[Development] Changing qreal to a float
thiago.macieira at intel.com
Wed Feb 15 09:26:31 CET 2012
On quarta-feira, 15 de fevereiro de 2012 07.38.44, gunnar.sletta at nokia.com
> Our initial idea was to change "qreal" to "double" to avoid any potential
> regression but the impact on size combined with the fact that the added
> precision is almost never needed changed our minds
There is one reason for choosing double though: it can store any 32-bit
integer without loss of precision. So doubles can be used to pass around pixel
coordinates that are 32-bit integers. That's the reason Wayland chose to use
it for all coordinates.
Float has 24 bits of mantissa precision, which is enough for 16777216x16777216
pixels. Probably good enough I'd say.
I think the most important thing is to unify the definition. Every time I met
someone from Canonical, they asked me about it because trying to build Qt-
based software on ARM revealed lots of float-double mistakes.
Note: changing qreal to float is source-incompatible and requires manual fixups
where it breaks. But it's not silent.
Thiago Macieira - thiago.macieira (AT) intel.com
Software Architect - Intel Open Source Technology Center
Intel Sweden AB - Registration Number: 556189-6027
Knarrarnäsgatan 15, 164 40 Kista, Stockholm, Sweden
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