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[FFmpeg-devel,2/2] avcodec/rv34: Simplify getting right VLC

Message ID 20201022102006.571413-2-andreas.rheinhardt@gmail.com
State Accepted
Commit 3a836f38f609940d883b8d8ed5e8a526e803da3c
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Series [FFmpeg-devel,1/2] avcodec/rv34: Don't needlessly copy VLC length and symbol arrays
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Commit Message

Andreas Rheinhardt Oct. 22, 2020, 10:20 a.m. UTC
For both RealVideo 3.0 as well as RealVideo 4.0 the VLC table to use
depends upon the slice's quantization parameter; these are coded on five
bits in the bitstream and are therefore in the range of 0..31; yet the
last element here is not valid and therefore the quantizer is clipped to
the range 0..30 to get the index. But this is unnecessary: One can just
add one element more to the relevant array to avoid the clipping.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
---
 libavcodec/rv34.c     | 6 ++++--
 libavcodec/rv34data.h | 8 ++++----
 2 files changed, 8 insertions(+), 6 deletions(-)
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Patch

diff --git a/libavcodec/rv34.c b/libavcodec/rv34.c
index d251c6817c..09fa962b2f 100644
--- a/libavcodec/rv34.c
+++ b/libavcodec/rv34.c
@@ -24,6 +24,7 @@ 
  * RV30/40 decoder common data
  */
 
+#include "libavutil/avassert.h"
 #include "libavutil/imgutils.h"
 #include "libavutil/internal.h"
 
@@ -339,8 +340,9 @@  static inline RV34VLC* choose_vlc_set(int quant, int mod, int type)
 {
     if(mod == 2 && quant < 19) quant += 10;
     else if(mod && quant < 26) quant += 5;
-    return type ? &inter_vlcs[rv34_quant_to_vlc_set[1][av_clip(quant, 0, 30)]]
-                : &intra_vlcs[rv34_quant_to_vlc_set[0][av_clip(quant, 0, 30)]];
+    av_assert2(quant >= 0 && quant < 32);
+    return type ? &inter_vlcs[rv34_quant_to_vlc_set[1][quant]]
+                : &intra_vlcs[rv34_quant_to_vlc_set[0][quant]];
 }
 
 /**
diff --git a/libavcodec/rv34data.h b/libavcodec/rv34data.h
index 4b2701fee6..32ecc395a8 100644
--- a/libavcodec/rv34data.h
+++ b/libavcodec/rv34data.h
@@ -90,13 +90,13 @@  static const uint16_t rv34_qscale_tab[32] = {
 
 /**
  * tables used to translate a quantizer value into a VLC set for decoding
- * The first table is used for intraframes.
+ * The first table is used for intraframes. The two last entries are invalid.
  */
-static const uint8_t rv34_quant_to_vlc_set[2][31] = {
+static const uint8_t rv34_quant_to_vlc_set[2][32] = {
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1,
-   2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 0 },
+   2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3,
-   3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6 },
+   3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 6 },
 };
 
 /**