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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+/*
+ * Miscellaneous uncategorized functionality.  Please add new functionality to
+ * new headers, or to other appropriate existing headers, not here.
+ */
+
+#ifndef mozilla_Util_h_
+#define mozilla_Util_h_
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Types.h"
+
+#ifdef __cplusplus
+
+namespace mozilla {
+
+/*
+ * This class, and the corresponding macro MOZ_ALIGNOF, figure out how many 
+ * bytes of alignment a given type needs.
+ */
+template<class 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<class 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)); }
+};
+
+/*
+ * Small utility for lazily constructing objects without using dynamic storage.
+ * When a Maybe<T> is constructed, it is |empty()|, i.e., no value of T has
+ * been constructed and no T destructor will be called when the Maybe<T> is
+ * destroyed. Upon calling |construct|, a T object will be constructed with the
+ * given arguments and that object will be destroyed when the owning Maybe<T>
+ * is destroyed.
+ *
+ * N.B. GCC seems to miss some optimizations with Maybe and may generate extra
+ * branches/loads/stores. Use with caution on hot paths.
+ */
+template<class T>
+class Maybe
+{
+    AlignedStorage2<T> storage;
+    bool constructed;
+
+    T& asT() { return *storage.addr(); }
+
+  public:
+    Maybe() { constructed = false; }
+    ~Maybe() { if (constructed) asT().~T(); }
+
+    bool empty() const { return !constructed; }
+
+    void construct() {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T();
+      constructed = true;
+    }
+
+    template<class T1>
+    void construct(const T1& t1) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1);
+      constructed = true;
+    }
+
+    template<class T1, class T2>
+    void construct(const T1& t1, const T2& t2) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3>
+    void construct(const T1& t1, const T2& t2, const T3& t3) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3, class T4>
+    void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3, t4);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3, class T4, class T5>
+    void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3, t4, t5);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3, class T4, class T5,
+             class T6>
+    void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
+                   const T6& t6) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3, class T4, class T5,
+             class T6, class T7>
+    void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
+                   const T6& t6, const T7& t7) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3, class T4, class T5,
+             class T6, class T7, class T8>
+    void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
+                   const T6& t6, const T7& t7, const T8& t8) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3, class T4, class T5,
+             class T6, class T7, class T8, class T9>
+    void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
+                   const T6& t6, const T7& t7, const T8& t8, const T9& t9) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8, t9);
+      constructed = true;
+    }
+
+    template<class T1, class T2, class T3, class T4, class T5,
+             class T6, class T7, class T8, class T9, class T10>
+    void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
+                   const T6& t6, const T7& t7, const T8& t8, const T9& t9, const T10& t10) {
+      MOZ_ASSERT(!constructed);
+      ::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8, t9, t10);
+      constructed = true;
+    }
+
+    T* addr() {
+      MOZ_ASSERT(constructed);
+      return &asT();
+    }
+
+    T& ref() {
+      MOZ_ASSERT(constructed);
+      return asT();
+    }
+
+    const T& ref() const {
+      MOZ_ASSERT(constructed);
+      return const_cast<Maybe*>(this)->asT();
+    }
+
+    void destroy() {
+      ref().~T();
+      constructed = false;
+    }
+
+    void destroyIfConstructed() {
+      if (!empty())
+        destroy();
+    }
+
+  private:
+    Maybe(const Maybe& other) MOZ_DELETE;
+    const Maybe& operator=(const Maybe& other) MOZ_DELETE;
+};
+
+/*
+ * Safely subtract two pointers when it is known that end >= begin.  This avoids
+ * the common compiler bug that if (size_t(end) - size_t(begin)) has the MSB
+ * set, the unsigned subtraction followed by right shift will produce -1, or
+ * size_t(-1), instead of the real difference.
+ */
+template<class T>
+MOZ_ALWAYS_INLINE size_t
+PointerRangeSize(T* begin, T* end)
+{
+  MOZ_ASSERT(end >= begin);
+  return (size_t(end) - size_t(begin)) / sizeof(T);
+}
+
+/*
+ * Compute the length of an array with constant length.  (Use of this method
+ * with a non-array pointer will not compile.)
+ *
+ * Beware of the implicit trailing '\0' when using this with string constants.
+ */
+template<typename T, size_t N>
+MOZ_CONSTEXPR size_t
+ArrayLength(T (&arr)[N])
+{
+  return N;
+}
+
+/*
+ * Compute the address one past the last element of a constant-length array.
+ *
+ * Beware of the implicit trailing '\0' when using this with string constants.
+ */
+template<typename T, size_t N>
+MOZ_CONSTEXPR T*
+ArrayEnd(T (&arr)[N])
+{
+  return arr + ArrayLength(arr);
+}
+
+} /* namespace mozilla */
+
+#endif /* __cplusplus */
+
+/*
+ * MOZ_ARRAY_LENGTH() is an alternative to mozilla::ArrayLength() for C files
+ * that can't use C++ template functions and for MOZ_STATIC_ASSERT() calls that
+ * can't call ArrayLength() when it is not a C++11 constexpr function.
+ */
+#ifdef MOZ_HAVE_CXX11_CONSTEXPR
+#  define MOZ_ARRAY_LENGTH(array)   mozilla::ArrayLength(array)
+#else
+#  define MOZ_ARRAY_LENGTH(array)   (sizeof(array)/sizeof((array)[0]))
+#endif
+
+#endif  /* mozilla_Util_h_ */