[FFmpeg-cvslog] avcodec/pixlet: Simplify nbits computation

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Wed Jul 26 20:10:28 2017 +0200| [aeddb3607be94b1d6fef41b602b07f08223ea565] | committer: Michael Niedermayer

avcodec/pixlet: Simplify nbits computation

Fixes multiple integer overflows
Fixes: runtime error: signed integer overflow: 1 + 2147483647 cannot be represented in type 'int'

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda at gmail.com>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=aeddb3607be94b1d6fef41b602b07f08223ea565
---

 libavcodec/pixlet.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/pixlet.c b/libavcodec/pixlet.c
index 0e541a9ccb..a9661d3ab6 100644
--- a/libavcodec/pixlet.c
+++ b/libavcodec/pixlet.c
@@ -206,8 +206,8 @@ static int read_high_coeffs(AVCodecContext *avctx, uint8_t *src, int16_t *dst, i
     if ((ret = init_get_bits8(b, src, bytestream2_get_bytes_left(&ctx->gb))) < 0)
       return ret;
 
-    if ((a >= 0) + (a ^ (a >> 31)) - (a >> 31) != 1) {
-        nbits = 33 - ff_clz((a >= 0) + (a ^ (a >> 31)) - (a >> 31) - 1);
+    if (a ^ (a >> 31)) {
+        nbits = 33 - ff_clz(a ^ (a >> 31));
         if (nbits > 16)
             return AVERROR_INVALIDDATA;
     } else {