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

[Robert Swain]

2009/2/23 Michael Niedermayer <michaelni at gmx.at>:
> 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
>>
>> 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

Are you saying that we mandate IEEE754 compliant float arithmetic for
using FFmpeg so the #ifdefs are not necessary? If so, if Alex (or
someone) removes these, can the patch be applied?

Regards,
Rob