RE: [sv-ec] mantis 2183 (solve-before constraints)

Ray,

I believe your derivation is incorrect. How is (x+y) equivalent to t1 ==
x+y ?

I think the problem is the use of expression in expression_list. This
mantis is intended to allow finer granularity in designating the
distribution ordering, but not the introduction of new constraints.
Frankly, I don't know what (x+y) could possibly mean as a constraint -
it is certainly invalid constraint syntax. Perhaps we need a different
syntactical construct that designates part-selects and item-selects,
which seems to cover the set you had in mind.

Also, the solve..before construct can only affect the distribution. It
should not partition the constraint set, which you seem to imply that it
does. Did I misunderstand that?

	Arturo

-----Original Message-----
From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
Ryan, Ray
Sent: Monday, March 24, 2008 3:08 PM
To: sv-ec@eda.org
Subject: [sv-ec] mantis 2183 (solve-before constraints)


In considering the champions feedback and the SV-EC discussion, I tried
to find a better way to state restriction on expressions in a
solve-before constraints (that still allowed)
- names of random 'variables' 
- rand fields of random variables 
- bit selects of random varialbes 
- references to elements of a random array 
- field of an element of ...
- ...

My conclusion is that special restrictions for expesssion in a
solve-before constraint (beyond those for constraints in general) are
not required.

For the case where an solve-before expression is not a "simple random
variable or field of a random variable). IE
    rand int x,y,z;
    ...
    constraint C {
        solve (x+y) before z;
    }
This should have the same semantics as
    rand int x,y,z;
    rand int t1;
    constraint C {
        t1 == x+y;
        solve t1 before x;
    }

Since the latter can be coded with the current LRM, allowing expressions
in a solve-before constraint doesn't add any new solver capabilities -
rather it is a simplification.


I have added a modified proposal (errata_2183d.htm) that allows
expression in solve-before constaints and removes the prior resrictions.


Regards,
Ray Ryan


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