--- a/gfx/2d/Types.h
+++ b/gfx/2d/Types.h
@@ -474,11 +474,16 @@ constexpr bool HalfCornerIsX(HalfCorner 
   return !(aHalfCorner % 2);
 }
 
 constexpr Corner HalfToFullCorner(HalfCorner aHalfCorner)
 {
   return Corner(aHalfCorner / 2);
 }
 
+constexpr HalfCorner FullToHalfCorner(Corner aCorner, bool aIsVertical)
+{
+  return HalfCorner(aCorner * 2 + aIsVertical);
+}
+
 } // namespace mozilla
 
 #endif /* MOZILLA_GFX_TYPES_H_ */

--- a/layout/style/StyleAnimationValue.cpp
+++ b/layout/style/StyleAnimationValue.cpp
@@ -4205,19 +4205,19 @@ StyleClipBasicShapeToCSSArray(const Styl
         if (!StyleCoordToCSSValue(coords[i], functionArray->Item(i + 1))) {
           return false;
         }
       }
       RefPtr<nsCSSValue::Array> radiusArray = nsCSSValue::Array::Create(4);
       const nsStyleCorners& radii = shape->GetRadius();
       NS_FOR_CSS_FULL_CORNERS(corner) {
         auto pair = MakeUnique<nsCSSValuePair>();
-        if (!StyleCoordToCSSValue(radii.Get(NS_FULL_TO_HALF_CORNER(corner, false)),
+        if (!StyleCoordToCSSValue(radii.Get(FullToHalfCorner(corner, false)),
                                   pair->mXValue) ||
-            !StyleCoordToCSSValue(radii.Get(NS_FULL_TO_HALF_CORNER(corner, true)),
+            !StyleCoordToCSSValue(radii.Get(FullToHalfCorner(corner, true)),
                                   pair->mYValue)) {
           return false;
         }
         radiusArray->Item(corner).SetPairValue(pair.get());
       }
       // Set the last item in functionArray to the radius array:
       functionArray->Item(functionArray->Count() - 1).
                        SetArrayValue(radiusArray, eCSSUnit_Array);
@@ -4687,21 +4687,21 @@ StyleAnimationValue::ExtractComputedValu
        eCornerBottomRight == eStyleAnimType_Corner_BottomRight -
                              eStyleAnimType_Corner_TopLeft        &&
        eCornerBottomLeft  == eStyleAnimType_Corner_BottomLeft -
                              eStyleAnimType_Corner_TopLeft,
        "box corner constants out of sync with animation corner constants");
 
       const nsStyleCorners& corners =
         StyleDataAtOffset<nsStyleCorners>(styleStruct, ssOffset);
-      uint8_t fullCorner = animType - eStyleAnimType_Corner_TopLeft;
+      Corner fullCorner = Corner(animType - eStyleAnimType_Corner_TopLeft);
       const nsStyleCoord &horiz =
-        corners.Get(NS_FULL_TO_HALF_CORNER(fullCorner, false));
+        corners.Get(FullToHalfCorner(fullCorner, false));
       const nsStyleCoord &vert =
-        corners.Get(NS_FULL_TO_HALF_CORNER(fullCorner, true));
+        corners.Get(FullToHalfCorner(fullCorner, true));
       nsAutoPtr<nsCSSValuePair> pair(new nsCSSValuePair);
       if (!StyleCoordToCSSValue(horiz, pair->mXValue) ||
           !StyleCoordToCSSValue(vert, pair->mYValue)) {
         return false;
       }
       aComputedValue.SetAndAdoptCSSValuePairValue(pair.forget(),
                                                   eUnit_CSSValuePair);
       return true;

--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -3408,20 +3408,20 @@ nsComputedDOMStyle::DoGetOutlineColor()
 {
   RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
   SetValueFromComplexColor(val, StyleOutline()->mOutlineColor);
   return val.forget();
 }
 
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::GetEllipseRadii(const nsStyleCorners& aRadius,
-                                    uint8_t aFullCorner)
-{
-  nsStyleCoord radiusX = aRadius.Get(NS_FULL_TO_HALF_CORNER(aFullCorner, false));
-  nsStyleCoord radiusY = aRadius.Get(NS_FULL_TO_HALF_CORNER(aFullCorner, true));
+                                    Corner aFullCorner)
+{
+  nsStyleCoord radiusX = aRadius.Get(FullToHalfCorner(aFullCorner, false));
+  nsStyleCoord radiusY = aRadius.Get(FullToHalfCorner(aFullCorner, true));
 
   // for compatibility, return a single value if X and Y are equal
   if (radiusX == radiusY) {
     RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
     SetValueToCoord(val, radiusX, true);
     return val.forget();
   }
 
@@ -5955,19 +5955,19 @@ nsComputedDOMStyle::BoxValuesToString(ns
 void
 nsComputedDOMStyle::BasicShapeRadiiToString(nsAString& aCssText,
                                             const nsStyleCorners& aCorners)
 {
   nsTArray<nsStyleCoord> horizontal, vertical;
   nsAutoString horizontalString, verticalString;
   NS_FOR_CSS_FULL_CORNERS(corner) {
     horizontal.AppendElement(
-      aCorners.Get(NS_FULL_TO_HALF_CORNER(corner, false)));
+      aCorners.Get(FullToHalfCorner(corner, false)));
     vertical.AppendElement(
-      aCorners.Get(NS_FULL_TO_HALF_CORNER(corner, true)));
+      aCorners.Get(FullToHalfCorner(corner, true)));
   }
   BoxValuesToString(horizontalString, horizontal);
   BoxValuesToString(verticalString, vertical);
   aCssText.Append(horizontalString);
   if (horizontalString == verticalString) {
     return;
   }
   aCssText.AppendLiteral(" / ");

--- a/layout/style/nsComputedDOMStyle.h
+++ b/layout/style/nsComputedDOMStyle.h
@@ -147,17 +147,17 @@ private:
 #define STYLE_STRUCT(name_, checkdata_cb_)                              \
   const nsStyle##name_ * Style##name_() {                               \
     return mStyleContext->Style##name_();                               \
   }
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
 
   already_AddRefed<CSSValue> GetEllipseRadii(const nsStyleCorners& aRadius,
-                                             uint8_t aFullCorner);
+                                             mozilla::Corner aFullCorner);
 
   already_AddRefed<CSSValue> GetOffsetWidthFor(mozilla::Side aSide);
 
   already_AddRefed<CSSValue> GetAbsoluteOffset(mozilla::Side aSide);
 
   already_AddRefed<CSSValue> GetRelativeOffset(mozilla::Side aSide);
 
   already_AddRefed<CSSValue> GetStickyOffset(mozilla::Side aSide);

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -7774,18 +7774,18 @@ nsRuleNode::ComputeBorderData(void* aSta
     }
   }
 
   // border-radius: length, percent, inherit
   {
     const nsCSSPropertyID* subprops =
       nsCSSProps::SubpropertyEntryFor(eCSSProperty_border_radius);
     NS_FOR_CSS_FULL_CORNERS(corner) {
-      int cx = NS_FULL_TO_HALF_CORNER(corner, false);
-      int cy = NS_FULL_TO_HALF_CORNER(corner, true);
+      int cx = FullToHalfCorner(corner, false);
+      int cy = FullToHalfCorner(corner, true);
       const nsCSSValue& radius = *aRuleData->ValueFor(subprops[corner]);
       nsStyleCoord parentX = parentBorder->mBorderRadius.Get(cx);
       nsStyleCoord parentY = parentBorder->mBorderRadius.Get(cy);
       nsStyleCoord coordX, coordY;
 
       if (SetPairCoords(radius, coordX, coordY, parentX, parentY,
                         SETCOORD_LPH | SETCOORD_INITIAL_ZERO |
                           SETCOORD_STORE_CALC | SETCOORD_UNSET_INITIAL,
@@ -7963,18 +7963,18 @@ nsRuleNode::ComputeOutlineData(void* aSt
                                  mPresContext,
                                  outline->mOutlineColor, conditions);
 
   // -moz-outline-radius: length, percent, inherit
   {
     const nsCSSPropertyID* subprops =
       nsCSSProps::SubpropertyEntryFor(eCSSProperty__moz_outline_radius);
     NS_FOR_CSS_FULL_CORNERS(corner) {
-      int cx = NS_FULL_TO_HALF_CORNER(corner, false);
-      int cy = NS_FULL_TO_HALF_CORNER(corner, true);
+      int cx = FullToHalfCorner(corner, false);
+      int cy = FullToHalfCorner(corner, true);
       const nsCSSValue& radius = *aRuleData->ValueFor(subprops[corner]);
       nsStyleCoord parentX = parentOutline->mOutlineRadius.Get(cx);
       nsStyleCoord parentY = parentOutline->mOutlineRadius.Get(cy);
       nsStyleCoord coordX, coordY;
 
       if (SetPairCoords(radius, coordX, coordY, parentX, parentY,
                         SETCOORD_LPH | SETCOORD_INITIAL_ZERO |
                           SETCOORD_STORE_CALC | SETCOORD_UNSET_INITIAL,
@@ -9825,18 +9825,18 @@ GetStyleBasicShapeFromCSSValue(const nsC
       }
       coords.AppendElement(inset);
     }
 
     nsStyleCorners& insetRadius = basicShape->GetRadius();
     if (shapeFunction->Item(5).GetUnit() == eCSSUnit_Array) {
       nsCSSValue::Array* radiiArray = shapeFunction->Item(5).GetArrayValue();
       NS_FOR_CSS_FULL_CORNERS(corner) {
-        int cx = NS_FULL_TO_HALF_CORNER(corner, false);
-        int cy = NS_FULL_TO_HALF_CORNER(corner, true);
+        int cx = FullToHalfCorner(corner, false);
+        int cy = FullToHalfCorner(corner, true);
         const nsCSSValue& radius = radiiArray->Item(corner);
         nsStyleCoord coordX, coordY;
         DebugOnly<bool> didSetRadii = SetPairCoords(radius, coordX, coordY,
                                                     nsStyleCoord(),
                                                     nsStyleCoord(), mask,
                                                     aStyleContext,
                                                     aPresContext,
                                                     aConditions);

--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -15,18 +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_FULL_TO_HALF_CORNER(var_, vert_) ((var_)*2 + !!(vert_))
-
 #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 {

--- a/layout/style/nsStyleCoord.cpp
+++ b/layout/style/nsStyleCoord.cpp
@@ -363,20 +363,20 @@ CASE(eCornerTopLeftY,     eCornerTopLeft
 CASE(eCornerTopRightX,    eCornerTopRight);
 CASE(eCornerTopRightY,    eCornerTopRight);
 CASE(eCornerBottomRightX, eCornerBottomRight);
 CASE(eCornerBottomRightY, eCornerBottomRight);
 CASE(eCornerBottomLeftX,  eCornerBottomLeft);
 CASE(eCornerBottomLeftY,  eCornerBottomLeft);
 #undef CASE
 
-// Validation of NS_FULL_TO_HALF_CORNER.
+// Validation of FullToHalfCorner.
 #define CASE(corner, vert, result)                                            \
-  static_assert(NS_FULL_TO_HALF_CORNER(corner, vert) == result,           \
-                "NS_FULL_TO_HALF_CORNER is wrong")
+  static_assert(FullToHalfCorner(corner, vert) == result,                     \
+                "FullToHalfCorner is wrong")
 CASE(eCornerTopLeft,     false, eCornerTopLeftX);
 CASE(eCornerTopLeft,     true,  eCornerTopLeftY);
 CASE(eCornerTopRight,    false, eCornerTopRightX);
 CASE(eCornerTopRight,    true,  eCornerTopRightY);
 CASE(eCornerBottomRight, false, eCornerBottomRightX);
 CASE(eCornerBottomRight, true,  eCornerBottomRightY);
 CASE(eCornerBottomLeft,  false, eCornerBottomLeftX);
 CASE(eCornerBottomLeft,  true,  eCornerBottomLeftY);