Bug 1701942 - Use bitwise equality for font variation value comparisons. r=jfkthame

Just like we do for font sizes / size-adjust in gfxFontStyle.

Differential Revision: https://phabricator.services.mozilla.com/D110519

Author: emilio

gfx/2d/FontVariation.h

@@ -8,21 +8,21 @@
 #define MOZILLA_GFX_FONTVARIATION_H_
 
 #include <stdint.h>
+#include "mozilla/FloatingPoint.h"
 
-namespace mozilla {
-namespace gfx {
+namespace mozilla::gfx {
 
 // An OpenType variation tag and value pair
 struct FontVariation {
   uint32_t mTag;
   float mValue;
 
   bool operator==(const FontVariation& aOther) const {
-    return mTag == aOther.mTag && mValue == aOther.mValue;
+    return mTag == aOther.mTag &&
+           NumbersAreBitwiseIdentical(mValue, aOther.mValue);
   }
 };
 
-}  // namespace gfx
-}  // namespace mozilla
+}  // namespace mozilla::gfx
 
 #endif /* MOZILLA_GFX_FONTVARIATION_H_ */

gfx/thebes/gfxFont.h

@@ -219,8 +219,7 @@ struct gfxFontStyle {
   }
 
   bool Equals(const gfxFontStyle& other) const {
-    return (*reinterpret_cast<const uint64_t*>(&size) ==
-            *reinterpret_cast<const uint64_t*>(&other.size)) &&
+    return mozilla::NumbersAreBitwiseIdentical(size, other.size) &&
            (style == other.style) && (weight == other.weight) &&
            (stretch == other.stretch) && (variantCaps == other.variantCaps) &&
            (variantSubSuper == other.variantSubSuper) &&
@@ -230,8 +229,7 @@ struct gfxFontStyle {
            (printerFont == other.printerFont) &&
            (useGrayscaleAntialiasing == other.useGrayscaleAntialiasing) &&
            (baselineOffset == other.baselineOffset) &&
-           (*reinterpret_cast<const uint32_t*>(&sizeAdjust) ==
-            *reinterpret_cast<const uint32_t*>(&other.sizeAdjust)) &&
+           mozilla::NumbersAreBitwiseIdentical(sizeAdjust, other.sizeAdjust) &&
            (featureSettings == other.featureSettings) &&
            (variantAlternates == other.variantAlternates) &&
            (featureValueLookup == other.featureValueLookup) &&

mfbt/FloatingPoint.h

@@ -524,14 +524,22 @@ static MOZ_ALWAYS_INLINE T UnspecifiedNaN() {
  */
 template <typename T>
 static inline bool NumbersAreIdentical(T aValue1, T aValue2) {
-  typedef FloatingPoint<T> Traits;
-  typedef typename Traits::Bits Bits;
+  using Bits = typename FloatingPoint<T>::Bits;
   if (IsNaN(aValue1)) {
     return IsNaN(aValue2);
   }
   return BitwiseCast<Bits>(aValue1) == BitwiseCast<Bits>(aValue2);
 }
 
+/**
+ * Compare two floating point values for bit-wise equality.
+ */
+template <typename T>
+static inline bool NumbersAreBitwiseIdentical(T aValue1, T aValue2) {
+  using Bits = typename FloatingPoint<T>::Bits;
+  return BitwiseCast<Bits>(aValue1) == BitwiseCast<Bits>(aValue2);
+}
+
 /**
  * Return true iff |aValue| and |aValue2| are equal (ignoring sign if both are
  * zero) or both NaN.