/usr/include/mozjs-38/mozilla/Alignment.h is in libmozjs-38-dev 38.8.0~repack1-0ubuntu4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 | /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* Functionality related to memory alignment. */
#ifndef mozilla_Alignment_h
#define mozilla_Alignment_h
#include <stddef.h>
#include <stdint.h>
namespace mozilla {
/*
* This class, and the corresponding macro MOZ_ALIGNOF, figures out how many
* bytes of alignment a given type needs.
*/
template<typename T>
class AlignmentFinder
{
struct Aligner
{
char mChar;
T mT;
};
public:
static const size_t alignment = sizeof(Aligner) - sizeof(T);
};
#define MOZ_ALIGNOF(T) mozilla::AlignmentFinder<T>::alignment
/*
* Declare the MOZ_ALIGNED_DECL macro for declaring aligned types.
*
* For instance,
*
* MOZ_ALIGNED_DECL(char arr[2], 8);
*
* will declare a two-character array |arr| aligned to 8 bytes.
*/
#if defined(__GNUC__)
# define MOZ_ALIGNED_DECL(_type, _align) \
_type __attribute__((aligned(_align)))
#elif defined(_MSC_VER)
# define MOZ_ALIGNED_DECL(_type, _align) \
__declspec(align(_align)) _type
#else
# warning "We don't know how to align variables on this compiler."
# define MOZ_ALIGNED_DECL(_type, _align) _type
#endif
/*
* AlignedElem<N> is a structure whose alignment is guaranteed to be at least N
* bytes.
*
* We support 1, 2, 4, 8, and 16-bit alignment.
*/
template<size_t Align>
struct AlignedElem;
/*
* We have to specialize this template because GCC doesn't like
* __attribute__((aligned(foo))) where foo is a template parameter.
*/
template<>
struct AlignedElem<1>
{
MOZ_ALIGNED_DECL(uint8_t elem, 1);
};
template<>
struct AlignedElem<2>
{
MOZ_ALIGNED_DECL(uint8_t elem, 2);
};
template<>
struct AlignedElem<4>
{
MOZ_ALIGNED_DECL(uint8_t elem, 4);
};
template<>
struct AlignedElem<8>
{
MOZ_ALIGNED_DECL(uint8_t elem, 8);
};
template<>
struct AlignedElem<16>
{
MOZ_ALIGNED_DECL(uint8_t elem, 16);
};
/*
* This utility pales in comparison to Boost's aligned_storage. The utility
* simply assumes that uint64_t is enough alignment for anyone. This may need
* to be extended one day...
*
* As an important side effect, pulling the storage into this template is
* enough obfuscation to confuse gcc's strict-aliasing analysis into not giving
* false negatives when we cast from the char buffer to whatever type we've
* constructed using the bytes.
*/
template<size_t Nbytes>
struct AlignedStorage
{
union U
{
char mBytes[Nbytes];
uint64_t mDummy;
} u;
const void* addr() const { return u.mBytes; }
void* addr() { return u.mBytes; }
};
template<typename T>
struct AlignedStorage2
{
union U
{
char mBytes[sizeof(T)];
uint64_t mDummy;
} u;
const T* addr() const { return reinterpret_cast<const T*>(u.mBytes); }
T* addr() { return static_cast<T*>(static_cast<void*>(u.mBytes)); }
};
} /* namespace mozilla */
#endif /* mozilla_Alignment_h */
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