1 files changed, 188 insertions, 0 deletions
diff --git a/mfbt/ArrayUtils.h b/mfbt/ArrayUtils.h
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+++ b/mfbt/ArrayUtils.h
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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/. */
+
+/*
+ * 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>
+#include <stdint.h>
+
+#ifdef __cplusplus
+#  include <algorithm>
+#  include <type_traits>
+
+#  include "mozilla/Alignment.h"
+
+namespace mozilla {
+
+template <typename T, size_t Length>
+class Array;
+template <typename IndexType, IndexType SizeAsEnumValue, typename ValueType>
+class EnumeratedArray;
+
+/*
+ * Safely subtract two pointers when it is known that aEnd >= aBegin, yielding a
+ * size_t result.
+ *
+ * Ordinary pointer subtraction yields a ptrdiff_t result, which, being signed,
+ * has insufficient range to express the distance between pointers at opposite
+ * ends of the address space. Furthermore, most compilers use ptrdiff_t to
+ * represent the intermediate byte address distance, before dividing by
+ * sizeof(T); if that intermediate result overflows, they'll produce results
+ * with the wrong sign even when the correct scaled distance would fit in a
+ * ptrdiff_t.
+ */
+template <class T>
+MOZ_ALWAYS_INLINE size_t PointerRangeSize(T* aBegin, T* aEnd) {
+  MOZ_ASSERT(aEnd >= aBegin);
+  return (size_t(aEnd) - size_t(aBegin)) / 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>
+constexpr size_t ArrayLength(T (&aArr)[N]) {
+  return N;
+}
+
+template <typename T, size_t N>
+constexpr size_t ArrayLength(const Array<T, N>& aArr) {
+  return N;
+}
+
+template <typename E, E N, typename T>
+constexpr size_t ArrayLength(const EnumeratedArray<E, N, T>& aArr) {
+  return size_t(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>
+constexpr T* ArrayEnd(T (&aArr)[N]) {
+  return aArr + ArrayLength(aArr);
+}
+
+template <typename T, size_t N>
+constexpr T* ArrayEnd(Array<T, N>& aArr) {
+  return &aArr[0] + ArrayLength(aArr);
+}
+
+template <typename T, size_t N>
+constexpr const T* ArrayEnd(const Array<T, N>& aArr) {
+  return &aArr[0] + ArrayLength(aArr);
+}
+
+/**
+ * std::equal has subpar ergonomics.
+ */
+
+template <typename T, typename U, size_t N>
+bool ArrayEqual(const T (&a)[N], const U (&b)[N]) {
+  return std::equal(a, a + N, b);
+}
+
+template <typename T, typename U>
+bool ArrayEqual(const T* const a, const U* const b, const size_t n) {
+  return std::equal(a, a + n, b);
+}
+
+namespace detail {
+
+template <typename AlignType, typename Pointee, typename = void>
+struct AlignedChecker {
+  static void test(const Pointee* aPtr) {
+    MOZ_ASSERT((uintptr_t(aPtr) % MOZ_ALIGNOF(AlignType)) == 0,
+               "performing a range-check with a misaligned pointer");
+  }
+};
+
+template <typename AlignType, typename Pointee>
+struct AlignedChecker<AlignType, Pointee,
+                      std::enable_if_t<std::is_void_v<AlignType>>> {
+  static void test(const Pointee* aPtr) {}
+};
+
+}  // namespace detail
+
+/**
+ * Determines whether |aPtr| points at an object in the range [aBegin, aEnd).
+ *
+ * |aPtr| must have the same alignment as |aBegin| and |aEnd|.  This usually
+ * should be achieved by ensuring |aPtr| points at a |U|, not just that it
+ * points at a |T|.
+ *
+ * It is a usage error for any argument to be misaligned.
+ *
+ * It's okay for T* to be void*, and if so U* may also be void*.  In the latter
+ * case no argument is required to be aligned (obviously, as void* implies no
+ * particular alignment).
+ */
+template <typename T, typename U>
+inline std::enable_if_t<std::is_same_v<T, U> || std::is_base_of<T, U>::value ||
+                            std::is_void_v<T>,
+                        bool>
+IsInRange(const T* aPtr, const U* aBegin, const U* aEnd) {
+  MOZ_ASSERT(aBegin <= aEnd);
+  detail::AlignedChecker<U, T>::test(aPtr);
+  detail::AlignedChecker<U, U>::test(aBegin);
+  detail::AlignedChecker<U, U>::test(aEnd);
+  return aBegin <= reinterpret_cast<const U*>(aPtr) &&
+         reinterpret_cast<const U*>(aPtr) < aEnd;
+}
+
+/**
+ * Convenience version of the above method when the valid range is specified as
+ * uintptr_t values.  As above, |aPtr| must be aligned, and |aBegin| and |aEnd|
+ * must be aligned with respect to |T|.
+ */
+template <typename T>
+inline bool IsInRange(const T* aPtr, uintptr_t aBegin, uintptr_t aEnd) {
+  return IsInRange(aPtr, reinterpret_cast<const T*>(aBegin),
+                   reinterpret_cast<const T*>(aEnd));
+}
+
+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 */