heads up - Qt qreal difference on ARM

[Florian Weimer]

On 08/02/2013 09:45 AM, Richard W.M. Jones wrote:

> https://developer.android.com/training/articles/perf-tips.html#avoidfloat
>
> there's no difference on modern hardware.  (Note I didn't verify this.)

That's about the Dalvik implementation.  Other comments on that page 
suggest that it's so inefficient that a difference between float and 
double argument passing and computation overhead might be lost in that 
noise.

Hardware floating point operations except division should only take one 
cycle, for both single and double precision.  If VFP requires passing 
double values in 32-bit register pairs, that might add some overhead, 
though.

> Judging by a google search for "qreal" "float" "arm" this difference
> causes endless problems.  I even found a Fedora build bug related to it.
>
> However it's a matter for upstream to fix it.  Not something we could
> carry around only in Fedora IMHO.

I would expect that consistency across Fedora architectures is more 
important than alignment to upstream.

-- 
Florian Weimer / Red Hat Product Security Team