Re: [geometry] DOMRect: use of unrestricted doubles

On Sat, Oct 15, 2016 at 2:47 PM, Simon Fraser <smfr@me.com> wrote:

> https://drafts.fxtf.org/geometry/#DOMRect
>
> Using unrestricted doubles forces implementors to handle NaN and Inf
> values for x, y, width and height, and to correctly propagate NaN and Inf
> through steps used to calculate left, top, right, bottom (assuming IEEE
> rules, though the spec does not make this explicit). This is non-trivial,
> since std::min<> and  std::max<> do not follow the same NaN propagation
> rules as Math.min()/Math.max(). Implementors have to add isnan() checks to
> left, top, right, bottom implementations. Is the complexity worth it?
>

yes. We allowed this so NaN and Inf would signal when matrix calculations
hit edge conditions.
Instead of throwing or giving inaccurate result, it was decided to allow
the values so authors can check for those. The alternative would be to
throw and we feared that this would break a lot of code since people don't
test with exceptions.

See also the thread here:
https://lists.mozilla.org/pipermail/dev-platform/2014-June/005091.html

When I did the implementation in Firefox, this actually made the code
easier to implement since I didn't have to add a bunch of conditionals and
could just rely on the FPU to do the correct thing.