[opus] ARM NEON optimization -- celt_fir()

[Jonathan Lennox]

Hi, Linfeng —

Please note the aarch64 optimization patches I submitted in November and December (which Tim still hasn’t gotten around to reviewing).  As they used Neon intrinsics, several of these actually applied to both armv7 and aarch64 Neon.

In particular, note http://lists.xiph.org/pipermail/opus/2015-December/003339.html , which added a Neon-optimized version of xcorr_kernel.  xcorr_kernel is used in celt_fir, celt_iir, and celt_pitch_xcorr.

> On Jun 17, 2016, at 5:09 PM, Linfeng Zhang <linfengz at google.com> wrote:
> 
> Hi all,
> 
> This is Linfeng Zhang from Google. I'll work on ARM NEON optimization in the
> next few months.
> 
> I'm submitting 2 patches in the following couple of emails, which have the new
> created celt_fir_neon().
> 
> I revised celt_fir_c() to not pass in argument "mem" in Patch 1. If there are
> concerns to this change, please let me know.
> 
> Many thanks to your comments.
> 
> Linfeng Zhang
> 
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