Re: [proximity] Meaning of negative values

On 13 May 2014, at 17:11, Hirsch Frederick (Nokia-CTO/Boston) <frederick.hirsch@nokia.com> wrote:

> My understanding is that meaningful values are positive in the range of min - max but that a �negative infinity� value is used to represent �undefined�.
> 
> Value is a double so it can be negative, but only positive values have meaning for this API. The negative infinity value is used as a special case indicator to mean no value has been assigned (e.g. not supported or available).

Correct.

> Thus for min, max and value the negative and positive infinity values are used to indicate �no defined value� - I guess Javascript NaN or �undefined� could be used instead of this convention, but this way it is always a number and just requires a value test.

This allows to differentiate between the "value is zero" and "value is not known�, and is easier to use with comparison operators than NaN or undefined as Frederick notes.

> I wonder if there is a documented set of conventions for the HTML5 family of specs that would include this.

The HTML spec does use this convention to set certain "not known� values as negative or positive Infinity. The spec itself serves as a documented set of conventions, and there�s no separate maintained document for that, AFAIK.

> The language about returning the �value it was initialized to� is not very clear. What it really means is �return the value determined by the device which is either the actual value or the indicator that no value is available�.

The �value it was initialised to� is established language for initialising attributes of an event, used by specification that make use of events.

> Thus in general no negative values should be found other than negative infinity.

Correct.

> Does this make sense?

Thanks,

-Anssi

Received on Wednesday, 14 May 2014 07:07:51 UTC