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diff --git a/layout/tables/SpanningCellSorter.h b/layout/tables/SpanningCellSorter.h
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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: 2 -*- */
+// 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) noexcept(true) { return nullptr; }
+};
+
+#endif