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diff --git a/include/ixion/dirty_cell_tracker.hpp b/include/ixion/dirty_cell_tracker.hpp
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * 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 INCLUDED_IXION_DIRTY_CELL_TRACKER_HPP
+#define INCLUDED_IXION_DIRTY_CELL_TRACKER_HPP
+
+#include "address.hpp"
+
+#include <memory>
+
+namespace ixion {
+
+/**
+ * This class is designed to track in-direct dependencies of dirty formula
+ * cells.  A "dirty" formula cell is a formula cell whose result needs to be
+ * re-calculated because at least one of its references have their values
+ * updated.
+ *
+ * This class also takes volatile functions into account when determining
+ * the status of the formula cel result.  A volatile function is a cell
+ * function whose value needs to get re-calculated unconditionally on every
+ * re-calculation.  One example of a volatile function is NOW(), which
+ * returns the current time at the time of calculation.
+ */
+class IXION_DLLPUBLIC dirty_cell_tracker
+{
+    struct impl;
+    std::unique_ptr<impl> mp_impl;
+
+public:
+    dirty_cell_tracker(const dirty_cell_tracker&) = delete;
+    dirty_cell_tracker& operator= (const dirty_cell_tracker&) = delete;
+
+    dirty_cell_tracker();
+    ~dirty_cell_tracker();
+
+    /**
+     * Add a tracking relationship from a source cell or cell range to a
+     * destination cell or cell range.
+     *
+     * @param src source cell or cell range that includes reference to
+     *             (therefore listens to) the range.
+     * @param dest destination cell or range referenced tracked by the source
+     *             cell.
+     */
+    void add(const abs_range_t& src, const abs_range_t& dest);
+
+    /**
+     * Remove an existing tracking relationship from a source cell or cell
+     * range to a destination cell or cell range. If no such relationship
+     * exists, it does nothing.
+     *
+     * @param src cell or cell range that includes reference to the range.
+     * @param dest cell or range referenced by the cell.
+     */
+    void remove(const abs_range_t& src, const abs_range_t& dest);
+
+    /**
+     * Register a formula cell located at the specified position as volatile.
+     * Note that the caller should ensure that the cell at the specified
+     * position is indeed a formula cell.
+     *
+     * @param pos position of the cell to register as a volatile cell.
+     */
+    void add_volatile(const abs_range_t& pos);
+
+    /**
+     * Remove the specified cell position from the internal set of registered
+     * volatile formula cells.
+     *
+     * @param pos position of the cell to unregister as a volatile cell.
+     */
+    void remove_volatile(const abs_range_t& pos);
+
+    abs_range_set_t query_dirty_cells(const abs_range_t& modified_cell) const;
+
+    abs_range_set_t query_dirty_cells(const abs_range_set_t& modified_cells) const;
+
+    std::vector<abs_range_t> query_and_sort_dirty_cells(const abs_range_t& modified_cell) const;
+
+    std::vector<abs_range_t> query_and_sort_dirty_cells(
+        const abs_range_set_t& modified_cells, const abs_range_set_t* dirty_formula_cells = nullptr) const;
+
+    std::string to_string() const;
+
+    bool empty() const;
+};
+
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */