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

Justin Ruggles justin.ruggles
Thu Jan 14 02:54:37 CET 2010

Michael Niedermayer wrote:

> On Wed, Jan 13, 2010 at 06:32:27PM -0500, Justin Ruggles wrote:
>> 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.  If
>> we don't zero the integer coeffs, we will need to zero the float coeffs
>> because the IMDCT uses all 256.
> are the float coeffs ever written to besides in int32_to_float_fmul_scalar ?
> because if not you could keep track of the last non zero coeff and just
> zero upto that each time

The bandwidth can change from block to block, so there could be leftover
 higher frequency coeffs from the last block.


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