[opus] fixed point version for celt_pitch_xcorr on aarch64

[Jean-Marc Valin]

Speaking of conversion, do we actually have Neon code for int<->float
conversion?

	Jean-Marc

On 01/02/15 05:26 PM, Timothy B. Terriberry wrote:
> Viswanath Puttagunta wrote:
>> Could you please elaborate on "It would be nice to have"? Specifically:
>> - Are there use cases where fixed point is preferred when AAarch64 has
>> mandatory support for floating point both in regular CPU as well as
>> NEON?
> 
> Even on x86, when the complexity setting is below the maximum, then for 
> medium-low bitrate speech the fixed-point encoder will generally be 
> faster, because much of the SILK processing uses exact integer math, and 
> this avoids several float->int->float round trips. That's why the x86 
> intrinsics code Cisco contributed focused on fixed-point, for example.
> 
> I have not tested on aarch64, but I expect similar properties to hold.
> 
> It also depends on the rest of your pipeline. If your whole audio 
> pipeline is fixed-point (which is common in real-time stacks), then 
> you'd have to pay additional conversion penalties to use the 
> floating-point API.
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