[maemo-developers] Performance of floating point instructions

[From: Eero Tamminen]

Hi,

ext Alberto Mardegan wrote:
> Kimmo Hämäläinen wrote:
>> 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.
> 
> This sounds interesting!
> 
> Is there any performance penalty if this switch is done often?

Why you would switch it off?

Operations on "fast floats" aren't IEEE compatible, but as far as
I've understood, they should differ only for numbers that are very close
to zero, close enough that repeating your algorithm few more times would
produce divide by zero even with IEEE semantics (i.e. if "fast float"
causes you issues, it's indicating that there's most likely some issue
in your algorithm).


	- Eero