From 2e7800778c8aadb3362797caca4b6daa8c6bf3a0 Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michael@niedermayer.cc>
Date: Sat, 3 Dec 2016 23:44:56 +0100
Subject: [PATCH] avcodec/get_bits: Fix get_sbits_long(0)

Fixes undefined behavior
Fixes: 640889-media

Found-by: Matt Wolenetz <wolenetz@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit c72fa432349881d5a445cd110abf698cc94d490d)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/get_bits.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index b9dec4fe35..8a40aeeae7 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -374,6 +374,10 @@ static inline uint64_t get_bits64(GetBitContext *s, int n)
  */
 static inline int get_sbits_long(GetBitContext *s, int n)
 {
+    // sign_extend(x, 0) is undefined
+    if (!n)
+        return 0;
+
     return sign_extend(get_bits_long(s, n), n);
 }