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

>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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