1 files changed, 82 insertions, 0 deletions
diff --git a/mfbt/Range.h b/mfbt/Range.h
new file mode 100644
index 0000000000..35cd4a0e07
--- /dev/null
+++ b/mfbt/Range.h
@@ -0,0 +1,82 @@
+/* -*- 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/. */
+
+#ifndef mozilla_Range_h
+#define mozilla_Range_h
+
+#include "mozilla/RangedPtr.h"
+#include "mozilla/Span.h"
+
+#include <stddef.h>
+#include <type_traits>
+
+namespace mozilla {
+
+// Range<T> is a tuple containing a pointer and a length.
+template <typename T>
+class Range {
+  template <typename U>
+  friend class Range;
+
+  // Reassignment of RangedPtrs is so (subtly) restrictive that we just make
+  // Range immutable.
+  const RangedPtr<T> mStart;
+  const RangedPtr<T> mEnd;
+
+ public:
+  Range() : mStart(nullptr, 0), mEnd(nullptr, 0) {}
+  Range(T* aPtr, size_t aLength)
+      : mStart(aPtr, aPtr, aPtr + aLength),
+        mEnd(aPtr + aLength, aPtr, aPtr + aLength) {
+    if (!aPtr) {
+      MOZ_ASSERT_DEBUG_OR_FUZZING(
+          !aLength, "Range does not support nullptr with non-zero length.");
+      // ...because merely having a pointer to `nullptr + 1` is undefined
+      // behavior. UBSAN catches this as of clang-10.
+    }
+  }
+  Range(const RangedPtr<T>& aStart, const RangedPtr<T>& aEnd)
+      : mStart(aStart.get(), aStart.get(), aEnd.get()),
+        mEnd(aEnd.get(), aStart.get(), aEnd.get()) {
+    // Only accept two RangedPtrs within the same range.
+    aStart.checkIdenticalRange(aEnd);
+    MOZ_ASSERT_DEBUG_OR_FUZZING(aStart <= aEnd);
+  }
+
+  template <typename U, class = std::enable_if_t<
+                            std::is_convertible_v<U (*)[], T (*)[]>, int>>
+  MOZ_IMPLICIT Range(const Range<U>& aOther)
+      : mStart(aOther.mStart), mEnd(aOther.mEnd) {}
+
+  MOZ_IMPLICIT Range(Span<T> aSpan) : Range(aSpan.Elements(), aSpan.Length()) {}
+
+  template <typename U, class = std::enable_if_t<
+                            std::is_convertible_v<U (*)[], T (*)[]>, int>>
+  MOZ_IMPLICIT Range(const Span<U>& aSpan)
+      : Range(aSpan.Elements(), aSpan.Length()) {}
+
+  RangedPtr<T> begin() const { return mStart; }
+  RangedPtr<T> end() const { return mEnd; }
+  size_t length() const { return mEnd - mStart; }
+
+  T& operator[](size_t aOffset) const { return mStart[aOffset]; }
+
+  explicit operator bool() const { return mStart != nullptr; }
+
+  operator Span<T>() { return Span<T>(mStart.get(), length()); }
+
+  operator Span<const T>() const { return Span<T>(mStart.get(), length()); }
+};
+
+template <typename T>
+Span(Range<T>&) -> Span<T>;
+
+template <typename T>
+Span(const Range<T>&) -> Span<const T>;
+
+}  // namespace mozilla
+
+#endif /* mozilla_Range_h */