RE: [sv-bc] part selects on arbitrary expressions

 

> I would suggest to normalize the range to the (0,N-1) bounds, but to

> decide on either [0:N-1] or [N-1:0] choice based on the kind of type

> declaration from which the part select selects a part. If the MSB of
the

> type declaration is bigger than LSB, then use [N-1:0] type for the
part

> select; otherwise, use the [0:N-1] type. This way the order of
"element

> significance" will be preserved.

 

Normalize, but conserve endianness - that is a new proposal!

Looking at only classical part selects, it is even pretty reasonable.

Could you write out the result type for A[X+:L] and A[X-:L], please?

Do you want it to take endianness from the +/- syntax, or from A?

[Yulik] From A. The +/- is just a syntactical convention. It should not
affect the type - in the same way that it doesn't affect the choice of
whether X is going to be the LSB or MSB of the selection - this choice
depends only on the type of A.

 

Fortunately we're disputing a pretty minor point in the LRM.  How often

are the results of part selects re-indexed anyway?

[Yulik] Not often, but still we need to have definition that takes that
into account if it happens. 

 

BTW, the reason I'm suggesting this "endianness conservation" is because
today it is enough to compare the types of the expressions being
assigned to decide on what bit should go where. If the endianness will
not be preserved in the types of the part selects, there will be a need
to also to look on the expressions themselves and check whether they are
part selects and what is the endianness of the types of the objects they
select. By having endianness preserved, the choice is going to be
simpler and consistent with the rest of expression kinds.


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