SKPMFloat: we can beat the naive loops when clamping

src/core/SkPMFloat.h

 #ifndef SkPM_DEFINED
 #define SkPM_DEFINED
 
 #include "SkTypes.h"
 #include "SkColor.h"
 #include "Sk4x.h"
 
 // A pre-multiplied color storing each component in the same order as SkPMColor,
 // but as a float in the range [0, 255].
 class SK_STRUCT_ALIGN(16) SkPMFloat {
 public:
     static SkPMFloat FromPMColor(SkPMColor c) { return SkPMFloat(c); }
     static SkPMFloat FromARGB(float a, float r, float g, float b) { return SkPMFloat(a,r,g,b); }
 
     // May be more efficient than one at a time.  No special alignment assumed for SkPMColors.
-    static void From4PMColors(SkPMFloat floats[4], const SkPMColor colors[4]) {
-        // TODO: specialize
-        for (int i = 0; i < 4; i++) { floats[i] = FromPMColor(colors[i]); }
-    }
+    static void From4PMColors(SkPMFloat[4], const SkPMColor[4]);
 
     explicit SkPMFloat(SkPMColor);
     SkPMFloat(float a, float r, float g, float b) {
         // TODO: faster when specialized?
         fColor[SK_A32_SHIFT / 8] = a;
         fColor[SK_R32_SHIFT / 8] = r;
         fColor[SK_G32_SHIFT / 8] = g;
         fColor[SK_B32_SHIFT / 8] = b;
     }
 
@@ skipping 14 matching lines @@
     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]; }
 
     // get() and clamped() round component values to the nearest integer.
     SkPMColor     get() const;  // May SkASSERT(this->isValid()).  Some implementations may clamp.
     SkPMColor clamped() const;  // Will clamp all values to [0, 255].  Then may assert isValid().
 
     // 4-at-a-time versions of get() and clamped().  Like From4PMColors(), no alignment assumed.
-    static void To4PMColors(SkPMColor colors[4], const SkPMFloat floats[4]) {
-        // TODO: specialize
-        for (int i = 0; i < 4; i++) { colors[i] = floats[i].get(); }
-    }
-    static void ClampTo4PMColors(SkPMColor colors[4], const SkPMFloat floats[4]) {
-        // TODO: specialize
-        for (int i = 0; i < 4; i++) { colors[i] = floats[i].clamped(); }
-    }
+    static void To4PMColors(SkPMColor[4], const SkPMFloat[4]);
+    static void ClampTo4PMColors(SkPMColor[4], const SkPMFloat[4]);
 
     bool isValid() const {
         return this->a() >= 0 && this->a() <= 255
             && this->r() >= 0 && this->r() <= this->a()
             && this->g() >= 0 && this->g() <= this->a()
             && this->b() >= 0 && this->b() <= this->a();
     }
 
 private:
     float fColor[4];
 };
 
 #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSSE3
     #include "../opts/SkPMFloat_SSSE3.h"
 #elif 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