[FFmpeg-devel] LIBMPEG2_BITSTREAM_READER vs. golomb.h

[Michael Niedermayer]

On Mon, Jul 14, 2008 at 12:02:47AM +0100, M?ns Rullg?rd wrote:
> I just spent some time bug-hunting, only to discover that the
> exp-golomb functions in golomb.h do not work with
> LIBMPEG2_BITSTREAM_READER.  This is because they rely on more than the
> promised 17 bits to be available after an UPDATE_CACHE() call.
> 
> To avoid future mishaps, I was thinking of adding a preprocessor check
> to golomb.h (I'm too lazy to try to make it work). 

try:
@@ -64,10 +63,12 @@
 
         return ff_ue_golomb_vlc_code[buf];
     }else{
-        log= 2*av_log2(buf) - 31;
-        buf>>= log;
+        log= 31 - av_log2(buf);
+        LAST_SKIP_BITS(re, gb, log);
+        UPDATE_CACHE(re, gb);
+        buf= SHOW_UBITS(re, gb, log+1);
         buf--;
-        LAST_SKIP_BITS(re, gb, 32 - log);
+        LAST_SKIP_BITS(re, gb, log+1);
         CLOSE_READER(re, gb);
 
         return buf;
@@ -149,10 +150,11 @@
 
         return ff_se_golomb_vlc_code[buf];
     }else{
-        log= 2*av_log2(buf) - 31;
-        buf>>= log;
-
-        LAST_SKIP_BITS(re, gb, 32 - log);
+        log= 31 - av_log2(buf);
+        LAST_SKIP_BITS(re, gb, log);
+        UPDATE_CACHE(re, gb);
+        buf= SHOW_UBITS(re, gb, log+1);
+        LAST_SKIP_BITS(re, gb, log+1);
         CLOSE_READER(re, gb);
 
         if(buf&1) buf= -(buf>>1);


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many things microsoft did are stupid, but not doing something just because
microsoft did it is even more stupid. If everything ms did were stupid they
would be bankrupt already.
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