Support lowres 3 when decoding MPEG video.

Patch by Anatoliy Nenashev, nenashev_as mail ru

Originally committed as revision 21239 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.c

@@ -1416,6 +1416,7 @@ static inline int hpel_motion_lowres(MpegEncContext *s,
                                   int motion_x, int motion_y)
 {
     const int lowres= s->avctx->lowres;
+    const int op_index= FFMIN(lowres, 2);
     const int s_mask= (2<<lowres)-1;
     int emu=0;
     int sx, sy;
@@ -1440,11 +1441,11 @@ static inline int hpel_motion_lowres(MpegEncContext *s,
         emu=1;
     }
 
-    sx <<= 2 - lowres;
-    sy <<= 2 - lowres;
+    sx= (sx << 2) >> lowres;
+    sy= (sy << 2) >> lowres;
     if(field_select)
         src += s->linesize;
-    pix_op[lowres](dest, src, stride, h, sx, sy);
+    pix_op[op_index](dest, src, stride, h, sx, sy);
     return emu;
 }
 
@@ -1458,6 +1459,7 @@ static av_always_inline void mpeg_motion_lowres(MpegEncContext *s,
     uint8_t *ptr_y, *ptr_cb, *ptr_cr;
     int mx, my, src_x, src_y, uvsrc_x, uvsrc_y, uvlinesize, linesize, sx, sy, uvsx, uvsy;
     const int lowres= s->avctx->lowres;
+    const int op_index= FFMIN(lowres, 2);
     const int block_s= 8>>lowres;
     const int s_mask= (2<<lowres)-1;
     const int h_edge_pos = s->h_edge_pos >> lowres;
@@ -1532,15 +1534,15 @@ static av_always_inline void mpeg_motion_lowres(MpegEncContext *s,
         ptr_cr+= s->uvlinesize;
     }
 
-    sx <<= 2 - lowres;
-    sy <<= 2 - lowres;
+    sx= (sx << 2) >> lowres;
+    sy= (sy << 2) >> lowres;
     pix_op[lowres-1](dest_y, ptr_y, linesize, h, sx, sy);
 
     if(!CONFIG_GRAY || !(s->flags&CODEC_FLAG_GRAY)){
-        uvsx <<= 2 - lowres;
-        uvsy <<= 2 - lowres;
-        pix_op[lowres](dest_cb, ptr_cb, uvlinesize, h >> s->chroma_y_shift, uvsx, uvsy);
-        pix_op[lowres](dest_cr, ptr_cr, uvlinesize, h >> s->chroma_y_shift, uvsx, uvsy);
+        uvsx= (uvsx << 2) >> lowres;
+        uvsy= (uvsy << 2) >> lowres;
+        pix_op[op_index](dest_cb, ptr_cb, uvlinesize, h >> s->chroma_y_shift, uvsx, uvsy);
+        pix_op[op_index](dest_cr, ptr_cr, uvlinesize, h >> s->chroma_y_shift, uvsx, uvsy);
     }
     //FIXME h261 lowres loop filter
 }
@@ -1551,6 +1553,7 @@ static inline void chroma_4mv_motion_lowres(MpegEncContext *s,
                                      h264_chroma_mc_func *pix_op,
                                      int mx, int my){
     const int lowres= s->avctx->lowres;
+    const int op_index= FFMIN(lowres, 2);
     const int block_s= 8>>lowres;
     const int s_mask= (2<<lowres)-1;
     const int h_edge_pos = s->h_edge_pos >> (lowres+1);
@@ -1583,16 +1586,16 @@ static inline void chroma_4mv_motion_lowres(MpegEncContext *s,
             emu=1;
         }
     }
-    sx <<= 2 - lowres;
-    sy <<= 2 - lowres;
-    pix_op[lowres](dest_cb, ptr, s->uvlinesize, block_s, sx, sy);
+    sx= (sx << 2) >> lowres;
+    sy= (sy << 2) >> lowres;
+    pix_op[op_index](dest_cb, ptr, s->uvlinesize, block_s, sx, sy);
 
     ptr = ref_picture[2] + offset;
     if(emu){
         ff_emulated_edge_mc(s->edge_emu_buffer, ptr, s->uvlinesize, 9, 9, src_x, src_y, h_edge_pos, v_edge_pos);
         ptr= s->edge_emu_buffer;
     }
-    pix_op[lowres](dest_cr, ptr, s->uvlinesize, block_s, sx, sy);
+    pix_op[op_index](dest_cr, ptr, s->uvlinesize, block_s, sx, sy);
 }
 
 /**