YUV scale filter columns improved filtering accuracy

source/scale_neon.cc

Index: source/scale_neon.cc
diff --git a/source/scale_neon.cc b/source/scale_neon.cc
index 95f3362a48477c9203a43ba399d93af39967a66e..26bb70592e7dfd8f546a6cc24a8270ec5d9a9bb0 100644
--- a/source/scale_neon.cc
+++ b/source/scale_neon.cc
@@ -572,6 +572,10 @@ void ScaleAddRows_NEON(const uint8* src_ptr, ptrdiff_t src_stride,
     MEMACCESS(6)                                               \
     "vld2.8     {d6["#n"], d7["#n"]}, [%6]     \n"
 
+// The NEON version mimics this formula:
+// #define BLENDER(a, b, f) (uint8)((int)(a) +
+//    ((int)(f) * ((int)(b) - (int)(a)) >> 16))
+
 void ScaleFilterCols_NEON(uint8* dst_ptr, const uint8* src_ptr,
                           int dst_width, int x, int dx) {
   int dx_offset[4] = {0, 1, 2, 3};