[FFmpeg-devel] [PATCH 3/4] avcodec/get_bits: Implement get_vlc_multi()

[Michael Niedermayer <michael@niedermayer.cc>]

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/get_bits.h | 61 ++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 58 insertions(+), 3 deletions(-)

diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index 86cea00494a..806e4b16f49 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -668,13 +668,68 @@ static av_always_inline int get_vlc2(GetBitContext *s, const VLCElem *table,
     return code;
 }
 
-static inline int get_vlc_multi(GetBitContext *s, uint8_t *dst,
+/**
+ * Parse a vlc / vlc_multi code.
+ * @param bits is the number of bits which will be read at once, must be
+ *             identical to nb_bits in vlc_init(), should be known at compile time
+ * @param max_depth is the number of times bits bits must be read to completely
+ *                  read the longest vlc code
+ *                  = (max_vlc_length + bits - 1) / bits
+ * @param dst the parsed symbol(s) will be stored here. Up to 8 bytes are written
+ * @returns number of symbols parsed
+ * If the vlc code is invalid and max_depth=1, then no bits will be removed.
+ * If the vlc code is invalid and max_depth>1, then the number of bits removed
+ * is undefined.
+ */
+static inline int get_vlc_multi(GetBitContext *s,  uint8_t * restrict dst,
                                 const VLC_MULTI_ELEM *const Jtable,
                                 const VLCElem *const table,
                                 const int bits, const int max_depth)
 {
-    dst[0] = get_vlc2(s, table, bits, max_depth);
-    return 1;
+    int ret, nb_bits, n;
+    unsigned int index;
+
+    OPEN_READER(re, s);
+    UPDATE_CACHE(re, s);
+
+    index = SHOW_UBITS(re, s, bits);
+    n = Jtable[index].len;
+    if (Jtable[index].num) {
+        AV_COPY64U(dst, Jtable[index].val);
+        ret = Jtable[index].num;
+    } else {
+        int code = table[index].sym;
+
+        if (av_builtin_constant_p(bits <= MIN_CACHE_BITS/2) && bits <= MIN_CACHE_BITS/2) {
+            SKIP_BITS(re, s, bits);
+        } else {
+            LAST_SKIP_BITS(re, s, bits);
+            UPDATE_CACHE(re, s);
+        }
+
+        nb_bits = -n;
+
+        index = SHOW_UBITS(re, s, nb_bits) + code;
+        code  = table[index].sym;
+        n     = table[index].len;
+        if (max_depth > 2 && n < 0) {
+            LAST_SKIP_BITS(re, s, nb_bits);
+            UPDATE_CACHE(re, s);
+
+            nb_bits = -n;
+
+            index = SHOW_UBITS(re, s, nb_bits) + code;
+            code  = table[index].sym;
+            n     = table[index].len;
+        }
+        dst[0] = code;
+        ret = n > 0;
+    }
+    LAST_SKIP_BITS(re, s, n);
+
+    CLOSE_READER(re, s);
+
+    return ret;
 }
 
 static inline int decode012(GetBitContext *gb)
-- 
2.17.1

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