[opus] fixed point version for celt_pitch_xcorr on aarch64

[Zhongwei Yao]

>-----Original Message-----
>From: Timothy B. Terriberry [mailto:tterribe at xiph.org]
>Sent: Friday, January 30, 2015 4:42 PM
>To: Zhongwei Yao; opus at xiph.org
>Cc: Phil Wang
>Subject: Re: [opus] fixed point version for celt_pitch_xcorr on aarch64
>
>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.
Intrinsics performance on recent toolchain (e.g. gcc 4.9) is comparable to hand-written assembly. WebRTC's audio processing module has been switch to intrinsics on ARM platform. Here are some cases:
https://webrtc-codereview.appspot.com/23349004/
https://webrtc-codereview.appspot.com/36689004/
https://webrtc-codereview.appspot.com/32749004/

Thanks,
Zhongwei

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