Re: [sv-bc] FW: Clarification on unions (from Stu Sutherland)

A regular (unpacked) union is an aggregate by the definition in section
3.13.

That means as a whole, it can only be copied or compared to equivalent
types. (and before anybody asks, the result of a comparison of two
unions can not be defined because the alignment of members in the union
is not defined)

Whether or not it can be used in $display is a different story. At the
last SV-BC meeting we discussed proposing an errata to bring all the
file I/O routines up to spec with the rest of SV.

Dave

David W. Smith wrote:

>-----Original Message-----
>From: Stuart Sutherland [mailto:stuart@sutherland-hdl.com]
>Sent: Thursday, April 01, 2004 7:58 AM
>To: David.Smith@Synopsys.COM
>Subject: Clarification on unions
>
>David,
>
>I'm not sure which subcommittee this question should go to. Could you
>please forward this question to the right group?
>
>Is it legal to access a union using just the union name without a member
>name? If so, what are the rules for what type is read from the union? For
>example, is the following legal?
>
> union {
> int unsigned u;
> int s;
> } foo;
>
> initial begin
> foo.i = -5;
> $display("foo = %d", foo); //is this reference to foo legal?
> end
>
>I could not find anything in the LRM on this, for unpacked, packed or tagged
>unions, although the following sentence might be on this topic (it is not
>clear to me). It seems to me that this should be covered in section 3.11.
>
>Stu
>~~~~~~~~~~~~~~~~~~~~~~~~~
>Stuart Sutherland
>stuart@sutherland-hdl.com
>503-692-0898
>
>
>
>

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