Replace mvd>2 + mvd>32 by MIN((mvd+28)*17>>9, 2)

same speed as far as i can meassure but it might have fewer branches on some
archs.
Idea from x264 / jason

Originally committed as revision 22027 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264_cabac.c

@@ -915,7 +915,7 @@ static int decode_cabac_mb_mvd( H264Context *h, int list, int n, int l ) {
     int ctxbase = (l == 0) ? 40 : 47;
     int mvd;
 
-    if(!get_cabac(&h->cabac, &h->cabac_state[ctxbase+(amvd>2) + (amvd>32)]))
+    if(!get_cabac(&h->cabac, &h->cabac_state[ctxbase+FFMIN(((amvd+28)*17)>>9,2)]))
         return 0;
 
     mvd= 1;