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

Darin Adler darin at apple.com
Thu Oct 11 09:17:42 PDT 2012

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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