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diff --git a/include/svl/IndexedStyleSheets.hxx b/include/svl/IndexedStyleSheets.hxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * 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_SVL_INDEXEDSTYLESHEETS_HXX
+#define INCLUDED_SVL_INDEXEDSTYLESHEETS_HXX
+
+#include <svl/style.hxx>
+#include <rtl/ustring.hxx>
+#include <rtl/ref.hxx>
+
+#include <svl/svldllapi.h>
+
+#include <unordered_map>
+#include <vector>
+
+namespace svl
+{
+/** Function object to check whether a style sheet a fulfills specific criteria.
+ * Derive from this class and override the Check() method.
+ */
+struct StyleSheetPredicate
+{
+    virtual bool Check(const SfxStyleSheetBase& styleSheet) = 0;
+    virtual ~StyleSheetPredicate() {}
+};
+
+/** Function object for cleanup-Strategy for IndexedSfxStyleSheets::Clear().
+ * Derive from it and do what is necessary to dispose of a style sheet in Dispose().
+ */
+struct StyleSheetDisposer
+{
+    virtual void Dispose(rtl::Reference<SfxStyleSheetBase> styleSheet) = 0;
+    virtual ~StyleSheetDisposer() {}
+};
+
+/** Function object to apply a method on all style sheets.
+ * Derive from it and do whatever you want to with the style sheet in the DoIt() method.
+ */
+struct StyleSheetCallback
+{
+    virtual void DoIt(const SfxStyleSheetBase& styleSheet) = 0;
+    virtual ~StyleSheetCallback() {}
+};
+
+/** This class holds SfxStyleSheets and allows for access via an id and a name.
+ *
+ * @warning
+ * The identification of style sheets happens by their name. If the name of a sheet changes,
+ * it will not be found again! Please call Reindex() after changing a style sheet's name.
+ *
+ * @internal
+ * This class was implemented to mitigate solve #fdo 30770.
+ * The issue describes an Excel file which takes several hours to open.
+ * An analysis revealed that the time is spent searching for style sheets with linear scans in an array.
+ * This class implements access to the style sheets via their name in (usually) constant time.
+ *
+ * The return type for most methods is a vector of unsigned integers which denote the position
+ * of the style sheets in the vector, and not of pointers to style sheets.
+ * You will need a non-const StyleSheetPool to obtain the actual style sheets.
+ *
+ *
+ * Index-based access is required in several code portions. Hence we have to store the style sheets
+ * in a vector as well as in a map.
+ */
+class SVL_DLLPUBLIC IndexedStyleSheets final
+{
+public:
+    IndexedStyleSheets();
+
+    /** Destructor.
+     *
+     * @internal
+     * Is explicit because it has to know how to dispose of SfxStyleSheetBase objects.
+     */
+    ~IndexedStyleSheets();
+
+    /** Adds a style sheet.
+     *
+     * If the style sheet is already contained, this call has no effect.
+     */
+    void AddStyleSheet(const rtl::Reference<SfxStyleSheetBase>& style);
+
+    /** Removes a style sheet. */
+    bool RemoveStyleSheet(const rtl::Reference<SfxStyleSheetBase>& style);
+
+    /** Check whether a specified style sheet is stored. */
+    bool HasStyleSheet(const rtl::Reference<SfxStyleSheetBase>& style) const;
+
+    /** Obtain the number of style sheets which are held */
+    sal_Int32 GetNumberOfStyleSheets() const;
+
+    /** Obtain the number of style sheets for which a certain condition holds */
+    sal_Int32 GetNumberOfStyleSheetsWithPredicate(StyleSheetPredicate& predicate) const;
+
+    /** Return the stylesheet by its position.
+     * You can obtain the position by, e.g., FindStyleSheetPosition()
+     * @internal
+     * Method is not const because the returned style sheet is not const
+     */
+    SfxStyleSheetBase* GetStyleSheetByPosition(sal_Int32 pos);
+
+    /** Find the position of a provided style.
+     *
+     * @throws std::runtime_error if the style has not been found.
+     */
+    sal_Int32 FindStyleSheetPosition(const SfxStyleSheetBase& style) const;
+
+    /** Obtain the positions of all styles which have a given name
+     */
+    std::vector<sal_Int32> FindPositionsByName(const OUString& name) const;
+
+    enum class SearchBehavior
+    {
+        ReturnAll,
+        ReturnFirst
+    };
+    /** Obtain the positions of all styles which have a certain name and fulfill a certain condition.
+     *
+     * This method is fast because it can use the name-based index
+     */
+    std::vector<sal_Int32>
+    FindPositionsByNameAndPredicate(const OUString& name, StyleSheetPredicate& predicate,
+                                    SearchBehavior behavior = SearchBehavior::ReturnAll) const;
+
+    /** Obtain the positions of all styles which fulfill a certain condition.
+     *
+     * This method is slow because it cannot use the name-based index
+     */
+    std::vector<sal_Int32> FindPositionsByPredicate(StyleSheetPredicate& predicate) const;
+
+    /** Execute a callback on all style sheets */
+    void ApplyToAllStyleSheets(StyleSheetCallback& callback) const;
+
+    /** Clear the contents of the index.
+     * The StyleSheetDisposer::Dispose() method is called on each style sheet, e.g., if you want to broadcast
+     * changes.
+     */
+    void Clear(StyleSheetDisposer& cleanup);
+
+    void Reindex();
+
+    /** Warning: counting for n starts at 0, i.e., the 0th style sheet is the first that is found. */
+    SfxStyleSheetBase* GetNthStyleSheetThatMatchesPredicate(sal_Int32 n,
+                                                            StyleSheetPredicate& predicate,
+                                                            sal_Int32 startAt = 0);
+
+    /** Get the positions of the style sheets which belong to a certain family.
+     */
+    const std::vector<sal_Int32>& GetStyleSheetPositionsByFamily(SfxStyleFamily) const;
+
+private:
+    /** Register the position of a styleName in the index */
+    void Register(const SfxStyleSheetBase& style, sal_Int32 pos);
+
+    typedef std::vector<rtl::Reference<SfxStyleSheetBase>> VectorType;
+    /** Vector with the stylesheets to allow for index-based access.
+     */
+    VectorType mStyleSheets;
+
+    /** The map type that is used to store the mapping from strings to ids in mStyleSheets
+     *
+     * @internal
+     * Must be an unordered map. A regular map is too slow for some files. */
+    typedef std::unordered_multimap<OUString, unsigned> MapType;
+
+    /** A map which stores the positions of style sheets by their name */
+    MapType mPositionsByName;
+
+    std::vector<std::vector<sal_Int32>> mStyleSheetPositionsByFamily;
+};
+
+} /* namespace svl */
+
+#endif // INCLUDED_SVL_INDEXEDSTYLESHEETS_HXX
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */