RE: [sv-bc] static casting vs bit-stream casting

In your example the cast is illegal because the bit-stream types, two different classes in this case, have different numbers of bits.

IMHO, making classes a bit-stream type was well-intentioned, but turned out to be a very bad idea. It will not work in most verification methodologies because base classes have members that users would not want to be streamed.


Dave
Mentor Graphics

From: Daniel Mlynek [mailto:danielm@aldec.com.pl]
Sent: Thursday, September 19, 2013 9:12 AM
To: Rich, Dave
Cc: sv-bc@eda.org
Subject: Re: [sv-bc] static casting vs bit-stream casting

OK i understand rules are defined in many places in LRM.
I still think that my 1st point should be done in LRM to have some clearence change :


Type casting can also be applied to unpacked arrays and structs.
to


Type casting can also be applied to unpacked arrays classes and structs.

Classes + static cast are not well understand - I'm seeing real codes where users try to use class static cast in place where dynamic cast should be done.

LRM on one side says that class can be bitsream type while on the other says that : "Class handles and chandles are type incompatible with all other types."
So from reading the above quoation and chapter with bit stream eplanation is below legal or not

module top;
  int i;
  class C; int j; endclass
  C c;
  class D; shortint k,l; endclass
  D d;
  intial begin
    c = C'(i);   //(1)?
    i = int'(c); //(2)?
    d = D'(c);   //(3)? to be 100% LRM compatybile only this one is legal?
  end
endmodule




DANiel
W dniu 9/18/2013 5:02 PM, Rich, Dave pisze:

Actually, bit-stream casting is a static cast, and static casting only works when there are rules explaining how assignments are made between the types. If there are no explicit rules, the cast is illegal. See 6.22.4 Cast compatible





Dave

Mentor Graphics





-----Original Message-----

From: owner-sv-bc@eda.org<mailto:owner-sv-bc@eda.org> [mailto:owner-sv-bc@eda.org] On Behalf Of Daniel Mlynek

Sent: Wednesday, September 18, 2013 12:56 AM

To: sv-bc@eda.org<mailto:sv-bc@eda.org>

Subject: [sv-bc] static casting vs bit-stream casting



Those 2 features : static casting and  bit-stream casting share same syntax. It depends on the type/expression used before apostrophe which one is used.

IMHO current description need some clearence:



1. Chapter "Bit-stream casting" says "Type casting can also be applied to unpacked arrays and structs." While after reading whole chapter I suppose that at least classes need to be added to this sentence.

It would be also nice to repeat in this chapter that bit stream casting occur if the type of cast and casted variaable are not assignment compatybile



2. Static cast chapter says:

"If the expression is not assignment compatible with the casting type, then if the casting typeis an enumerated type, the behavior shall be as described as in 6.19.4, and if the casting type is a bit-stream type, the behavior shall be as described in 6.24.3."

But do not explain what to do if the expression is not assignment compatible with the casting type and is not enum nor bit-stream type.





DANiel



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