diff -r 000000000000 -r 6474c204b198 mfbt/Alignment.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mfbt/Alignment.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,137 @@
+/* -*- 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 c;
+        T t;
+    };
+
+  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 bytes[Nbytes];
+      uint64_t _;
+    } u;
+
+    const void* addr() const { return u.bytes; }
+    void* addr() { return u.bytes; }
+};
+
+template<typename T>
+struct AlignedStorage2
+{
+    union U {
+      char bytes[sizeof(T)];
+      uint64_t _;
+    } u;
+
+    const T* addr() const { return reinterpret_cast<const T*>(u.bytes); }
+    T* addr() { return static_cast<T*>(static_cast<void*>(u.bytes)); }
+};
+
+} /* namespace mozilla */
+
+#endif /* mozilla_Alignment_h */