Re: [sv-bc] query regarding $bits function

>From: Surya Pratik Saha <spsaha@cal.interrasystems.com>

>LRM mentions:
>*It shall be an error to enclose a function that returns a dynamically 
>sized data type.
>
>*Actually from this text the confusion comes. How a function can return 
>"dynamically sized data types". Can you give an e.g.?

Yes, that would be the text that applies to your testcase.  The wording
is rather poor.  It should not say "enclose a function that returns a
dynamically sized data type", but something more like "enclose a function
call that returns a value of a dynamically sized data type".

Notice the previous sentence about how the result of $bits is determined
without evaluating the expression.  This is the issue that I raised with
the testcase, though I didn't know whether the LRM addressed it.

Your testcase is an example of this, and is therefore illegal.



>-------- Original Message  --------
>Subject: Re:[sv-bc] query regarding $bits function
>From: Steven Sharp <sharp@cadence.com>
>To: sv-bc@eda-stds.org, sarani@cal.interrasystems.com
>Date: Tuesday, February 05, 2008 11:50:06 PM
>>> From: Sarani Roy <sarani@cal.interrasystems.com>
>>>     
>>
>>   
>>> According to LRM:
>>> It shall be an error to use the $bits system function directly with a
>>> dynamically sized data type identifier.
>>>     
>>
>> I don't think this LRM text is relevant to your example.  When this text
>> refers to a "dynamically sized data type identifier", it does not mean
>> "an identifier (e.g. variable) of a dynamically sized data type".  It
>> means "a data type identifier (e.g. typedef name) that represents a
>> dynamically sized type".  You cannot ask "how big is a string type?"
>> You have to ask "how big is this particular string?"
>>
>>
>>   
>>> Is this valid :
>>>
>>> module top( input  [10:0] in1, input clk);
>>> int bit_count;
>>> string str1;
>>>
>>> function string my_func(input bit [10:0] in1);
>>>    begin
>>>       str1 = string'(in1);
>>>      return str1;
>>>    end
>>> endfunction
>>>
>>> always@(clk)
>>>  bit_count = $bits(my_func(in1));
>>> endmodule
>>>
>>> Some standard simulators are passing.
>>>     
>>
>> The issue here is presumably that you can normally determine $bits
>> of an expression without having to evaluate it.  In this case, you
>> would have to evaluate it and actually call the function, possibly
>> causing side effects.  I can see how some implementors might decide
>> that this was improper.
>>
>> Steven Sharp
>> sharp@cadence.com
>>
>>
>>   
>
>
>
>
>
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Steven Sharp
sharp@cadence.com


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