Re: [sv-ec] Completing my coverage thought...

Swapnajit,

The discussion we were having was a continuation of the SV-EC
conference call which is why you misunderstood this.

By "empty bins" here we did not mean "bins that were never
covered" but rather "bins with no elements in their value set".
This arises due to the interaction of ignore_bins and/or having
more bins than values.

The LRM has not defined whether bins that have no elements in
their value set are supposed to be included in the computation.
Arturo and I are in agreement that they should not.  As I noted
in my follow-up email, there is still edge case behavior to
discuss - the situation in which there are no bins with values
in their value sets.

Gord.



Swapnajit Chakraborti wrote:

> Hi Arturo & Gord,
> 
> As per LRM, coverage for a coverpoint (section 18.10.1)
> is defined as:
>   num_covered_bins/num_all_defined_bins
> 
> Again, num_covered_bins is actually the number of bins for which
> at_least count is reached (count >= at_least). 
> 
> Now, in your discussion you have mentioned "num_non_empty_bins".
> I am assuming the following definition of "num_non_empty_bins".
> 
> num_non_empty_bins = num_covered_bins ( count >= at_least) + 
>                      (number of bins which have 0 < count < at_least) 
> 
> Is the above definition correct?
> 
> In that case, if we define coverage as follows (as you mentioned):
> 
>>>      num_covered_bins / num_non_empty_bins
> 
> 
> We are completely removing the number of empty bins from
> the denominator. 
> 
> Shouldn't the denominator be the total number of bins defined for 
> a coverpoint which is:
> num_all_defined_bins = num_non_empty_bins + num_empty_bins
> 
> Note that num_all_defined_bins will not include ignore/illegal bins.
> 
> Thx,
> Swapnajit.
> 
> Gordon Vreugdenhil wrote:
> 
>>Arturo Salz wrote:
>>
>>>Gord,
>>>
>>>I agree that it's best to not consider empty bins and compute coverage
>>>as:
>>>      num_covered_bins / num_non_empty_bins
>>>While both mechanisms described by you allow coverage to be 100%, this
>>>one also exhibits the nice property of being 0 when nothing is run. I
>>>believe
>>>it is counterintuitive to have non-zero coverage when no bins are
>>>covered.
>>>
>>>      Arturo
>>
>>Arturo,
>>
>>That's fine with me.  An edge case -- 18.10.1 doesn't define any rules for
>>results when the number of non-empty bins is 0.  So, should this be
>>defined to be:
>>   1) illegal
>>   2) 100% coverage
>>   3) 0% coverage
>>
>>I don't think I would want (1) to be an LRM requirement (an implementation
>>might warn of course), but for parameterized ignore_bins, etc. the situation
>>might actually be reasonable.
>>
>>If the user anticipates the scenario, I think that (2) is the best
>>choice since otherwise full coverage can't be reached.
>>
>>Gord.
>>
>>
>>>
>>>-----Original Message-----
>>>From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
>>>Gordon Vreugdenhil
>>>Sent: Monday, January 09, 2006 12:52 PM
>>>To: SV_EC List
>>>Subject: [sv-ec] Completing my coverage thought...
>>>
>>>Just to complete my thought regarding coverage before the
>>>call was dropped -- my basic question is whether the coverage
>>>percentage is:
>>>     num_covered_bins / num_non_empty_bins
>>>or:
>>>     (num_covered_bins + num_empty_bins) / (num_non_empty_bins +
>>>num_empty_bins)
>>>
>>>(i.e. is an empty bin not considered at all or is it
>>>trivially covered?)
>>>
>>>I think that the former is perferable, but I don't know for sure.
>>>
>>>Gord.
>>
>>--
>>--------------------------------------------------------------------
>>Gordon Vreugdenhil                                503-685-0808
>>Model Technology (Mentor Graphics)                gordonv@model.com

-- 
--------------------------------------------------------------------
Gordon Vreugdenhil                                503-685-0808
Model Technology (Mentor Graphics)                gordonv@model.com