[FFmpeg-devel] [PATCH]HE-AACv1 try 3 (all missing functionality added)
Michael Niedermayer
michaelni
Sat Feb 13 20:04:55 CET 2010
On Sat, Feb 13, 2010 at 05:24:21PM +0000, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
>
> > On Sat, Feb 13, 2010 at 05:31:59PM +0100, Vitor Sessak wrote:
> > [...]
> >>> +
> >>> +static void vector_fmul_scalar_fadd_scalar_c(float *dst, const float
> >>> *src,
> >>> + float mul, float add, int
> >>> len)
> >>> +{
> >>> + int i;
> >>> + for (i = 0; i < len; i++)
> >>> + dst[i] = src[i] * mul + add;
> >>> +}
> >>> +
> >>
> >> Did you benchmark if hand-unrolling these loops give any benefit? You know
> >> that len is a multiple of four, but the compiler don't.
> >
> > assert(len>0 && len%4==0);
> > then the compiler knows it too :)
>
> Only if you compile with asserts enabled, which will slow things down
> immensely in code like this.
>
> > and after you looked at what gcc generates if forced to unroll
> > (theres a flag for that IIRC)
> > then post a code pessimization bug to the gcc-devels
> > -> only way to see gcc get better at these things
>
> What we need is a "soft assert" whereby we can tell the compiler
> things we know to be true without any code being generated for it.
> Some compilers have that already.
a preprocessor could turn an assert() when disabled into a "soft assert"
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway
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