[FFmpeg-devel] [PATCH 3/7] avutil/common: Implement av_sat_add64_c() with fewer branches

[Michael Niedermayer]

On Wed, Oct 21, 2020 at 12:17:41PM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > No benchmark because this is not used in any speed relevant pathes nor is it
> > used where __builtin_add_overflow is available.
> > So I do not know how to realistically benchmark it.
> > 
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavutil/common.h | 9 ++++-----
> >  1 file changed, 4 insertions(+), 5 deletions(-)
> > 
> > diff --git a/libavutil/common.h b/libavutil/common.h
> > index 92b721a59c..a48c0648f8 100644
> > --- a/libavutil/common.h
> > +++ b/libavutil/common.h
> > @@ -303,11 +303,10 @@ static av_always_inline int64_t av_sat_add64_c(int64_t a, int64_t b) {
> >      int64_t tmp;
> >      return !__builtin_add_overflow(a, b, &tmp) ? tmp : (tmp < 0 ? INT64_MAX : INT64_MIN);
> >  #else
> > -    if (b >= 0 && a >= INT64_MAX - b)
> > -        return INT64_MAX;
> > -    if (b <= 0 && a <= INT64_MIN - b)
> > -        return INT64_MIN;
> > -    return a + b;
> > +    int64_t s = a+(uint64_t)b;
> > +    if ((int64_t)(a^b | ~s^b) >= 0)
> > +        return b < 0 ? INT64_MIN : INT64_MAX;
> > +    return s;
> >  #endif
> >  }
> >  
> > 
> Returning INT64_MAX ^ (b >> 63) would have even less branches

will do that in case noone objects to the patch itself

[...]

thx
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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people, be surprised about them taking revenge and drop even more bombs
and strip your own citizens of their rights and freedoms. to be continued
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