[opus] [Opus][RFC][FFT][Fixed-Point][NEON] NEON-Optimize Fixed-Point FFT?

[Phil Wang]

Hi Peter,

We are focused on CPU with NEON, and Cortex-M series do not have one.

Thanks,
Phil Wang

> -----Original Message-----
> From: Peter Robinson [mailto:pbrobinson at gmail.com]
> Sent: Thursday, December 25, 2014 6:35 PM
> To: Phil Wang
> Cc: opus at xiph.org; Zhongwei Yao; Yang Zhang; Zhou (Joe) Yu; Steve Bannister
> Subject: Re: [opus] [Opus][RFC][FFT][Fixed-Point][NEON] NEON-Optimize
> Fixed-Point FFT?
> 
> > I am working on DSP module of Ne10. I see there are fixed-point and
> > floating-point FFT inside Opus. Is fixed-point FFT only a fall back
> > for CPU without VFP? On ARMv7-A and ARMv8-A, benchmark result shows
> > that fixed-point
> > (int32) and floating-point (float32) FFT have similar performance. I
> > guess fixed-point version is not often used on these platforms. Is it
> > worth the effort to NEON-optimize fixed-point FFT?
> 
> Floating point units are optional on the ARM Cortex-M series so I believe it
> might still be worth while. The Cortex-M3-7 are based on the ARMv7
> architecture.
> 
> [1] https://en.wikipedia.org/wiki/ARM_Cortex-M#Instruction_sets