avcodec/vp3: Apply VLC offset during init

By switching to ff_init_vlc_from_lengths() one can apply both positive
as well as negative offsets for free; in this case it even saves space
because one replaces codes tables that don't fit into an uint8_t by
symbols tables that fit into an uint8_t or can even be completely
avoided as they are trivial.
Signed-off-by: NAndreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/vp3.c

@@ -48,6 +48,9 @@
 #include "vp3dsp.h"
 #include "xiph.h"
 
+#define VP4_MV_VLC_BITS     6
+#define SUPERBLOCK_VLC_BITS 6
+
 #define FRAGMENT_PIXELS 8
 
 // FIXME split things out into their own arrays
@@ -489,7 +492,7 @@ static int unpack_superblocks(Vp3DecodeContext *s, GetBitContext *gb)
                 bit ^= 1;
 
             current_run = get_vlc2(gb, s->superblock_run_length_vlc.table,
-                                   6, 2) + 1;
+                                   SUPERBLOCK_VLC_BITS, 2);
             if (current_run == 34)
                 current_run += get_bits(gb, 12);
 
@@ -523,7 +526,7 @@ static int unpack_superblocks(Vp3DecodeContext *s, GetBitContext *gb)
                     bit ^= 1;
 
                 current_run = get_vlc2(gb, s->superblock_run_length_vlc.table,
-                                       6, 2) + 1;
+                                       SUPERBLOCK_VLC_BITS, 2);
                 if (current_run == 34)
                     current_run += get_bits(gb, 12);
 
@@ -885,7 +888,8 @@ static int unpack_modes(Vp3DecodeContext *s, GetBitContext *gb)
 
 static int vp4_get_mv(Vp3DecodeContext *s, GetBitContext *gb, int axis, int last_motion)
 {
-    int v = get_vlc2(gb, s->vp4_mv_vlc[axis][vp4_mv_table_selector[FFABS(last_motion)]].table, 6, 2) - 31;
+    int v = get_vlc2(gb, s->vp4_mv_vlc[axis][vp4_mv_table_selector[FFABS(last_motion)]].table,
+                     VP4_MV_VLC_BITS, 2);
     return last_motion < 0 ? -v : v;
 }
 
@@ -1104,7 +1108,8 @@ static int unpack_block_qpis(Vp3DecodeContext *s, GetBitContext *gb)
             else
                 bit ^= 1;
 
-            run_length = get_vlc2(gb, s->superblock_run_length_vlc.table, 6, 2) + 1;
+            run_length = get_vlc2(gb, s->superblock_run_length_vlc.table,
+                                  SUPERBLOCK_VLC_BITS, 2);
             if (run_length == 34)
                 run_length += get_bits(gb, 12);
             blocks_decoded += run_length;
@@ -2452,9 +2457,10 @@ static av_cold int vp3_decode_init(AVCodecContext *avctx)
         }
     }
 
-    if ((ret = init_vlc(&s->superblock_run_length_vlc, 6, 34,
-                        &superblock_run_length_vlc_table[0][1], 4, 2,
-                        &superblock_run_length_vlc_table[0][0], 4, 2, 0)) < 0)
+    ret = ff_init_vlc_from_lengths(&s->superblock_run_length_vlc, SUPERBLOCK_VLC_BITS, 34,
+                                   superblock_run_length_vlc_lens, 1,
+                                   NULL, 0, 0, 1, 0, avctx);
+    if (ret < 0)
         return ret;
 
     if ((ret = init_vlc(&s->fragment_run_length_vlc, 5, 30,
@@ -2474,11 +2480,14 @@ static av_cold int vp3_decode_init(AVCodecContext *avctx)
 
 #if CONFIG_VP4_DECODER
     for (j = 0; j < 2; j++)
-        for (i = 0; i < 7; i++)
-            if ((ret = init_vlc(&s->vp4_mv_vlc[j][i], 6, 63,
-                                &vp4_mv_vlc[j][i][0][1], 4, 2,
-                                &vp4_mv_vlc[j][i][0][0], 4, 2, 0)) < 0)
+        for (i = 0; i < 7; i++) {
+            ret = ff_init_vlc_from_lengths(&s->vp4_mv_vlc[j][i], VP4_MV_VLC_BITS, 63,
+                                           &vp4_mv_vlc[j][i][0][1], 2,
+                                           &vp4_mv_vlc[j][i][0][0], 2, 1, -31,
+                                           0, avctx);
+            if (ret < 0)
                 return ret;
+        }
 
     /* version >= 2 */
     for (i = 0; i < 2; i++)

libavcodec/vp3data.h

@@ -95,25 +95,11 @@ static const uint8_t vp31_filter_limit_values[64] = {
      0,  0,  0,  0,  0,  0,  0,  0
 };
 
-static const uint16_t superblock_run_length_vlc_table[34][2] = {
-    {     0,  1 },
-
-    {     4,  3 }, {     5,  3 },
-
-    {   0xC,  4 }, {   0xD,  4 },
-
-    {  0x38,  6 }, {  0x39,  6 }, {  0x3A,  6 }, {  0x3B,  6 },
-
-    {  0xF0,  8 }, {  0xF1,  8 }, {  0xF2,  8 }, {  0xF3,  8 },
-    {  0xF4,  8 }, {  0xF5,  8 }, {  0xF6,  8 }, {  0xF7,  8 },
-
-    { 0x3E0, 10 }, { 0x3E1, 10 }, { 0x3E2, 10 }, { 0x3E3, 10 },
-    { 0x3E4, 10 }, { 0x3E5, 10 }, { 0x3E6, 10 }, { 0x3E7, 10 },
-    { 0x3E8, 10 }, { 0x3E9, 10 }, { 0x3EA, 10 }, { 0x3EB, 10 },
-    { 0x3EC, 10 }, { 0x3ED, 10 }, { 0x3EE, 10 }, { 0x3EF, 10 },
-
-    {  0x3F,  6 } /* this last VLC is a special case for reading 12 more
-                   * bits from stream and adding the value 34 */
+static const uint8_t superblock_run_length_vlc_lens[34] = {
+     1,  3,  3,  4,  4,  6,  6,  6,  6,  8,  8,  8,  8,  8,  8,  8,  8, 10, 10,
+    10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
+     6, /* This last value is a special case for reading 12 more
+         * bits from the stream and adding the value 34. */
 };
 
 static const uint16_t fragment_run_length_vlc_table[30][2] = {