avcodec/clearvideo: Avoid huge VLC length tables

After the motion vector and bias values tables have been reordered so
that the codes are ordered from left to right, it emerged that the
length of these entries are actually ascending for every table.
Therefore it is possible to encode them in a run-length style and create
the actual length tables during runtime. This commit implements this.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1 files changed, 27 insertions, 7 deletions

diff --git a/libavcodec/clearvideo.c b/libavcodec/clearvideo.c
index f1dcb03f0e..39e3991053 100644
--- a/libavcodec/clearvideo.c
+++ b/libavcodec/clearvideo.c
@@ -646,9 +646,31 @@ static int clv_decode_frame(AVCodecContext *avctx, void *data,
     return mb_ret < 0 ? mb_ret : buf_size;
 }
 
+static av_cold int build_vlc(VLC *vlc, const uint8_t counts[16],
+                             const uint16_t **syms)
+{
+    uint8_t lens[MAX_VLC_ENTRIES];
+    unsigned num = 0;
+    int ret;
+
+    for (int i = 0; i < 16; i++) {
+        unsigned count = counts[i];
+        if (count == 255) /* Special case for Y_3 table */
+            count = 303;
+        for (count += num; num < count; num++)
+            lens[num] = i + 1;
+    }
+    ret = ff_init_vlc_from_lengths(vlc, 9, num, lens, 1, *syms, 2, 2, 0, 0, NULL);
+    if (ret < 0)
+        return ret;
+    *syms += num;
+    return 0;
+}
+
 static av_cold int clv_decode_init(AVCodecContext *avctx)
 {
     CLVContext *const c = avctx->priv_data;
+    const uint16_t *mv_syms = clv_mv_syms, *bias_syms = clv_bias_syms;
     int ret, w, h;
 
     if (avctx->extradata_size == 110) {
@@ -704,14 +726,13 @@ static av_cold int clv_decode_init(AVCodecContext *avctx)
         return ret;
     }
 
-    for (int i = 0, j = 0;; i++) {
+    for (int i = 0, j = 0, k = 0;; i++) {
         if (0x36F & (1 << i)) {
             c->lev[i].mv_esc = clv_mv_escape[i];
-            ret = ff_init_vlc_from_lengths(&c->lev[i].mv_cb, 9, clv_mv_sizes[i],
-                                           clv_mv_bits[i], 1,
-                                           clv_mv_syms[i], 2, 2, 0, 0, avctx);
+            ret = build_vlc(&c->lev[i].mv_cb, clv_mv_len_counts[k], &mv_syms);
             if (ret < 0)
                 return ret;
+            k++;
         }
         if (i == FF_ARRAY_ELEMS(c->lev) - 1)
             break;
@@ -723,9 +744,8 @@ static av_cold int clv_decode_init(AVCodecContext *avctx)
                 return ret;
 
             c->lev[i + 1].bias_esc = 0x100;
-            ret = ff_init_vlc_from_lengths(&c->lev[i + 1].bias_cb, 9, clv_bias_sizes[j],
-                                           clv_bias_bits[j], 1,
-                                           clv_bias_syms[j], 2, 2, 0, 0, avctx);
+            ret = build_vlc(&c->lev[i + 1].bias_cb,
+                            clv_bias_len_counts[j], &bias_syms);
             if (ret < 0)
                 return ret;
             j++;