Have a faster way of iterating down the columns of a table. Bug 352461,

r=bernd, sr=roc

layout/tables/BasicTableLayoutStrategy.cpp

@@ -269,15 +269,10 @@ BasicTableLayoutStrategy::ComputeColumnIntrinsicWidths(nsIRenderingContext* aRen
 
         // Consider the contents of and the widths on the cells without
         // colspans.
-        for (PRInt32 row = 0, row_end = cellMap->GetRowCount();
-             row < row_end; ++row) {
-            PRBool originates;
-            PRInt32 colSpan;
-            nsTableCellFrame *cellFrame =
-                cellMap->GetCellInfoAt(row, col, &originates, &colSpan);
-            if (!cellFrame || !originates) {
-                continue;
-            }
+        nsCellMapColumnIterator columnIter(cellMap, col);
+        PRInt32 row, colSpan;
+        nsTableCellFrame* cellFrame;
+        while ((cellFrame = columnIter.GetNextFrame(&row, &colSpan))) {
             if (colSpan > 1) {
                 spanningCells.AddCell(colSpan, row, col);
                 continue;

layout/tables/nsCellMap.cpp

@@ -2679,3 +2679,90 @@ CellData* nsCellMap::AllocCellData(nsTableCellFrame* aOrigCell)
   }
   return data;
 }
+
+void
+nsCellMapColumnIterator::AdvanceRowGroup()
+{
+  mCurMap = mCurMap->GetNextSibling();
+
+  /* mCurMap could now be null, if we just handled the last originating cell.
+     Future calls will end up with mFoundCells == mOrigCells, but for this
+     one mFoundCells was definitely not big enough if we got here... */
+  mCurMapRowCount = mCurMap ? mCurMap->GetRowCount() : 0;
+
+  // Set mRow to 0, since cells can't span across table row groups.
+  mRow = 0;
+}
+
+void
+nsCellMapColumnIterator::IncrementRow(PRInt32 aIncrement)
+{
+  NS_PRECONDITION(aIncrement >= 0, "Bogus increment");
+  NS_PRECONDITION(mCurMap, "Bogus mOrigCells?");
+  if (aIncrement == 0) {
+    // This will span to the end of the row group
+    AdvanceRowGroup();
+  }
+  else {
+    mRow += aIncrement;
+    if (mRow >= mCurMapRowCount) {
+      AdvanceRowGroup();
+    }
+  }
+}
+
+nsTableCellFrame*
+nsCellMapColumnIterator::GetNextFrame(PRInt32* aRow, PRInt32* aColSpan)
+{
+  // Fast-path for the case when we don't have anything left in the column and
+  // we know it.
+  if (mFoundCells == mOrigCells) {
+    *aRow = 0;
+    *aColSpan = 1;
+    return nsnull;
+  }
+
+  while (1) {
+    NS_ASSERTION(mRow < mCurMapRowCount, "Bogus mOrigCells?");
+    // Safe to just get the row (which is faster than calling GetDataAt(), but
+    // there may not be that many cells in it, so have to use SafeElementAt for
+    // the mCol.
+    const nsCellMap::CellDataArray& row = mCurMap->mRows[mRow];
+    CellData* cellData = row.SafeElementAt(mCol);
+    if (!cellData || cellData->IsDead()) {
+      // Could hit this if there are fewer cells in this row than others, for
+      // example.
+      IncrementRow(1);
+      continue;
+    }
+
+    if (cellData->IsColSpan()) {
+      // Look up the originating data for this cell, advance by its rowspan.
+      CellData* origData = row[mCol - cellData->GetColSpanOffset()];
+      NS_ASSERTION(origData && origData->IsOrig() && origData->GetCellFrame(),
+                   "Must have usable originating data here");
+      IncrementRow(origData->GetCellFrame()->GetRowSpan());
+      continue;
+    }
+
+    NS_ASSERTION(cellData->IsOrig(),
+                 "Must have originating cellData by this point.  "
+                 "See comment on mRow in header.");
+
+    nsTableCellFrame* cellFrame = cellData->GetCellFrame();
+    NS_ASSERTION(cellFrame, "Orig data without cellframe?");
+    
+    *aRow = mRow;
+    PRBool ignoredZeroSpan;
+    *aColSpan = mCurMap->GetEffectiveColSpan(*mMap, mRow, mCol, ignoredZeroSpan);
+
+    IncrementRow(cellFrame->GetRowSpan());
+
+    ++mFoundCells;
+
+    return cellFrame;
+  }
+
+  NS_NOTREACHED("Can't get here");
+  return nsnull;
+}

layout/tables/nsCellMap.h

@@ -51,6 +51,7 @@ class nsTableRowGroupFrame;
 class nsTableFrame;
 class nsCellMap;
 class nsPresContext;
+class nsCellMapColumnIterator;
 
 struct nsColInfo
 {
@@ -233,6 +234,8 @@ protected:
   friend class nsCellMap;
   friend class BCMapCellIterator;
   friend class BCMapBorderIterator;
+  friend class nsCellMapColumnIterator;
+  
 /** Insert a row group cellmap after aPrevMap, if aPrefMap is null insert it
   * at the beginning, the ordering of the cellmap corresponds to the ordering of
   * rowgroups once OrderRowGroups has been called
@@ -403,6 +406,7 @@ protected:
   friend class BCMapCellIterator;
   friend class BCMapBorderIterator;
   friend class nsTableFrame;
+  friend class nsCellMapColumnIterator;
 
   /**
    * Increase the number of rows in this cellmap by aNumRows.  Put the
@@ -539,6 +543,47 @@ protected:
   nsCOMPtr<nsPresContext> mPresContext;
 };
 
+/**
+ * A class for iterating the cells in a given column.  Must be given a
+ * non-null nsTableCellMap and a column number valid for that cellmap.
+ */
+class nsCellMapColumnIterator
+{
+public:
+  nsCellMapColumnIterator(const nsTableCellMap* aMap, PRInt32 aCol) :
+    mMap(aMap), mCurMap(aMap->mFirstMap), mRow(0), mCol(aCol), mFoundCells(0)
+  {
+    NS_PRECONDITION(aMap, "Must have map");
+    NS_PRECONDITION(mCol < aMap->GetColCount(), "Invalid column");
+    mOrigCells = aMap->GetNumCellsOriginatingInCol(mCol);
+    if (mCurMap) {
+      mCurMapRowCount = mCurMap->GetRowCount();
+    }
+  }
+
+  nsTableCellFrame* GetNextFrame(PRInt32* aRow, PRInt32* aColSpan);
+  
+private:
+  void AdvanceRowGroup();
+
+  // Advance the row; aIncrement is considered to be a cell's rowspan,
+  // so if 0 is passed in we'll advance to the next rowgroup.
+  void IncrementRow(PRInt32 aIncrement);
+
+  const nsTableCellMap* mMap;
+  const nsCellMap* mCurMap;
+  // In steady-state mRow is the row in our current nsCellMap that we'll use
+  // the next time GetNextFrame() is called.  Due to the way we skip over
+  // rowspans, the entry in mRow and mCol is either null, dead, originating, or
+  // a colspan.  In particular, it cannot be a rowspan or overlap entry.
+  PRUint32 mRow;
+  const PRInt32 mCol;
+  PRUint32 mOrigCells;
+  PRUint32 mFoundCells;
+  PRUint32 mCurMapRowCount;
+};
+
+
 /* ----- inline methods ----- */
 inline PRInt32 nsTableCellMap::GetColCount() const
 {