[FFmpeg-cvslog] avcodec/pixlet: Fix log(0) check

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Sat Jun 13 11:21:52 2020 +0200| [17175055f84c181629e2ed9c394d4eed451f9925] | committer: Michael Niedermayer

avcodec/pixlet: Fix log(0) check

Fixes: passing zero to clz(), which is not a valid argument
Fixes: 23337/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PIXLET_fuzzer-5179131989065728

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit bd0f81526d3f4c23ecd0a399829103be2445c011)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=17175055f84c181629e2ed9c394d4eed451f9925
---

 libavcodec/pixlet.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/pixlet.c b/libavcodec/pixlet.c
index 03a2cdacc8..6cb6516227 100644
--- a/libavcodec/pixlet.c
+++ b/libavcodec/pixlet.c
@@ -221,7 +221,7 @@ static int read_high_coeffs(AVCodecContext *avctx, uint8_t *src, int16_t *dst,
     length = 25 - nbits;
 
     while (i < size) {
-        if (state >> 8 != -3)
+        if (((state >> 8) + 3) & 0xFFFFFFF)
             value = ff_clz((state >> 8) + 3) ^ 0x1F;
         else
             value = -1;