Re: [FFmpeg-devel] [PATCH 2/6] avcodec/ffwavesynth: Simplify lcg_seek(), avoid negative case

[Michael Niedermayer]

On Sat, Jun 22, 2019 at 01:29:32AM +0200, Michael Niedermayer wrote:
> Fixes: negation of -9223372036854775808 cannot be represented in type 
> 'int64_t' (aka 'long'); cast to an unsigned type to negate this value to 
> itself
> Fixes: 
> 15289/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFWAVESYNTH_fuzzer-5709034499342336
> 
> Found-by: continuous fuzzing process 
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer 
> ---
>  libavcodec/ffwavesynth.c | 12 +++-
>  1 file changed, 3 insertions(+), 9 deletions(-)


will apply

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

Frequently ignored answer#1 FFmpeg bugs should be sent to our bugtracker. User
questions about the command line tools should be sent to the ffmpeg-user ML.
And questions about how to use libav* should be sent to the libav-user ML.


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[FFmpeg-devel] [PATCH 2/6] avcodec/ffwavesynth: Simplify lcg_seek(), avoid negative case

[Michael Niedermayer]

Fixes: negation of -9223372036854775808 cannot be represented in type 'int64_t' 
(aka 'long'); cast to an unsigned type to negate this value to itself
Fixes: 
15289/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFWAVESYNTH_fuzzer-5709034499342336

Found-by: continuous fuzzing process 
https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer 
---
 libavcodec/ffwavesynth.c | 12 +++-
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/libavcodec/ffwavesynth.c b/libavcodec/ffwavesynth.c
index cf8c780f3e..b2cc7c8fc1 100644
--- a/libavcodec/ffwavesynth.c
+++ b/libavcodec/ffwavesynth.c
@@ -113,18 +113,12 @@ static uint32_t lcg_next(uint32_t *s)
 return *s;
 }
 
-static void lcg_seek(uint32_t *s, int64_t dt)
+static void lcg_seek(uint32_t *s, uint32_t dt)
 {
 uint32_t a, c, t = *s;
 
-if (dt >= 0) {
-a = LCG_A;
-c = LCG_C;
-} else { /* coefficients for a step backward */
-a = LCG_AI;
-c = (uint32_t)(-LCG_AI * LCG_C);
-dt = -dt;
-}
+a = LCG_A;
+c = LCG_C;
 while (dt) {
 if (dt & 1)
 t = a * t + c;
-- 
2.22.0

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