[webkit-dev] Transformations precision: double -> float

Gabor Rapcsanyi rgabor at inf.u-szeged.hu
Fri Oct 12 02:08:24 PDT 2012

Yes I agree that we need to do some measures to see the benefits of floats.
But it's not just about the performance and memory gain of the floats, I 
would like to make ARM SIMD optimizations for the transformation 
functions to fasten up them, but ARM NEON technology only works with 
floats that's why I want to change the doubles.
I would prefer a typedef solution to make this configurable as Ryosuke 
said, and then the ports could chose whether they need floats, doubles 
or long doubles.

- Gabor
> On Oct 10, 2012, at 9:00 AM, Gabor Rapcsanyi <rgabor at inf.u-szeged.hu> wrote:
>> That was a long time ago and there were no objections
>>> Unless there's something in the spec requiring double precision it makes sense to move away from double precision throughout WebKit.
> I’m a little concerned about this.
> The programming interface to the graphics system on OS X uses doubles, so it’s likely we’ll be introducing float to double conversions for at least that platform if we change things inside WebKit that are currently doubles to float en masse.
> Similarly, the native data type for numbers in JavaScript is double. So any time we are passing a number from JavaScript to WebKit it’s likely that additional double to float conversions will be required as we change internals to use doubles instead of floats.
> On the other hand, there may also be performance boost or memory gains from using float instead of double.
> If we do make this change, I think we need to do performance testing as we do so, perhaps on more than one platform, to see if these changes are leading to benefits or not.
> I also think that “we should always use float unless a spec mandates double” is probably not the right rule of thumb. There are many factors other than “a spec” at play here.
> -- Darin

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