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mathops: remove undefined behaviour from sign_extend()

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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>
This commit is contained in:
Mans Rullgard 2011-10-09 12:57:08 +01:00
parent 42feaf4070
commit f59bb3d8f3
1 changed files with 3 additions and 1 deletions
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libavcodec/mathops.h
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@ -116,7 +116,9 @@ static inline av_const int mid_pred(int a, int b, int c)
#ifndef sign_extend #ifndef sign_extend
static inline av_const int sign_extend(int val, unsigned bits) 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 #endif