From 979572365f2133f969f3f49ec6a99cc8739d2eba Mon Sep 17 00:00:00 2001
From: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Date: Fri, 9 Oct 2015 15:59:04 -0400
Subject: [PATCH] avcodec/ac3enc: fix undefined negative left shift
This should fix the undefined behavior reported in:
https://trac.ffmpeg.org/ticket/4727.
I can reproduce this at runtime: simply stick in an abort call in
asym_quant to check if c < 0 and run FATE. I don't know ac3 so I can't
confirm if negative coefficients are intentional, but at the moment they
clearly are according to FATE.
This resolves the undefined behavior. Tested with FATE.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
libavcodec/ac3enc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c
index 35e721a964a..c8a0caa1949 100644
--- a/libavcodec/ac3enc.c
+++ b/libavcodec/ac3enc.c
@@ -1183,7 +1183,7 @@ static inline int asym_quant(int c, int e, int qbits)
{
int m;
- c = (((c << e) >> (24 - qbits)) + 1) >> 1;
+ c = (((c * (1<<e)) >> (24 - qbits)) + 1) >> 1;
m = (1 << (qbits-1));
if (c >= m)
c = m - 1;
--
GitLab