RE: [sv-bc] confusion in determining the type of an self determined binary expression during evalution of type operator

 

 

-----Original Message-----
From: owner-sv-bc@server.eda.org [mailto:owner-sv-bc@server.eda.org] On
Behalf Of Steven Sharp
Sent: Wednesday, October 24, 2007 9:31 PM
To: sharp@cadence.com; Greg.Jaxon@synopsys.com; Feldman, Yulik
Cc: sv-bc@server.eda-stds.org; gordonv@model.com
Subject: RE: [sv-bc] confusion in determining the type of an self
determined binary expression during evalution of type operator

 

Your rule includes matching the type of the context for integral types.

So the next thing you would have to do is define what the type of the

context is.  The existing LRM only defines the size and signedness of

the context.

[Yulik] You're right. Defining the type of the context should be a part
of the definition of types of expressions.

 

After that, there will be other issues that require more special

exceptions to your rules.  For example, your rules produce the wrong

result for 2-state types.  If you have

 

      int i, j;

      

      type(cond ? i : j)

 

your rules would say that the type is int.  But the result is definitely

a 4-state vector, so it cannot be type int.

[Yulik] Unfortunately, you're right. This weird x-value behavior of
conditional operators is more confusing than helping, in my eyes. It
looks like the problem started with the introduction of 2-state types,
which were introduced, but the semantics of conditional operators was
not updated accordingly. I think it would be more appropriate if the
type of the conditional would be calculated by the above simple rules,
and any possible x-values would be converted to 0s, if the corresponding
bit of the result is a part of 2-state type. If someone needs
x-propagation, he should use 4-state types for all relevant expressions,
to ensure that the type of the conditional is 4-state and the x's are
propagated.

 

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