Re: [sv-ec] RE: [sv-bc] Issue 41 - real in associative array

From: Neil Korpusik <Neil.Korpusik_at_.....>
Date: Mon Apr 27 2009 - 15:30:29 PDT
I suggest that both the sv-ec and the sv-bc vote on the proposal.

Neil




On 04/27/09 13:44, Stuart Sutherland wrote:
> I'm not sure which committee now owns Mantis 2861 (ballot comment 41), but I
> have uploaded a proposal to correct the example in 7.9.5, per the request of
> the balloter and per Arturo's comment, below.  I have also searched Clause 7
> to make sure the example was not referenced elsewhere in the clause, and it
> is not.
> 
> Mantis 2681 should be ready for an e-mail vote.
> 
> Stu
> ~~~~~~~~~~~~~~
> Stuart Sutherland
> stuart@sutherland-hdl.com
> (503) 692-0898
> 
> 
>> -----Original Message-----
>> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of Arturo
>> Salz
>> Sent: Friday, April 24, 2009 11:04 AM
>> To: Gordon Vreugdenhil; jonathan.bromley@doulos.com
>> Cc: SV_BC List; sv-ec@eda.org
>> Subject: [sv-ec] RE: [sv-bc] Issue 41 - real in associative array
>>
>> You should include SV-EC in this discussion.
>>
>> For the record, I am in complete agreement with Jonathan. The actual
> ballot
>> issue is trivially resolved by changing the  example, which is evidently
>> incorrect as it contradicts LRM verbiage that explicitly disallows real
> types
>> as indices of associative arrays. That has always been the LRM intent and
> I
>> see no reason to change it since IMHO it adds no value to users and does
>> create the potential for surprises and confusion. At this point I would
>> consider adding indices of type real to associative arrays as an
> enhancement
>> that lies outside the ballot issue.
>>
>>         Arturo
>>
>> -----Original Message-----
>> From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of Gordon
>> Vreugdenhil
>> Sent: Friday, April 24, 2009 10:44 AM
>> To: jonathan.bromley@doulos.com
>> Cc: owner-sv-bc@eda.org; SV_BC List
>> Subject: Re: [sv-bc] Issue 41 - real in associative array
>>
>>
>> Jonathan, I completely agree with your point but
>> not necessarily the conclusion.  Anyone desiring
>> to do what you are doing below would recode the
>> example using something valid (a list of reals
>> for example) and then use "==" and get into the
>> same fundamental problem.  Alternatively, they
>> might just do $realtobits and use an associative
>> array on the bit vectors (with the same issue again).
>>
>> Users can hurt themselves with reals --
>> if they care, I'd expect a user to create a
>> "tolerance function" to normalize reals into
>> representative values within some tolerance range
>> and operate on those values.  I don't see much
>> point in arbitrarily restricting associative
>> arrays of real in order to try to protect the user.
>>
>> Gord.
>>
>>
>> jonathan.bromley@doulos.com wrote:
>>>> I took a closer look at issue 41.  The LRM certainly does
>>>> intentionally restrict the existence of "real" in any
>>>> component of an associative array index type.  This is a
>>>> bit odd since the general statement is simply that equality
>>>> (and some internal ordering relation) is defined and certainly
>>>> equality is defined for real.  Personally I think that it makes
>>>> more sense to drop the restriction than to modify the example
>>>> but if there is any concern about dropping the restriction,
>>>> then we should modify the example to be consistent with the
>>>> normative text.
>>> Gord is clearly right to say that equality is defined for
>>> reals, in the sense that there is an equality comparison
>>> operator and it does something vaguely useful.  However,
>>> I am (as a matter of principle) uncomfortable about
>>> any attempt to use reals to model or represent discrete
>>> values; indeed, I would always regard testing reals for
>>> equality as being fragile and untrustworthy.  You just
>>> KNOW that someone will complain when this doesn't do
>>> what they expect:
>>>
>>>   real thirty_degrees = $atan(1.0) * 2.0 / 3.0;
>>>   bit visited[real];
>>>   visited[thirty_degrees] = 1;
>>>   assert (visited[$asin(0.5)]);
>>>
>>> So I would prefer to see the ballot feedback implemented
>>> as-is by modifying the example to avoid the use of real.
>> --
>> --------------------------------------------------------------------
>> Gordon Vreugdenhil                                503-685-0808
>> Model Technology (Mentor Graphics)                gordonv@model.com
>>
>>
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> 
> 

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Received on Mon Apr 27 15:31:20 2009

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