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       1             : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
       2             : /* vim: set ts=8 sts=2 et sw=2 tw=80: */
       3             : /* This Source Code Form is subject to the terms of the Mozilla Public
       4             :  * License, v. 2.0. If a copy of the MPL was not distributed with this
       5             :  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
       6             : 
       7             : /* Functionality related to memory alignment. */
       8             : 
       9             : #ifndef mozilla_Alignment_h
      10             : #define mozilla_Alignment_h
      11             : 
      12             : #include "mozilla/Attributes.h"
      13             : #include <stddef.h>
      14             : #include <stdint.h>
      15             : 
      16             : namespace mozilla {
      17             : 
      18             : /*
      19             :  * This class, and the corresponding macro MOZ_ALIGNOF, figures out how many
      20             :  * bytes of alignment a given type needs.
      21             :  */
      22             : template<typename T>
      23             : class AlignmentFinder
      24             : {
      25             :   struct Aligner
      26             :   {
      27             :     char mChar;
      28             :     T mT;
      29             :   };
      30             : 
      31             : public:
      32             :   static const size_t alignment = sizeof(Aligner) - sizeof(T);
      33             : };
      34             : 
      35             : #define MOZ_ALIGNOF(T) mozilla::AlignmentFinder<T>::alignment
      36             : 
      37             : /*
      38             :  * Declare the MOZ_ALIGNED_DECL macro for declaring aligned types.
      39             :  *
      40             :  * For instance,
      41             :  *
      42             :  *   MOZ_ALIGNED_DECL(char arr[2], 8);
      43             :  *
      44             :  * will declare a two-character array |arr| aligned to 8 bytes.
      45             :  */
      46             : 
      47             : #if defined(__GNUC__)
      48             : #  define MOZ_ALIGNED_DECL(_type, _align) \
      49             :      _type __attribute__((aligned(_align)))
      50             : #elif defined(_MSC_VER)
      51             : #  define MOZ_ALIGNED_DECL(_type, _align) \
      52             :      __declspec(align(_align)) _type
      53             : #else
      54             : #  warning "We don't know how to align variables on this compiler."
      55             : #  define MOZ_ALIGNED_DECL(_type, _align) _type
      56             : #endif
      57             : 
      58             : /*
      59             :  * AlignedElem<N> is a structure whose alignment is guaranteed to be at least N
      60             :  * bytes.
      61             :  *
      62             :  * We support 1, 2, 4, 8, and 16-bit alignment.
      63             :  */
      64             : template<size_t Align>
      65             : struct AlignedElem;
      66             : 
      67             : /*
      68             :  * We have to specialize this template because GCC doesn't like
      69             :  * __attribute__((aligned(foo))) where foo is a template parameter.
      70             :  */
      71             : 
      72             : template<>
      73             : struct AlignedElem<1>
      74             : {
      75             :   MOZ_ALIGNED_DECL(uint8_t elem, 1);
      76             : };
      77             : 
      78             : template<>
      79             : struct AlignedElem<2>
      80             : {
      81             :   MOZ_ALIGNED_DECL(uint8_t elem, 2);
      82             : };
      83             : 
      84             : template<>
      85             : struct AlignedElem<4>
      86             : {
      87             :   MOZ_ALIGNED_DECL(uint8_t elem, 4);
      88             : };
      89             : 
      90             : template<>
      91             : struct AlignedElem<8>
      92             : {
      93             :   MOZ_ALIGNED_DECL(uint8_t elem, 8);
      94             : };
      95             : 
      96             : template<>
      97             : struct AlignedElem<16>
      98             : {
      99             :   MOZ_ALIGNED_DECL(uint8_t elem, 16);
     100             : };
     101             : 
     102             : template<typename T>
     103             : struct MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS AlignedStorage2
     104             : {
     105             :   union U
     106             :   {
     107             :     char mBytes[sizeof(T)];
     108             :     uint64_t mDummy;
     109             :   } u;
     110             : 
     111      126954 :   const T* addr() const { return reinterpret_cast<const T*>(u.mBytes); }
     112     7863325 :   T* addr() { return static_cast<T*>(static_cast<void*>(u.mBytes)); }
     113             : 
     114         141 :   AlignedStorage2() = default;
     115             : 
     116             :   // AlignedStorage2 is non-copyable: the default copy constructor violates
     117             :   // strict aliasing rules, per bug 1269319.
     118             :   AlignedStorage2(const AlignedStorage2&) = delete;
     119             :   void operator=(const AlignedStorage2&) = delete;
     120             : };
     121             : 
     122             : } /* namespace mozilla */
     123             : 
     124             : #endif /* mozilla_Alignment_h */