base/memory/aligned_memory.h

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// AlignedMemory is a POD type that gives you a portable way to specify static
// or local stack data of a given alignment and size. For example, if you need
// static storage for a class, but you want manual control over when the object
// is constructed and destructed (you don't want static initialization and
// destruction), use AlignedMemory:
//
//   static AlignedMemory<sizeof(MyClass), ALIGNOF(MyClass)> my_class;
//
//   // ... at runtime:
//   new(my_class.void_data()) MyClass();
//
//   // ... use it:
//   MyClass* mc = my_class.data_as<MyClass>();
//
//   // ... later, to destruct my_class:
//   my_class.data_as<MyClass>()->MyClass::~MyClass();
//
// Alternatively, a runtime sized aligned allocation can be created:
//
//   float* my_array = static_cast<float*>(AlignedAlloc(size, alignment));
//
//   // ... later, to release the memory:
//   AlignedFree(my_array);
//
// Or using unique_ptr:
//
//   std::unique_ptr<float, AlignedFreeDeleter> my_array(
//       static_cast<float*>(AlignedAlloc(size, alignment)));

#ifndef BASE_MEMORY_ALIGNED_MEMORY_H_
#define BASE_MEMORY_ALIGNED_MEMORY_H_

#include <stddef.h>
#include <stdint.h>

#include "base/base_export.h"
#include "base/compiler_specific.h"

#if defined(COMPILER_MSVC)
#include <malloc.h>
#else
#include <stdlib.h>
#endif

namespace base {

// AlignedMemory is specialized for all supported alignments.
// Make sure we get a compiler error if someone uses an unsupported alignment.
template <size_t Size, size_t ByteAlignment>
struct AlignedMemory {};

#define BASE_DECL_ALIGNED_MEMORY(byte_alignment)                              \
  template <size_t Size>                                                      \
  class AlignedMemory<Size, byte_alignment> {                                 \
   public:                                                                    \
    ALIGNAS(byte_alignment) uint8_t data_[Size];                              \
    void* void_data() { return static_cast<void*>(data_); }                   \
    const void* void_data() const { return static_cast<const void*>(data_); } \
    template <typename Type>                                                  \
    Type* data_as() {                                                         \
      return static_cast<Type*>(void_data());                                 \
    }                                                                         \
    template <typename Type>                                                  \
    const Type* data_as() const {                                             \
      return static_cast<const Type*>(void_data());                           \
    }                                                                         \
                                                                              \
   private:                                                                   \
    void* operator new(size_t);                                               \
    void operator delete(void*);                                              \
  }

// Specialization for all alignments is required because MSVC (as of VS 2008)
// does not understand ALIGNAS(ALIGNOF(Type)) or ALIGNAS(template_param).
// Greater than 4096 alignment is not supported by some compilers, so 4096 is
// the maximum specified here.
BASE_DECL_ALIGNED_MEMORY(1);
BASE_DECL_ALIGNED_MEMORY(2);
BASE_DECL_ALIGNED_MEMORY(4);
BASE_DECL_ALIGNED_MEMORY(8);
BASE_DECL_ALIGNED_MEMORY(16);
BASE_DECL_ALIGNED_MEMORY(32);
BASE_DECL_ALIGNED_MEMORY(64);
BASE_DECL_ALIGNED_MEMORY(128);
BASE_DECL_ALIGNED_MEMORY(256);
BASE_DECL_ALIGNED_MEMORY(512);
BASE_DECL_ALIGNED_MEMORY(1024);
BASE_DECL_ALIGNED_MEMORY(2048);
BASE_DECL_ALIGNED_MEMORY(4096);

#undef BASE_DECL_ALIGNED_MEMORY

BASE_EXPORT void* AlignedAlloc(size_t size, size_t alignment);

inline void AlignedFree(void* ptr) {
#if defined(COMPILER_MSVC)
  _aligned_free(ptr);
#else
  free(ptr);
#endif
}

// Deleter for use with unique_ptr. E.g., use as
//   std::unique_ptr<Foo, base::AlignedFreeDeleter> foo;
struct AlignedFreeDeleter {
  inline void operator()(void* ptr) const {
    AlignedFree(ptr);
  }
};

}  // namespace base

#endif  // BASE_MEMORY_ALIGNED_MEMORY_H_