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diff --git a/layout/tables/SpanningCellSorter.h b/layout/tables/SpanningCellSorter.h
new file mode 100644
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+++ b/layout/tables/SpanningCellSorter.h
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+// vim:cindent:ts=4:et:sw=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 SpanningCellSorter_h
+#define SpanningCellSorter_h
+
+/*
+ * Code to sort cells by their colspan, used by BasicTableLayoutStrategy.
+ */
+
+#include "PLDHashTable.h"
+#include "nsDebug.h"
+#include "StackArena.h"
+
+/**
+ * The SpanningCellSorter is responsible for accumulating lists of cells
+ * with colspans so that those cells can later be enumerated, sorted
+ * from lowest number of columns spanned to highest.  It does not use a
+ * stable sort (in fact, it currently reverses).
+ */
+class MOZ_STACK_CLASS SpanningCellSorter {
+public:
+    SpanningCellSorter();
+    ~SpanningCellSorter();
+
+    struct Item {
+        int32_t row, col;
+        Item *next;
+    };
+
+    /**
+     * Add a cell to the sorter.  Returns false on out of memory.
+     * aColSpan is the number of columns spanned, and aRow/aCol are the
+     * position of the cell in the table (for GetCellInfoAt).
+     */
+    bool AddCell(int32_t aColSpan, int32_t aRow, int32_t aCol);
+
+    /**
+     * Get the next *list* of cells.  Each list contains all the cells
+     * for a colspan value, and the lists are given in order from lowest
+     * to highest colspan.  The colspan value is filled in to *aColSpan.
+     */
+    Item* GetNext(int32_t *aColSpan);
+private:
+
+    enum State { ADDING, ENUMERATING_ARRAY, ENUMERATING_HASH, DONE };
+    State mState;
+
+    // store small colspans in an array for fast sorting and
+    // enumeration, and large colspans in a hash table
+
+    enum { ARRAY_BASE = 2 };
+    enum { ARRAY_SIZE = 8 };
+    Item *mArray[ARRAY_SIZE];
+    int32_t SpanToIndex(int32_t aSpan) { return aSpan - ARRAY_BASE; }
+    int32_t IndexToSpan(int32_t aIndex) { return aIndex + ARRAY_BASE; }
+    bool UseArrayForSpan(int32_t aSpan) {
+        NS_ASSERTION(SpanToIndex(aSpan) >= 0, "cell without colspan");
+        return SpanToIndex(aSpan) < ARRAY_SIZE;
+    }
+
+    PLDHashTable mHashTable;
+    struct HashTableEntry : public PLDHashEntryHdr {
+        int32_t mColSpan;
+        Item *mItems;
+    };
+
+    static const PLDHashTableOps HashTableOps;
+
+    static PLDHashNumber HashTableHashKey(const void *key);
+    static bool
+        HashTableMatchEntry(const PLDHashEntryHdr *hdr, const void *key);
+
+    static int SortArray(const void *a, const void *b, void *closure);
+
+    /* state used only during enumeration */
+    uint32_t mEnumerationIndex; // into mArray or mSortedHashTable
+    HashTableEntry **mSortedHashTable;
+
+    /*
+     * operator new is forbidden since we use the pres shell's stack
+     * memory, which much be pushed and popped at points matching a
+     * push/pop on the C++ stack.
+     */
+    void* operator new(size_t sz) CPP_THROW_NEW { return nullptr; }
+};
+
+#endif