[FFmpeg-devel] [PATCH 07/12] WMA: use fill_float from dsputil

[Michael Niedermayer]

On Sun, Sep 27, 2009 at 11:49:38PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> 
> > On Sun, Sep 27, 2009 at 11:49:23AM +0100, Mans Rullgard wrote:
> >> ---
> >>  libavcodec/wmadec.c |   11 +++++------
> >>  1 files changed, 5 insertions(+), 6 deletions(-)
> >> 
> >> diff --git a/libavcodec/wmadec.c b/libavcodec/wmadec.c
> >> index e5f0508..52ea7a3 100644
> >> --- a/libavcodec/wmadec.c
> >> +++ b/libavcodec/wmadec.c
> >> @@ -262,9 +262,8 @@ static int decode_exp_vlc(WMACodecContext *s, int ch)
> >>          v = pow(10, last_exp * (1.0 / 16.0));
> >>          max_scale = v;
> >>          n = *ptr++;
> >> -        do {
> >> -            *q++ = v;
> >> -        } while (--n);
> >> +        s->dsp.fill_float(q, v, n);
> >> +        q += n;
> >>      }else
> >>          last_exp = 36;
> >>  
> >> @@ -275,13 +274,13 @@ static int decode_exp_vlc(WMACodecContext *s, int ch)
> >>          /* NOTE: this offset is the same as MPEG4 AAC ! */
> >>          last_exp += code - 60;
> >>          /* XXX: use a table */
> >> +        av_log(NULL, AV_LOG_ERROR, "exp= %d\n", last_exp);
> >>          v = pow(10, last_exp * (1.0 / 16.0));
> >>          if (v > max_scale)
> >>              max_scale = v;
> >>          n = *ptr++;
> >> -        do {
> >> -            *q++ = v;
> >> -        } while (--n);
> >> +        s->dsp.fill_float(q, v, n);
> >> +        q += n;
> >>      }
> >
> > the call overhead should be quite significant here,
> 
> I wouldn't have done this if there wasn't a substantial performance
> benefit.  I don't remember how much this change gave, but it was huge,
> meaning at least 10% in overall decoding speed.  GCC really is that
> stupid.
> 
> Since I replaced that pow() call with a table lookup in the next
> patch, it would be trivial to replace that with some int* casts, thus
> subverting gcc's pessimiser.  Would you be happier with this approach?

yes


[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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