[FFmpeg-cvslog] avcodec/vlc, bitstream: Fix multi VLC with uint8_t syms on BE

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Sat Mar 30 03:25:24 2024 +0100| [4ab82d2fb6361864521b41a5c8168902e534fa1a] | committer: Andreas Rheinhardt

avcodec/vlc, bitstream: Fix multi VLC with uint8_t syms on BE

VLC_MULTI_ELEM contains an uint8_t array that is supposed
to be treated as an array of uint16_t when the used symbols
have a size of two; otherwise it should be treated as just
an array of uint8_t, but it was not always treated that way:

vlc_multi_gen() initialized the first entry of the array
by writing the symbol via AV_WN16; on big endian systems,
the intended value was instead written into the second entry
of the array (where it would likely be overwritten lateron
during initialization).

read_vlc_multi() also treated this case incorrectly: In case
the code is so long that it needs a classical multi-stage lookup,
the symbol has been written to the destination as if via AV_WN16.
On little endian systems, this sets the correct first symbol and
clobbers (zeroes) the next one, but the next one will be overwritten
lateron anyway, so it won't be recognized. But on big-endian systems,
the first symbol will be set to zero and the actually read symbol
will be put into the slot for the next one (where it will be overwritten
lateron).

This commit fixes this; this fixes the magicyuv and utvideo FATE-tests
on big endian arches.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=4ab82d2fb6361864521b41a5c8168902e534fa1a
---

 libavcodec/bitstream_template.h | 8 ++++++--
 libavcodec/get_bits.h           | 3 ++-
 libavcodec/magicyuv.c           | 2 +-
 libavcodec/utvideodec.c         | 2 +-
 libavcodec/vlc.c                | 5 ++++-
 5 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/libavcodec/bitstream_template.h b/libavcodec/bitstream_template.h
index 4f3d07275f..c8e4a5131e 100644
--- a/libavcodec/bitstream_template.h
+++ b/libavcodec/bitstream_template.h
@@ -536,7 +536,8 @@ static inline int BS_FUNC(read_vlc)(BSCTX *bc, const VLCElem *table,
 static inline int BS_FUNC(read_vlc_multi)(BSCTX *bc, uint8_t dst[8],
                                           const VLC_MULTI_ELEM *const Jtable,
                                           const VLCElem *const table,
-                                          const int bits, const int max_depth)
+                                          const int bits, const int max_depth,
+                                          const int symbols_size)
 {
     unsigned idx = BS_FUNC(peek)(bc, bits);
     int ret, nb_bits, code, n = Jtable[idx].len;
@@ -554,7 +555,10 @@ static inline int BS_FUNC(read_vlc_multi)(BSCTX *bc, uint8_t dst[8],
                 code = BS_FUNC(priv_set_idx)(bc, code, &n, &nb_bits, table);
             }
         }
-        AV_WN16(dst, code);
+        if (symbols_size == 1)
+            *dst = code;
+        else
+            AV_WN16(dst, code);
         ret = n > 0;
     }
     BS_FUNC(priv_skip_remaining)(bc, n);
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index cfcf97c021..fe2f6378b4 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -667,7 +667,8 @@ static av_always_inline int get_vlc2(GetBitContext *s, const VLCElem *table,
 static inline int get_vlc_multi(GetBitContext *s, uint8_t *dst,
                                 const VLC_MULTI_ELEM *const Jtable,
                                 const VLCElem *const table,
-                                const int bits, const int max_depth)
+                                const int bits, const int max_depth,
+                                const int symbols_size)
 {
     dst[0] = get_vlc2(s, table, bits, max_depth);
     return 1;
diff --git a/libavcodec/magicyuv.c b/libavcodec/magicyuv.c
index d2897019bd..06fad8f3f7 100644
--- a/libavcodec/magicyuv.c
+++ b/libavcodec/magicyuv.c
@@ -125,7 +125,7 @@ static void magicyuv_median_pred16(uint16_t *dst, const uint16_t *src1,
     x = 0; \
     for (; CACHED_BITSTREAM_READER && x < width-c && get_bits_left(&gb) > 0;) {\
         ret = get_vlc_multi(&gb, (uint8_t *)dst + x * b, multi, \
-                            vlc, vlc_bits, 3); \
+                            vlc, vlc_bits, 3, b); \
         if (ret <= 0) \
             return AVERROR_INVALIDDATA; \
         x += ret; \
diff --git a/libavcodec/utvideodec.c b/libavcodec/utvideodec.c
index 49e34cc90a..5377926fa6 100644
--- a/libavcodec/utvideodec.c
+++ b/libavcodec/utvideodec.c
@@ -121,7 +121,7 @@ static int build_huff(UtvideoContext *c, const uint8_t *src, VLC *vlc,
     i = 0; \
     for (; CACHED_BITSTREAM_READER && i < width-end && get_bits_left(&gb) > 0;) {\
         ret = get_vlc_multi(&gb, (uint8_t *)buf + i * b, multi.table, \
-                            vlc.table, VLC_BITS, 3); \
+                            vlc.table, VLC_BITS, 3, b); \
         if (ret > 0) \
             i += ret; \
         if (ret <= 0) \
diff --git a/libavcodec/vlc.c b/libavcodec/vlc.c
index 78510e30d6..e01cc41689 100644
--- a/libavcodec/vlc.c
+++ b/libavcodec/vlc.c
@@ -499,7 +499,10 @@ static int vlc_multi_gen(VLC_MULTI_ELEM *table, const VLC *single,
     for (int j = 0; j < 1<<numbits; j++) {
         table[j].len = single->table[j].len;
         table[j].num = single->table[j].len > 0 ? 1 : 0;
-        AV_WN16(table[j].val, single->table[j].sym);
+        if (is16bit)
+            AV_WN16(table[j].val, single->table[j].sym);
+        else
+            table[j].val[0] = single->table[j].sym;
     }
 
     add_level(table, is16bit, nb_codes, numbits, buf,