[maemo-developers] Performance of floating point instructions

[From: Kimmo Hämäläinen]

On Wed, 2010-03-10 at 10:46 +0100, ext Ove Kaaven 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.

You can also put the CPU to a "fast floats" mode, see hd_fpu_set_mode()
in
http://maemo.gitorious.org/fremantle-hildon-desktop/hildon-desktop/blobs/master/src/main.c

N900 has support for NEON instructions also.

-Kimmo