Don't guarantee any particular color order for SkPMFloat. Hide fColor.

src/core/SkPMFloat.h

 #ifndef SkPM_DEFINED
 #define SkPM_DEFINED
 
 #include "SkTypes.h"
 #include "SkColor.h"
 #include "Sk4x.h"
 
-// A pre-multiplied color in the same order as SkPMColor storing each component as a float.
-struct SK_STRUCT_ALIGN(16) SkPMFloat {
-    float fColor[4];
-
+// A pre-multiplied color storing each component as a float.
+class SK_STRUCT_ALIGN(16) SkPMFloat {
+public:
     // Normal POD copies and do-nothing initialization.
     SkPMFloat()                            = default;
     SkPMFloat(const SkPMFloat&)            = default;
     SkPMFloat& operator=(const SkPMFloat&) = default;
 
     // Freely autoconvert between SkPMFloat and Sk4f.
     /*implicit*/ SkPMFloat(const Sk4f& fs) { fs.storeAligned(fColor); }
     /*implicit*/ operator Sk4f() const { return Sk4f::LoadAligned(fColor); }
 
     float a() const { return fColor[SK_A32_SHIFT / 8]; }
     float r() const { return fColor[SK_R32_SHIFT / 8]; }
     float g() const { return fColor[SK_G32_SHIFT / 8]; }
     float b() const { return fColor[SK_B32_SHIFT / 8]; }
 
     void setA(float val) { fColor[SK_A32_SHIFT / 8] = val; }
     void setR(float val) { fColor[SK_R32_SHIFT / 8] = val; }
     void setG(float val) { fColor[SK_G32_SHIFT / 8] = val; }
     void setB(float val) { fColor[SK_B32_SHIFT / 8] = val; }
 
     void set(SkPMColor);
 
-    SkPMColor     get() const;  // May SkASSERT(this->isValid()).
+    SkPMColor     get() const;  // May SkASSERT(this->isValid()).  Some implementations may clamp.
     SkPMColor clamped() const;  // Will clamp all values to [0,1], then SkASSERT(this->isValid()).
 
     bool isValid() const {
         return this->a() >= 0 && this->a() <= 1
             && this->r() >= 0 && this->r() <= this->a()
             && this->g() >= 0 && this->g() <= this->a()
             && this->b() >= 0 && this->b() <= this->a();
     }
+
+private:
+    // We mirror SkPMColor order only to make set()/get()/clamped() as fast as possible.
+    float fColor[4];
 };
 
 #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
     #include "../opts/SkPMFloat_SSE2.h"
 #elif defined(__ARM_NEON__)
     #include "../opts/SkPMFloat_neon.h"
 #else
     #include "../opts/SkPMFloat_none.h"
 #endif
 
 #endif//SkPM_DEFINED