterpret_cast<uintptr_t>(ptr);
+      VERIFY( p % alignment == 0 );
+      char* const x = static_cast<char*>(ptr);
+      VERIFY( x - old_ptr == old_space - space );
+      VERIFY( (void*)x < (void*)(orig_ptr + orig_space) );
+      VERIFY( (void*)(x + size) < (void*)(orig_ptr + orig_space) );
+      ptr = x + size;
+      old_ptr = x;
+      old_space = space;
+      space -= size;
+    }
+  delete [] orig_ptr;
+}
+
+int main()
+{
+  test01();
+}

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