[opus] fixed point version for celt_pitch_xcorr on aarch64

[Viswanath Puttagunta]

On 30 January 2015 at 02:41, Timothy B. Terriberry <tterribe at xiph.org> wrote:
> Zhongwei Yao wrote:
>> Hi, all,
>>
>> Does Opus need celt_pitch_xcorr’ s fixed point version for ARM aarch64
>> architecture? If yes, which version does Opus prefer: assembly or
>> instrinsics?
>
> It would be nice to have one. I don't have a lot of experience with
> aarch64 (I still haven't been able to obtain a dev board), so I don't
> really know how intrinsics compare to assembly. Historically, intrinsics
> performance on most platforms has been significantly below that of
> hand-written assembly, and the tool support is more of a headache, which
> is why we've favored hand-written assembly, but getting some kind of
> vectorization is better than the serial code we currently have.

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?

- Does using Fixed Point on any CPU (regardless of ARMv7/ARMv8 or
otherwise) have notable advantages over using floating point?
(performance, compatibility or otherwise)

- If yes to above question, does same logic apply to ARMv8?


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