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+/* -*- 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 "mozilla/Attributes.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; }
+
+ AlignedStorage() = default;
+
+ // AlignedStorage is non-copyable: the default copy constructor violates
+ // strict aliasing rules, per bug 1269319.
+ AlignedStorage(const AlignedStorage&) = delete;
+ void operator=(const AlignedStorage&) = delete;
+};
+
+template<typename T>
+struct MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS 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)); }
+
+ AlignedStorage2() = default;
+
+ // AlignedStorage2 is non-copyable: the default copy constructor violates
+ // strict aliasing rules, per bug 1269319.
+ AlignedStorage2(const AlignedStorage2&) = delete;
+ void operator=(const AlignedStorage2&) = delete;
+};
+
+} /* namespace mozilla */
+
+#endif /* mozilla_Alignment_h */