src/butil/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 scoped_ptr:
//
//   scoped_ptr<float, AlignedFreeDeleter> my_array(
//       static_cast<float*>(AlignedAlloc(size, alignment)));

#ifndef BUTIL_MEMORY_ALIGNED_MEMORY_H_
#define BUTIL_MEMORY_ALIGNED_MEMORY_H_

#include "butil/base_export.h"
#include "butil/basictypes.h"
#include "butil/compiler_specific.h"

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

namespace butil {

// 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 {};

// std::aligned_storage has been deprecated in C++23,
// because aligned_* are harmful to codebases and should not be used.
// For details, see https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p1413r3.pdf
#if __cplusplus >= 201103L
// In most places, use the C++11 keyword "alignas", which is preferred.
#define DECL_ALIGNED_BUFFER(buffer_name, byte_alignment, size) \
    alignas(byte_alignment) uint8_t buffer_name[size]
#else
#define DECL_ALIGNED_BUFFER(buffer_name, byte_alignment, size) \
    ALIGNAS(byte_alignment) uint8_t buffer_name[size]
#endif

#define BUTIL_DECL_ALIGNED_MEMORY(byte_alignment)                 \
    template <size_t Size>                                        \
    class AlignedMemory<Size, byte_alignment> {                   \
     public:                                                      \
      DECL_ALIGNED_BUFFER(data_, byte_alignment, 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.
BUTIL_DECL_ALIGNED_MEMORY(1);
BUTIL_DECL_ALIGNED_MEMORY(2);
BUTIL_DECL_ALIGNED_MEMORY(4);
BUTIL_DECL_ALIGNED_MEMORY(8);
BUTIL_DECL_ALIGNED_MEMORY(16);
BUTIL_DECL_ALIGNED_MEMORY(32);
BUTIL_DECL_ALIGNED_MEMORY(64);
BUTIL_DECL_ALIGNED_MEMORY(128);
BUTIL_DECL_ALIGNED_MEMORY(256);
BUTIL_DECL_ALIGNED_MEMORY(512);
BUTIL_DECL_ALIGNED_MEMORY(1024);
BUTIL_DECL_ALIGNED_MEMORY(2048);
BUTIL_DECL_ALIGNED_MEMORY(4096);

#undef BUTIL_DECL_ALIGNED_MEMORY

BUTIL_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 scoped_ptr. E.g., use as
//   scoped_ptr<Foo, butil::AlignedFreeDeleter> foo;
struct AlignedFreeDeleter {
  inline void operator()(void* ptr) const {
    AlignedFree(ptr);
  }
};

}  // namespace butil

#endif  // BUTIL_MEMORY_ALIGNED_MEMORY_H_