[opus] 2 patches related to silk_biquad_alt() optimization

[Jean-Marc Valin]

On 24/04/17 08:03 PM, Linfeng Zhang wrote:
> Tested on my chromebook, when stride (channel) == 1, the optimization
> has no gain compared with C function.

You mean that the Neon code is the same speed as the C code for
stride==1? This is not terribly surprising for an IIRC filter.

> When stride (channel) == 2, the optimization is 1.2%-1.8% faster (1.6%
> at Complexity 8) compared with C function.

Is that gain due to Neon or simply due to computing two channels in
parallel? For example, if you make a special case in the C code to
handle both channels in the same loop, what kind of performance do you get?

> Please let me know and I can remove the optimization of stride 1 case.

Yeah, if there's Neon code that provides no improvement over C, let's
stick with C. And if you manage to write C code that has the same
performance as the Neon code, then that would also be better (both
easier to maintain and more portable).

> If it's allowed to skip the split of A_Q28 and replace by 32-bit
> multiplication (result is 64-bit), probably it could be faster on NEON.
> This may change the encoder results because of different order of
> adding, shifting and rounding.

I'm not sure what you mean for that.

	Jean-Marc

> Thanks,
> Linfeng
> 
> 
> On Wed, Apr 19, 2017 at 10:23 PM, Jean-Marc Valin <jmvalin at jmvalin.ca
> <mailto:jmvalin at jmvalin.ca>> wrote:
> 
>     Hi Linfeng,
> 
>     Thanks for the patches. I'll have a look and get back to you. What kind
>     of speedup are you getting for these functions? On what command line?
> 
>     Cheers,
> 
>             Jean-Marc
> 
>     On 19/04/17 12:29 PM, Linfeng Zhang wrote:
>     > Hi,
>     >
>     > Attached are 2 patches related to silk_biquad_alt() optimization.
>     Please
>     > review.
>     >
>     > Thanks,
>     > Linfeng Zhang
>     >
>     >
>     >
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