base/memory/aligned_memory.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // AlignedMemory is a POD type that gives you a portable way to specify static
   6 // or local stack data of a given alignment and size. For example, if you need
   7 // static storage for a class, but you want manual control over when the object
   8 // is constructed and destructed (you don't want static initialization and
   9 // destruction), use AlignedMemory:
  10 //
  11 //   static AlignedMemory<sizeof(MyClass), ALIGNOF(MyClass)> my_class;
  12 //
  13 //   // ... at runtime:
  14 //   new(my_class.void_data()) MyClass();
  15 //
  16 //   // ... use it:
  17 //   MyClass* mc = my_class.data_as<MyClass>();
  18 //
  19 //   // ... later, to destruct my_class:
  20 //   my_class.data_as<MyClass>()->MyClass::~MyClass();
  21 //
  22 // Alternatively, a runtime sized aligned allocation can be created:
  23 //
  24 //   float* my_array = static_cast<float*>(AlignedAlloc(size, alignment));
  25 //
  26 //   // ... later, to release the memory:
  27 //   AlignedFree(my_array);
  28 //
  29 // Or using scoped_ptr:
  30 //
  31 //   scoped_ptr<float, AlignedFreeDeleter> my_array(
  32 //       static_cast<float*>(AlignedAlloc(size, alignment)));
  33
  34 #ifndef BASE_MEMORY_ALIGNED_MEMORY_H_
  35 #define BASE_MEMORY_ALIGNED_MEMORY_H_
  36
  37 #include "base/base_export.h"
  38 #include "base/basictypes.h"
  39 #include "base/compiler_specific.h"
  40
  41 #if defined(COMPILER_MSVC)
  42 #include <malloc.h>
  43 #else
  44 #include <stdlib.h>
  45 #endif
  46
  47 namespace base {
  48
  49 // AlignedMemory is specialized for all supported alignments.
  50 // Make sure we get a compiler error if someone uses an unsupported alignment.
  51 template <size_t Size, size_t ByteAlignment>
  52 struct AlignedMemory {};
  53
  54 #define BASE_DECL_ALIGNED_MEMORY(byte_alignment) \
  55     template <size_t Size> \
  56     class AlignedMemory<Size, byte_alignment> { \
  57      public: \
  58       ALIGNAS(byte_alignment) uint8 data_[Size]; \
  59       void* void_data() { return static_cast<void*>(data_); } \
  60       const void* void_data() const { \
  61         return static_cast<const void*>(data_); \
  62       } \
  63       template<typename Type> \
  64       Type* data_as() { return static_cast<Type*>(void_data()); } \
  65       template<typename Type> \
  66       const Type* data_as() const { \
  67         return static_cast<const Type*>(void_data()); \
  68       } \
  69      private: \
  70       void* operator new(size_t); \
  71       void operator delete(void*); \
  72     }
  73
  74 // Specialization for all alignments is required because MSVC (as of VS 2008)
  75 // does not understand ALIGNAS(ALIGNOF(Type)) or ALIGNAS(template_param).
  76 // Greater than 4096 alignment is not supported by some compilers, so 4096 is
  77 // the maximum specified here.
  78 BASE_DECL_ALIGNED_MEMORY(1);
  79 BASE_DECL_ALIGNED_MEMORY(2);
  80 BASE_DECL_ALIGNED_MEMORY(4);
  81 BASE_DECL_ALIGNED_MEMORY(8);
  82 BASE_DECL_ALIGNED_MEMORY(16);
  83 BASE_DECL_ALIGNED_MEMORY(32);
  84 BASE_DECL_ALIGNED_MEMORY(64);
  85 BASE_DECL_ALIGNED_MEMORY(128);
  86 BASE_DECL_ALIGNED_MEMORY(256);
  87 BASE_DECL_ALIGNED_MEMORY(512);
  88 BASE_DECL_ALIGNED_MEMORY(1024);
  89 BASE_DECL_ALIGNED_MEMORY(2048);
  90 BASE_DECL_ALIGNED_MEMORY(4096);
  91
  92 #undef BASE_DECL_ALIGNED_MEMORY
  93
  94 BASE_EXPORT void* AlignedAlloc(size_t size, size_t alignment);
  95
  96 inline void AlignedFree(void* ptr) {
  97 #if defined(COMPILER_MSVC)
  98   _aligned_free(ptr);
  99 #else
 100   free(ptr);
 101 #endif
 102 }
 103
 104 // Deleter for use with scoped_ptr. E.g., use as
 105 //   scoped_ptr<Foo, base::AlignedFreeDeleter> foo;
 106 struct AlignedFreeDeleter {
 107   inline void operator()(void* ptr) const {
 108     AlignedFree(ptr);
 109   }
 110 };
 111
 112 }  // namespace base
 113
 114 #endif  // BASE_MEMORY_ALIGNED_MEMORY_H_