Re: [sv-bc] query regarding casting

I don't think unpacked unions are bit-stream types either.

 

But that example has been there a long time --

 

           http://www.eda-stds.org/sv/3.0_LRM.pdf

 

-- Brad

 

________________________________

From: Subhamoy Pal [mailto:subhamoy@cal.interrasystems.com] 
Sent: Wednesday, June 28, 2006 10:55 PM
To: Brad Pierce
Cc: sv-bc@eda-stds.org
Subject: Re: [sv-bc] query regarding casting

 

Brad,
then does it mean we can not cast an unpacked aggregate, containing
real/shortreal, to a bitstream type? If so, then the LRM example in
4.14,
 
tagbits t = tagbits'(a[3]); // convert structure to array of bits

is not correct because 'a[3]' can contain real type as a part of it.

-- Subhamoy


Brad Pierce wrote:



Subhamoy,

 

I think the only way to bit-stream reals or shortreals is with the
$realtobits(), $bitstoreal(), $shortrealtobits() and $bitstoshortreal()
system functions.  Reals and shortreals are not bit-stream types.

 

-- Brad

 

________________________________

From: owner-sv-bc@eda-stds.org [mailto:owner-sv-bc@eda-stds.org] On
Behalf Of Subhamoy Pal
Sent: Wednesday, June 28, 2006 5:32 AM
To: sv-bc@eda-stds.org
Subject: [sv-bc] query regarding casting

 

In SV LRM 4.14, I found the following example:

typedef struct {
bit isfloat;
union { int i; shortreal f; } n; // anonymous type
} tagged_st; // named structure

typedef bit [$bits(tagged_st) - 1 : 0] tagbits; // tagged_st defined
above

tagged_st a [7:0]; // unpacked array of structures

tagbits t = tagbits'(a[3]); // convert structure to array of bits

Here a[3] can be assigned with '{isfloat:1, n:'{f:2.5}}. Here the
problem is if we consider the 33 bits needed to represent value of a[3],
the least significant 32 bits will be a representation for
shortreal(i.e. the memory representation will be of C float type).
Treating this 32 bit representation as bitstream representation does not
mean anything significant.
In LRM, though I found how a real or shortreal data type can be casted
to a bit stream, but I can not find any LRM verse which specifies how to
cast an unpacked aggregate, containing real/shortreal data, to a packed
aggregate. Can anyone please specify any such LRM section and verse?

--Subhamoy