Use right-shift instead of division by two.

Patch by Dark Shikari

Originally committed as revision 23723 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo_common.h

@@ -580,11 +580,11 @@ static inline void chroma_4mv_motion(MpegEncContext *s,
 
     src_x = s->mb_x * 8 + mx;
     src_y = s->mb_y * 8 + my;
-    src_x = av_clip(src_x, -8, s->width/2);
-    if (src_x == s->width/2)
+    src_x = av_clip(src_x, -8, (s->width >> 1));
+    if (src_x == (s->width >> 1))
         dxy &= ~1;
-    src_y = av_clip(src_y, -8, s->height/2);
-    if (src_y == s->height/2)
+    src_y = av_clip(src_y, -8, (s->height >> 1));
+    if (src_y == (s->height >> 1))
         dxy &= ~2;
 
     offset = (src_y * (s->uvlinesize)) + src_x;