[opus] fixed point version for celt_pitch_xcorr on aarch64

[Viswanath Puttagunta]

On 1 February 2015 at 19:53, Jean-Marc Valin <jmvalin at jmvalin.ca> wrote:
>
> Speaking of conversion, do we actually have Neon code for int<->float
> conversion?
NEON does support VCVTxx instructions, which at first glance seem to
be useful to be able to do this. I will investigate this further..
Thanks for pointing this out.

>
>         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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