layout/tables/SpanningCellSorter.h

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 // vim:cindent:ts=4:et:sw=4:
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef SpanningCellSorter_h
   8 #define SpanningCellSorter_h
   9
  10 /*
  11  * Code to sort cells by their colspan, used by BasicTableLayoutStrategy.
  12  */
  13
  14 #include "PLDHashTable.h"
  15 #include "nsDebug.h"
  16 #include "nsTArray.h"
  17 #include "StackArena.h"
  18
  19 /**
  20  * The SpanningCellSorter is responsible for accumulating lists of cells
  21  * with colspans so that those cells can later be enumerated, sorted
  22  * from lowest number of columns spanned to highest.  It does not use a
  23  * stable sort (in fact, it currently reverses).
  24  */
  25 class MOZ_STACK_CLASS SpanningCellSorter {
  26  public:
  27   SpanningCellSorter();
  28   ~SpanningCellSorter();
  29
  30   struct Item {
  31     int32_t row, col;
  32     Item* next;
  33   };
  34
  35   /**
  36    * Add a cell to the sorter.  Returns false on out of memory.
  37    * aColSpan is the number of columns spanned, and aRow/aCol are the
  38    * position of the cell in the table (for GetCellInfoAt).
  39    */
  40   bool AddCell(int32_t aColSpan, int32_t aRow, int32_t aCol);
  41
  42   /**
  43    * Get the next *list* of cells.  Each list contains all the cells
  44    * for a colspan value, and the lists are given in order from lowest
  45    * to highest colspan.  The colspan value is filled in to *aColSpan.
  46    */
  47   Item* GetNext(int32_t* aColSpan);
  48
  49  private:
  50   enum State { ADDING, ENUMERATING_ARRAY, ENUMERATING_HASH, DONE };
  51   State mState;
  52
  53   // store small colspans in an array for fast sorting and
  54   // enumeration, and large colspans in a hash table
  55
  56   enum { ARRAY_BASE = 2 };
  57   enum { ARRAY_SIZE = 8 };
  58   Item* mArray[ARRAY_SIZE];
  59   int32_t SpanToIndex(int32_t aSpan) { return aSpan - ARRAY_BASE; }
  60   int32_t IndexToSpan(int32_t aIndex) { return aIndex + ARRAY_BASE; }
  61   bool UseArrayForSpan(int32_t aSpan) {
  62     NS_ASSERTION(SpanToIndex(aSpan) >= 0, "cell without colspan");
  63     return SpanToIndex(aSpan) < ARRAY_SIZE;
  64   }
  65
  66   PLDHashTable mHashTable;
  67   struct HashTableEntry : public PLDHashEntryHdr {
  68     int32_t mColSpan;
  69     Item* mItems;
  70   };
  71
  72   static const PLDHashTableOps HashTableOps;
  73
  74   static PLDHashNumber HashTableHashKey(const void* key);
  75   static bool HashTableMatchEntry(const PLDHashEntryHdr* hdr, const void* key);
  76
  77   static int CompareHashTableEntry(HashTableEntry* a, HashTableEntry* b);
  78
  79   /* state used only during enumeration */
  80   uint32_t mEnumerationIndex;  // into mArray or mSortedHashTable
  81   nsTArray<HashTableEntry*> mSortedHashTable;
  82
  83   /*
  84    * operator new is forbidden since we use the pres shell's stack
  85    * memory, which much be pushed and popped at points matching a
  86    * push/pop on the C++ stack.
  87    */
  88   void* operator new(size_t sz) noexcept(true) { return nullptr; }
  89 };
  90
  91 #endif