ARM Skia NEON patches - 07 - Equation simplification

src/core/SkXfermode.cpp

Index: src/core/SkXfermode.cpp
diff --git a/src/core/SkXfermode.cpp b/src/core/SkXfermode.cpp
index 2cfdcfa4b30e4f15293068885b79e8dc3ae03e75..3107e1929475b659e63ca044b46bb5021f5db82a 100644
--- a/src/core/SkXfermode.cpp
+++ b/src/core/SkXfermode.cpp
@@ -402,7 +402,10 @@ static SkPMColor difference_modeproc(SkPMColor src, SkPMColor dst) {
 // kExclusion_Mode
 static inline int exclusion_byte(int sc, int dc, int sa, int da) {

[djsollen, 2013/07/10 15:36:47]

we should update the signature to remove 'sa' and 'da' now that they aren't
used.

     // this equations is wacky, wait for SVG to confirm it
-    int r = sc * da + dc * sa - 2 * sc * dc + sc * (255 - da) + dc * (255 - sa);
+    //int r = sc * da + dc * sa - 2 * sc * dc + sc * (255 - da) + dc * (255 - sa);
+
+    // The above equation can be simplified as follows
+    int r = 255*(sc + dc) - 2 * sc * dc;
     return clamp_div255round(r);
 }
 static SkPMColor exclusion_modeproc(SkPMColor src, SkPMColor dst) {