Color dodge and burn with SkPMFloat.

src/opts/SkNx_sse.h

Index: src/opts/SkNx_sse.h
diff --git a/src/opts/SkNx_sse.h b/src/opts/SkNx_sse.h
index 9b4de700ee67aa4f81da20da09f7d42ed9af9c3a..2d3acbe45972e79400d56b5693b8cb356ad4e26e 100644
--- a/src/opts/SkNx_sse.h
+++ b/src/opts/SkNx_sse.h
@@ -193,6 +193,11 @@ public:
     bool allTrue() const { return 0xffff == _mm_movemask_epi8(_mm_castps_si128(fVec)); }
     bool anyTrue() const { return 0x0000 != _mm_movemask_epi8(_mm_castps_si128(fVec)); }
 
+    SkNf thenElse(const SkNf& t, const SkNf& e) const {
+        return _mm_or_ps(_mm_and_ps   (fVec, t.fVec),
+                         _mm_andnot_ps(fVec, e.fVec));
+    }
+
     __m128 fVec;
 };