[FFmpeg-devel] [PATCH] atrac decoder

[Michael Niedermayer]

On Wed, Aug 12, 2009 at 10:13:51PM +0200, Benjamin Larsson wrote:
> M?ns Rullg?rd wrote:
> > Benjamin Larsson <banan at ludd.ltu.se> writes:
> > 
> >> Michael Niedermayer wrote:
> >>>> Well as vector_fmul_window is defined now you need to use the complete
> >>>> windows.
> >>> and when window is 0 or 1 some other function could be used, besides
> >>> is vector_fmul_window + half_imdct slower than the cutrrent code?
> >>>
> >> I did a test run that used one call to imdct_half and on call to
> >> vector_fmul_window per time the imdct function was invoked (ie it didn't
> >> decode properly it was just the same amount of calls). I got these numbers:
> >>
> >> mdct_regular
> >> 192195 dezicycles in mdct, 127 runs, 1 skips
> >> 190436 dezicycles in mdct, 255 runs, 1 skips
> >> 189578 dezicycles in mdct, 511 runs, 1 skips
> >> 190527 dezicycles in mdct, 1021 runs, 3 skips
> >> 190002 dezicycles in mdct, 2043 runs, 5 skips
> >> 188916 dezicycles in mdct, 4086 runs, 10 skips
> >> 188563 dezicycles in mdct, 8173 runs, 19 skips/s
> >>
> >> mdct_half
> >> 162004 dezicycles in mdct, 127 runs, 1 skips
> >> 161286 dezicycles in mdct, 255 runs, 1 skips
> >> 163959 dezicycles in mdct, 511 runs, 1 skips
> >> 164064 dezicycles in mdct, 1022 runs, 2 skips
> >> 163556 dezicycles in mdct, 2043 runs, 5 skips
> >> 163445 dezicycles in mdct, 4088 runs, 8 skipss/s
> >> 163775 dezicycles in mdct, 8180 runs, 12 skips/s
> >>
> >> Is that difference worth the extra memory needed for the mdct windows ?
> > 
> > That's a significant speedup.  How much memory are we talking about?
> > 
> 
> sizeof(float)*(128+256) bytes + some code to build the tables. And to
> reiterate the code using mdct_half and fmul_window didn't produce valid
> output, I just added the same amount of calls that would be needed for
> real output. So the values should be fairly accurate but would differ
> from a working implementation.

1.5kb is not much

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

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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