--- a/gfx/2d/Types.h
+++ b/gfx/2d/Types.h
@@ -479,11 +479,16 @@ constexpr Corner HalfToFullCorner(HalfCo
   return Corner(aHalfCorner / 2);
 }
 
 constexpr HalfCorner FullToHalfCorner(Corner aCorner, bool aIsVertical)
 {
   return HalfCorner(aCorner * 2 + aIsVertical);
 }
 
+constexpr bool SideIsVertical(Side aSide)
+{
+  return aSide % 2;
+}
+
 } // namespace mozilla
 
 #endif /* MOZILLA_GFX_TYPES_H_ */

--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -1301,17 +1301,17 @@ nsIFrame::ComputeBorderRadii(const nsSty
   // css3-background specifies this algorithm for reducing
   // corner radii when they are too big.
   bool haveRadius = false;
   double ratio = 1.0f;
   NS_FOR_CSS_SIDES(side) {
     uint32_t hc1 = NS_SIDE_TO_HALF_CORNER(side, false, true);
     uint32_t hc2 = NS_SIDE_TO_HALF_CORNER(side, true, true);
     nscoord length =
-      NS_SIDE_IS_VERTICAL(side) ? aBorderArea.height : aBorderArea.width;
+      SideIsVertical(side) ? aBorderArea.height : aBorderArea.width;
     nscoord sum = aRadii[hc1] + aRadii[hc2];
     if (sum)
       haveRadius = true;
 
     // avoid floating point division in the normal case
     if (length < sum)
       ratio = std::min(ratio, double(length)/sum);
   }

--- a/layout/painting/nsCSSRendering.cpp
+++ b/layout/painting/nsCSSRendering.cpp
@@ -4059,19 +4059,19 @@ DrawBorderImage(nsPresContext*       aPr
   renderer.SetPreferredSize(intrinsicSize, imageSize);
 
   // Compute the used values of 'border-image-slice' and 'border-image-width';
   // we do them together because the latter can depend on the former.
   nsMargin slice;
   nsMargin border;
   NS_FOR_CSS_SIDES(s) {
     nsStyleCoord coord = aStyleBorder.mBorderImageSlice.Get(s);
-    int32_t imgDimension = NS_SIDE_IS_VERTICAL(s)
+    int32_t imgDimension = SideIsVertical(s)
                            ? imageSize.width : imageSize.height;
-    nscoord borderDimension = NS_SIDE_IS_VERTICAL(s)
+    nscoord borderDimension = SideIsVertical(s)
                            ? borderImgArea.width : borderImgArea.height;
     double value;
     switch (coord.GetUnit()) {
       case eStyleUnit_Percent:
         value = coord.GetPercentValue() * imgDimension;
         break;
       case eStyleUnit_Factor:
         value = nsPresContext::CSSPixelsToAppUnits(

--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -15,17 +15,16 @@
 // XXX fold this into nsStyleContext and group by nsStyleXXX struct
 
 namespace mozilla {
 
 // The results of these conversion macros are exhaustively checked in
 // nsStyleCoord.cpp.
 // Arguments must not have side effects.
 
-#define NS_SIDE_IS_VERTICAL(side_) ((side_) % 2)
 #define NS_SIDE_TO_FULL_CORNER(side_, second_) \
   (((side_) + !!(second_)) % 4)
 #define NS_SIDE_TO_HALF_CORNER(side_, second_, parallel_) \
   ((((side_) + !!(second_))*2 + ((side_) + !(parallel_))%2) % 8)
 
 // Basic shapes
 enum class StyleBasicShapeType : uint8_t {
   Polygon,

--- a/layout/style/nsStyleCoord.cpp
+++ b/layout/style/nsStyleCoord.cpp
@@ -325,20 +325,20 @@ nsStyleCorners::operator==(const nsStyle
 
 void nsStyleCorners::Reset()
 {
   NS_FOR_CSS_HALF_CORNERS(i) {
     nsStyleCoord::Reset(mUnits[i], mValues[i]);
   }
 }
 
-// Validation of NS_SIDE_IS_VERTICAL and NS_HALF_CORNER_IS_X.
+// Validation of SideIsVertical.
 #define CASE(side, result)                                                    \
-  static_assert(NS_SIDE_IS_VERTICAL(side) == result,                      \
-                "NS_SIDE_IS_VERTICAL is wrong")
+  static_assert(SideIsVertical(side) == result,                               \
+                "SideIsVertical is wrong")
 CASE(eSideTop,    false);
 CASE(eSideRight,  true);
 CASE(eSideBottom, false);
 CASE(eSideLeft,   true);
 #undef CASE
 
 // Validation of HalfCornerIsX.
 #define CASE(corner, result)                                                  \