From f59bb3d8f3eb50aa182b0d7ae209848b94a507cc Mon Sep 17 00:00:00 2001
From: Mans Rullgard <mans@mansr.com>
Date: Sun, 9 Oct 2011 12:57:08 +0100
Subject: [PATCH] mathops: remove undefined behaviour from sign_extend()
This function intentionally overflows the signed range on
the left shift. Using this type-punning avoids errors from
the overflow checker without disabling this test globally.
Signed-off-by: Mans Rullgard <mans@mansr.com>
---
libavcodec/mathops.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/libavcodec/mathops.h b/libavcodec/mathops.h
index ec76eaae291..45b1ecf1ae4 100644
--- a/libavcodec/mathops.h
+++ b/libavcodec/mathops.h
@@ -116,7 +116,9 @@ static inline av_const int mid_pred(int a, int b, int c)
#ifndef sign_extend
static inline av_const int sign_extend(int val, unsigned bits)
{
- return (val << ((8 * sizeof(int)) - bits)) >> ((8 * sizeof(int)) - bits);
+ unsigned shift = 8 * sizeof(int) - bits;
+ union { unsigned u; int s; } v = { (unsigned) val << shift };
+ return v.s >> shift;
}
#endif
--
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