On Fri, Jan 06, 2017 at 09:11:10PM -0300, James Almer wrote: > On 1/6/2017 4:46 PM, Andreas Cadhalpun wrote: > > Suggested-by: Rodger Combs <rodger.co...@gmail.com> > > Signed-off-by: Andreas Cadhalpun <andreas.cadhal...@googlemail.com> > > --- > > > > Changed the name as suggested by wm4 and the return value as suggested > > by Muhammad Faiz. > > There are also two new overflow checks at the end of the series. > > This is a good chance to introduce the gcc overflow check builtins. > See https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html, they > use hardware instructions when possible, like x86's Jump on Overflow. > > The idea would be to use __builtin_mul_overflow_p(). For example (untested): > > #if AV_GCC_VERSION_AT_LEAST(5,1) > #define av_builtin_mul_overflow_p(a, b) __builtin_mul_overflow_p(a, b, (int) > 0) > #else > #define av_builtin_mul_overflow_p(a, b) ((a) > INT_MAX / (b))) > #endif > > It can also be used all across the codebase, not just for these checks. >
> >
> > ---
> > libavutil/common.h | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/libavutil/common.h b/libavutil/common.h
> > index 8142b31fdb..6d795a353a 100644
> > --- a/libavutil/common.h
> > +++ b/libavutil/common.h
> > @@ -99,6 +99,8 @@
> > #define FFSWAP(type,a,b) do{type SWAP_tmp= b; b= a; a= SWAP_tmp;}while(0)
> > #define FF_ARRAY_ELEMS(a) (sizeof(a) / sizeof((a)[0]))
> >
> > +#define FF_RETURN_ON_OVERFLOW(ctx, x) if (x) {av_log(ctx, AV_LOG_ERROR,
> > "Overflow check failed: " #x"\n"); return AVERROR(ERANGE);}
>
> Printing an error unconditionally seems like log bloat. We do all kinds of
> sanity checks on demuxers and simply return INVALIDDATA without printing
> anything if they fail.
> Maybe we should do the same here and let the demuxer choose to print an
> error or not.
error messages help debuging and thus maintaining code.
[...]
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Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
If you drop bombs on a foreign country and kill a hundred thousand
innocent people, expect your government to call the consequence
"unprovoked inhuman terrorist attacks" and use it to justify dropping
more bombs and killing more people. The technology changed, the idea is old.
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