Mask/background-repeat: round should round the number of tiles of an image to the nearest natural n…

Source/core/rendering/RenderBoxModelObject.cpp

Index: Source/core/rendering/RenderBoxModelObject.cpp
diff --git a/Source/core/rendering/RenderBoxModelObject.cpp b/Source/core/rendering/RenderBoxModelObject.cpp
index aada21668d2aeabe3d149fa3e8ad5fe5988748ad..b616443dd61f30c380829ede4d5dc2fff0fff31e 100644
--- a/Source/core/rendering/RenderBoxModelObject.cpp
+++ b/Source/core/rendering/RenderBoxModelObject.cpp
@@ -1062,8 +1062,7 @@ void RenderBoxModelObject::calculateBackgroundImageGeometry(const FillLayer* fil
 
     LayoutUnit computedXPosition = minimumValueForLength(fillLayer->xPosition(), availableWidth, renderView, true);
     if (backgroundRepeatX == RoundFill && positioningAreaSize.width() > 0 && fillTileSize.width() > 0) {
-        int nrTiles = ceil((double)positioningAreaSize.width() /
-            fillTileSize.width());
+        int nrTiles = static_cast<int>(round((float)positioningAreaSize.width() / fillTileSize.width()));

[eseidel, 2013/09/17 15:48:44]

We don't have a helper function do to this for us?  roundl?

[Julien - ping for review, 2013/09/17 16:26:27]

lround would do the trick (or lroundf if we want to keep single precision
arithmetic). There is one issue with this code though: it can overflow the int.
Reading roundl (and ceil(3) manual page), you can't just cast to int without a
check.

Is there a good reason the logic doesn't use long?

Also if you use single precision, let's use the function that take a single
precision to avoid implicit conversions (I don't have mind use single vs double
precision but let's be consistent).

 
         if (fillLayer->size().size.height().isAuto() && backgroundRepeatY != RoundFill) {
             fillTileSize.setHeight(fillTileSize.height() * positioningAreaSize.width() / (nrTiles * fillTileSize.width()));
@@ -1076,8 +1075,7 @@ void RenderBoxModelObject::calculateBackgroundImageGeometry(const FillLayer* fil
 
     LayoutUnit computedYPosition = minimumValueForLength(fillLayer->yPosition(), availableHeight, renderView, true);
     if (backgroundRepeatY == RoundFill && positioningAreaSize.height() > 0 && fillTileSize.height() > 0) {
-        int nrTiles = ceil((double)positioningAreaSize.height() /
-            fillTileSize.height());
+        int nrTiles = static_cast<int>(round((float)positioningAreaSize.height() / fillTileSize.height()));
 
         if (fillLayer->size().size.width().isAuto() && backgroundRepeatX != RoundFill) {
             fillTileSize.setWidth(fillTileSize.width() * positioningAreaSize.height() / (nrTiles * fillTileSize.height()));