[FFmpeg-devel] [PATCH] AAC: type puns for 16 bit floating point rounding

[Michael Niedermayer]

On Sun, Feb 22, 2009 at 05:51:58PM -0500, Alex Converse wrote:
> On Mon, Feb 16, 2009 at 7:22 PM, Alex Converse <alex.converse at gmail.com> wrote:
> > On Thu, Feb 12, 2009 at 9:29 AM, Robert Swain <robert.swain at gmail.com> wrote:
> >> 2008/12/21 Robert Swain <robert.swain at gmail.com>:
> >>> 2008/12/13 Guillaume POIRIER <poirierg at gmail.com>:
> >>>> On Sat, Dec 13, 2008 at 3:54 PM, M?ns Rullg?rd <mans at mansr.com> wrote:
> >>>>> Can you upload the file somewhere?  I'd rather not install mp4box just
> >>>>> for this.
> >>>>
> >>>> Sure, here it is: http://natsuki.mplayerhq.hu/~ml-admin/type_puns.mp4
> >>>
> >>> M?ns?
> >>
> >> This thread seems to be mostly dead. Maybe Alex can do something to
> >> make the speed testing that needs to be done easier so we can get
> >> these optimisations merged into trunk, if indeed they do make decoding
> >> faster.
> >>
> >
> > /MPlayer/incoming/aac-main/aac-main-long.adts,txt
> >
> > My system reports (Linux/amd64):
> > before:
> > real    0m7.602s
> > user    0m7.568s
> > sys     0m0.032s
> >
> > after:
> > real    0m1.182s
> > user    0m1.148s
> > sys     0m0.040s
> >
> > I think we are looking for someone on ARM to test
> >
> > Regards,
> > Alex Converse
> >
> 
> Let's try this one more time:
> 
> We are looking for people on exotic architectures (non-x86) to
> benchmark decoding a specific file on their systems before and after
> the attached patch.
> 
> The file: /MPlayer/incoming/aac-main/aac-main-long.adts,txt
> Mirror: http://filer.case.edu/ajc30/pub/ffmpeg/
> 
> Thanks,
> Alex Converse

[...]
> @@ -871,24 +875,45 @@ static int decode_spectrum_and_dequant(AACContext * ac, float coef[1024], GetBit
>  }
>  
>  static av_always_inline float flt16_round(float pf) {
> +#ifdef HAVE_IEEE754_PUN
> +    union float754 tmp;
> +    tmp.f = pf;
> +    tmp.i = (tmp.i + 0x00008000U) & 0xFFFF0000U;
> +    return tmp.f;
> +#else
>      int exp;
>      pf = frexpf(pf, &exp);
>      pf = ldexpf(roundf(ldexpf(pf, 8)), exp-8);
>      return pf;
> +#endif
>  }
>  

what is the point of the silly redundancy?
I would replace the old code by the new, not keep both with #ifdefs
thats not good for readability.
Of course thats unless you do find a system where the frexpf()/ldexpf is
faster but i doubt such system exists


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I wish the Xiph folks would stop pretending they've got something they
do not.  Somehow I fear this will remain a wish. -- M?ns Rullg?rd
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