[maemo-developers] Performance of floating point instructions

[From: Laurent Desnogues]

On Wed, Mar 10, 2010 at 10:46 AM, Ove Kaaven <ovek at arcticnet.no> wrote:
> Alberto Mardegan skrev:
>> Does anyone know any tricks to optimize certain operations on arrays of
>> data?
>
> The answer to that is, obviously, to use the Cortex-A-series SIMD
> engine, NEON.
>
> Supposedly you may be able to make gcc generate NEON instructions with
> -mfpu=neon -ffast-math -ftree-vectorize (and perhaps -mfloat-abi=softfp,
> but that's the default in the Fremantle SDK anyway), but it's still not
> very good at it, so writing the asm by hand is still better... and I'm
> not sure if it can automatically vectorize library calls like sqrt.

One has to be careful with that approach:  Cortex-A9 SoC won't
necessarily come with a NEON SIMD unit, as it's optional.  So it'd
be better to also include code that doesn't assume one has a
NEON unit.


Laurent