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diff --git a/mozglue/baseprofiler/public/ProfileBufferIndex.h b/mozglue/baseprofiler/public/ProfileBufferIndex.h
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+/* -*- Mode: C++; tab-width: 2; 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 ProfileBufferIndex_h
+#define ProfileBufferIndex_h
+
+#include "mozilla/Attributes.h"
+
+#include <cstddef>
+#include <cstdint>
+
+namespace mozilla {
+
+// Generic index into a Profiler buffer, mostly for internal usage.
+// Intended to appear infinite (it should effectively never wrap).
+// 0 (zero) is reserved as nullptr-like value; it may indicate failure result,
+// or it may point at the earliest available block.
+using ProfileBufferIndex = uint64_t;
+
+// Externally-opaque class encapsulating a block index, i.e. a
+// ProfileBufferIndex that is guaranteed to point at the start of a Profile
+// buffer block (until it is destroyed, but then that index cannot be reused and
+// functions should gracefully handle expired blocks).
+// Users may get these from Profile buffer functions, to later access previous
+// blocks; they should avoid converting and operating on their value.
+class ProfileBufferBlockIndex {
+ public:
+  // Default constructor with internal 0 value, for which Profile buffers must
+  // guarantee that it is before any valid entries; All public APIs should
+  // fail gracefully, doing and/or returning Nothing.
+  ProfileBufferBlockIndex() : mBlockIndex(0) {}
+
+  // Implicit conversion from literal `nullptr` to internal 0 value, to allow
+  // convenient init/reset/comparison with 0 index.
+  MOZ_IMPLICIT ProfileBufferBlockIndex(std::nullptr_t) : mBlockIndex(0) {}
+
+  // Explicit conversion to bool, works in `if` and other tests.
+  // Only returns false for default `ProfileBufferBlockIndex{}` value.
+  explicit operator bool() const { return mBlockIndex != 0; }
+
+  // Comparison operators. Default `ProfileBufferBlockIndex{}` value is always
+  // the lowest.
+  [[nodiscard]] bool operator==(const ProfileBufferBlockIndex& aRhs) const {
+    return mBlockIndex == aRhs.mBlockIndex;
+  }
+  [[nodiscard]] bool operator!=(const ProfileBufferBlockIndex& aRhs) const {
+    return mBlockIndex != aRhs.mBlockIndex;
+  }
+  [[nodiscard]] bool operator<(const ProfileBufferBlockIndex& aRhs) const {
+    return mBlockIndex < aRhs.mBlockIndex;
+  }
+  [[nodiscard]] bool operator<=(const ProfileBufferBlockIndex& aRhs) const {
+    return mBlockIndex <= aRhs.mBlockIndex;
+  }
+  [[nodiscard]] bool operator>(const ProfileBufferBlockIndex& aRhs) const {
+    return mBlockIndex > aRhs.mBlockIndex;
+  }
+  [[nodiscard]] bool operator>=(const ProfileBufferBlockIndex& aRhs) const {
+    return mBlockIndex >= aRhs.mBlockIndex;
+  }
+
+  // Explicit conversion to ProfileBufferIndex, mostly used by internal Profile
+  // buffer code.
+  [[nodiscard]] ProfileBufferIndex ConvertToProfileBufferIndex() const {
+    return mBlockIndex;
+  }
+
+  // Explicit creation from ProfileBufferIndex, mostly used by internal
+  // Profile buffer code.
+  [[nodiscard]] static ProfileBufferBlockIndex CreateFromProfileBufferIndex(
+      ProfileBufferIndex aIndex) {
+    return ProfileBufferBlockIndex(aIndex);
+  }
+
+ private:
+  // Private to prevent easy construction from any value. Use
+  // `CreateFromProfileBufferIndex()` instead.
+  // The main reason for this indirection is to make it harder to create these
+  // objects, because only the profiler code should need to do it. Ideally, this
+  // class should be used wherever a block index should be stored, but there is
+  // so much code that uses `uint64_t` that it would be a big task to change
+  // them all. So for now we allow conversions to/from numbers, but it's as ugly
+  // as possible to make sure it doesn't get too common; and if one day we want
+  // to tackle a global change, it should be easy to find all these locations
+  // thanks to the explicit conversion functions.
+  explicit ProfileBufferBlockIndex(ProfileBufferIndex aBlockIndex)
+      : mBlockIndex(aBlockIndex) {}
+
+  ProfileBufferIndex mBlockIndex;
+};
+
+}  // namespace mozilla
+
+#endif  // ProfileBufferIndex_h