Correct chroma vector calculation for RealVideo 3.

Old version divided it wrong, which resulted in chroma drift (visible on FATE
sample too as dirty trails left by clouds).

Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavcodec/rv34.c

@@ -737,8 +737,8 @@ static inline void rv34_mc(RV34DecContext *r, const int block_type,
         my = (s->current_picture_ptr->f.motion_val[dir][mv_pos][1] + (3 << 24)) / 3 - (1 << 24);
         lx = (s->current_picture_ptr->f.motion_val[dir][mv_pos][0] + (3 << 24)) % 3;
         ly = (s->current_picture_ptr->f.motion_val[dir][mv_pos][1] + (3 << 24)) % 3;
-        chroma_mx = (s->current_picture_ptr->f.motion_val[dir][mv_pos][0] + 1) >> 1;
-        chroma_my = (s->current_picture_ptr->f.motion_val[dir][mv_pos][1] + 1) >> 1;
+        chroma_mx = s->current_picture_ptr->f.motion_val[dir][mv_pos][0] / 2;
+        chroma_my = s->current_picture_ptr->f.motion_val[dir][mv_pos][1] / 2;
         umx = (chroma_mx + (3 << 24)) / 3 - (1 << 24);
         umy = (chroma_my + (3 << 24)) / 3 - (1 << 24);
         uvmx = chroma_coeffs[(chroma_mx + (3 << 24)) % 3];

tests/ref/fate/rv30

@@ -16,31 +16,31 @@
 0, 112500, 126720, 0xe572dfc9
 0, 120000, 126720, 0xbc3cc34f
 0, 127500, 126720, 0xcf8cb0e2
-0, 135000, 126720, 0x6d1c630d
-0, 142500, 126720, 0x4338e469
-0, 150000, 126720, 0x9d82ea38
-0, 157500, 126720, 0x55e0b559
-0, 165000, 126720, 0x5eefb5ef
-0, 172500, 126720, 0x4b10b746
-0, 180000, 126720, 0x8b07a1db
-0, 187500, 126720, 0x8c639b34
-0, 195000, 126720, 0x63eb0b9f
-0, 202500, 126720, 0x31c80c83
-0, 210000, 126720, 0x78495352
-0, 217500, 126720, 0x63d609c4
-0, 225000, 126720, 0xcd2a62d8
-0, 232500, 126720, 0x4aea732d
-0, 240000, 126720, 0xe3bb352c
-0, 247500, 126720, 0x4b9036ad
-0, 255000, 126720, 0x88b66e2d
-0, 262500, 126720, 0x4a8a1b16
-0, 270000, 126720, 0x2e014eac
-0, 277500, 126720, 0x83212c67
-0, 285000, 126720, 0x4937e897
-0, 292500, 126720, 0x2d38babe
-0, 300000, 126720, 0xbcb43c09
-0, 307500, 126720, 0x955ffaf4
-0, 315000, 126720, 0x3337d4a2
-0, 322500, 126720, 0xe8f58c33
-0, 330000, 126720, 0x3a7f771f
-0, 337500, 126720, 0xb67c39b9
+0, 135000, 126720, 0x75ae61b6
+0, 142500, 126720, 0x554fe3e4
+0, 150000, 126720, 0x72ecea95
+0, 157500, 126720, 0x5d00b5fe
+0, 165000, 126720, 0xe39bba0d
+0, 172500, 126720, 0x9c21bad8
+0, 180000, 126720, 0x72f2a47d
+0, 187500, 126720, 0x4f639ebe
+0, 195000, 126720, 0x534a10cc
+0, 202500, 126720, 0xfdca11d3
+0, 210000, 126720, 0x0c735615
+0, 217500, 126720, 0x0eaf0c1b
+0, 225000, 126720, 0xce5e6794
+0, 232500, 126720, 0x14cf7974
+0, 240000, 126720, 0xbc513f2a
+0, 247500, 126720, 0xbc303fae
+0, 255000, 126720, 0xd9f67585
+0, 262500, 126720, 0x3378251f
+0, 270000, 126720, 0xb3ed5911
+0, 277500, 126720, 0xc15a3577
+0, 285000, 126720, 0x0a24f256
+0, 292500, 126720, 0xfab9c45d
+0, 300000, 126720, 0x45464610
+0, 307500, 126720, 0xfe2e057d
+0, 315000, 126720, 0x23efdc35
+0, 322500, 126720, 0x4d888b2e
+0, 330000, 126720, 0xdd0d74df
+0, 337500, 126720, 0x08382b8e