[FFmpeg-devel] [RFC] ac3dec: use dsputil.clear_block

Justin Ruggles justin.ruggles
Thu Jan 14 00:52:30 CET 2010

M?ns Rullg?rd wrote:

> Justin Ruggles <justin.ruggles at gmail.com> writes:
>> Reimar D?ffinger wrote:
>>> On Wed, Jan 13, 2010 at 11:42:27PM +0100, Michael Niedermayer wrote:
>>>> On Wed, Jan 13, 2010 at 09:46:17PM +0100, Reimar D?ffinger wrote:
>>>>> Hello,
>>>>> this gives an overall speedup of about 1.1 % on Intel Atom with my sample.
>>>>> Testing with other CPUs and samples heavily welcome, I suspect a
>>>>> slowdown may be possible, beside it being a bit ugly.
>>>> what happens with these coeffs afterwards?
>>>> is it
>>>> s->dsp.int32_to_float_fmul_scalar(s->transform_coeffs[ch], s->fixed_coeffs[ch], gain, 256);
>>>> ?
>>>> if so maybe that could be changed to not touch the supposed to be zero
>>>> coeffs?
>>> I had that idea as well, but I have to admit I do not know, nor if
>>> I will have the time to understand the code well enough to know :-)
>> Yes the only time they're used is when they're converted to float.
> What about doing the float conversion on the fly instead of as a
> separate pass?

The only place to do it on-the-fly would be when decoding the mantissas,
which would be the natural place to do that anyway.  Then the coupling
coordinates would also need to be floating-point, as well as the stereo
rematrixing calculations.  Then the headroom and dynamic range scaling
would still need to be applied, which is now done during int-to-float
conversion.  So I doubt the change would be any faster, but it might be
worth a try.


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