swscale: factor shift out of DITHER_COPY().

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/swscale.c

@@ -1859,19 +1859,20 @@ static int packedCopyWrapper(SwsContext *c, const uint8_t* src[], int srcStride[
 
 #define DITHER_COPY(dst, dstStride, src, srcStride)\
     for (i = 0; i < height; i++) {\
+        int shift= src_depth-dst_depth;\
         uint8_t *dither= dithers[src_depth-9][i&7];\
         for (j = 0; j < length-7; j+=8){\
-            dst[j+0] = (src[j+0] + dither[0])>>(src_depth-dst_depth);\
-            dst[j+1] = (src[j+1] + dither[1])>>(src_depth-dst_depth);\
-            dst[j+2] = (src[j+2] + dither[2])>>(src_depth-dst_depth);\
-            dst[j+3] = (src[j+3] + dither[3])>>(src_depth-dst_depth);\
-            dst[j+4] = (src[j+4] + dither[4])>>(src_depth-dst_depth);\
-            dst[j+5] = (src[j+5] + dither[5])>>(src_depth-dst_depth);\
-            dst[j+6] = (src[j+6] + dither[6])>>(src_depth-dst_depth);\
-            dst[j+7] = (src[j+7] + dither[7])>>(src_depth-dst_depth);\
+            dst[j+0] = (src[j+0] + dither[0])>>shift;\
+            dst[j+1] = (src[j+1] + dither[1])>>shift;\
+            dst[j+2] = (src[j+2] + dither[2])>>shift;\
+            dst[j+3] = (src[j+3] + dither[3])>>shift;\
+            dst[j+4] = (src[j+4] + dither[4])>>shift;\
+            dst[j+5] = (src[j+5] + dither[5])>>shift;\
+            dst[j+6] = (src[j+6] + dither[6])>>shift;\
+            dst[j+7] = (src[j+7] + dither[7])>>shift;\
         }\
         for (; j < length; j++)\
-            dst[j] = (src[j] + dither[j&7])>>(src_depth-dst_depth);\
+            dst[j] = (src[j] + dither[j&7])>>shift;\
         dst += dstStride;\
         src += srcStride;\
     }