Improve QHeaderView::sectionsInserted performance

Old implementation had complexity O(oldSectionCount); replace it with
O(hiddenSectionCount) algorithm. This boosts performance in case of the
vertical headers for models with big row count.

Change-Id: I7bb02f5579ce83fbdecf5f8c3aa7dcc0ac60dd40
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index 66ff472724..bca315f80b 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -1879,13 +1879,13 @@ void QHeaderView::sectionsInserted(const QModelIndex &parent,
 
     // insert sections into hiddenSectionSize
     QHash<int, int> newHiddenSectionSize; // from logical index to section size
-    for (int i = 0; i < logicalFirst; ++i)
-        if (isSectionHidden(i))
-            newHiddenSectionSize[i] = d->hiddenSectionSize[i];
-    for (int j = logicalLast + 1; j < d->sectionCount(); ++j)
-        if (isSectionHidden(j))
-            newHiddenSectionSize[j] = d->hiddenSectionSize[j - insertCount];
-    d->hiddenSectionSize = newHiddenSectionSize;
+    for (QHash<int, int>::const_iterator it = d->hiddenSectionSize.cbegin(),
+         end = d->hiddenSectionSize.cend(); it != end; ++it) {
+        const int oldIndex = it.key();
+        const int newIndex = (oldIndex < logicalFirst) ? oldIndex : oldIndex + insertCount;
+        newHiddenSectionSize[newIndex] = it.value();
+    }
+    d->hiddenSectionSize.swap(newHiddenSectionSize);
 
     d->doDelayedResizeSections();
     emit sectionCountChanged(oldCount, count());