[Interest] armv7a-hard-float in Qt android apps

Ola Røer Thorsen ola at silentwings.no
Fri Apr 29 13:55:05 CEST 2016

2016-04-29 10:11 GMT+02:00 Nuno Santos <nunosantos at imaginando.pt>:

> Code compiled and ruined fine but couldn’t notice a faster performance (I
> have profiling timers in critical parts of the application).
> Has anyone done this before?
As far as I know Qt is built with qreal as double as a default setting.

In case your cpu only does single precision floats in hardware:

Maybe try to build Qt with qreal as single precision floats?
I think the Qt configure option is "-qreal float", please check to be sure.

Makes a notable difference on my ancient arm omap3 processor, at least.

Also I'd recommend using the gcc warnings
and make sure you are just using single precision floats as much as
possible. Lots of performance is lost if you keep mixing single- and double

float a = 1.0f;
float b = 2.0*a; // BAD!
float b = 2.0f*a; // Good!

Make sure you are using single-precision math functions (use std::sin,
std::abs, not cmath sin, abs, etc). The warnings above will show you all
these cases.

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