diff -r 000000000000 -r 6474c204b198 mfbt/ArrayUtils.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mfbt/ArrayUtils.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,111 @@
+/* -*- 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/. */
+
+/*
+ * Implements various helper functions related to arrays.
+ */
+
+#ifndef mozilla_ArrayUtils_h
+#define mozilla_ArrayUtils_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+
+#include "mozilla/Array.h"
+
+namespace mozilla {
+
+/*
+ * 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;
+}
+
+template<typename T, size_t N>
+MOZ_CONSTEXPR size_t
+ArrayLength(const Array<T, N>& arr)
+{
+  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);
+}
+
+template<typename T, size_t N>
+MOZ_CONSTEXPR T*
+ArrayEnd(Array<T, N>& arr)
+{
+  return &arr[0] + ArrayLength(arr);
+}
+
+template<typename T, size_t N>
+MOZ_CONSTEXPR const T*
+ArrayEnd(const Array<T, N>& arr)
+{
+  return &arr[0] + ArrayLength(arr);
+}
+
+namespace detail {
+
+/*
+ * Helper for the MOZ_ARRAY_LENGTH() macro to make the length a typesafe
+ * compile-time constant even on compilers lacking constexpr support.
+ */
+template <typename T, size_t N>
+char (&ArrayLengthHelper(T (&array)[N]))[N];
+
+} /* namespace detail */
+
+} /* 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 static_assert() calls that
+ * can't call ArrayLength() when it is not a C++11 constexpr function.
+ */
+#ifdef __cplusplus
+#  define MOZ_ARRAY_LENGTH(array)   sizeof(mozilla::detail::ArrayLengthHelper(array))
+#else
+#  define MOZ_ARRAY_LENGTH(array)   (sizeof(array)/sizeof((array)[0]))
+#endif
+
+#endif /* mozilla_ArrayUtils_h */