RE: [sv-ac] Re: [sv-bc] Re: if-else

>From: "Rich, Dave" <Dave_Rich@mentor.com>

>Has anyone come up with a case where 1'b0 would not work? What about '0?

You mean for the "equivalent" comparison?  Sure:

module top;
initial
begin
  if (1'sb1>>>1)
        $display("expression true");
  if ((1'sb1>>>1) != 1'b0)
        $display("(expression != 1'b0) true");
  if ((1'sb1>>>1) != '0)
        $display("(expression != '0) true");
  if ((1'sb1>>>1) != 1'sb0)
        $display("(expression != 1'sb0) true");
end
endmodule

In a correct implementation, this prints

expression true
(expression != 1'sb0) true

and none of the others.  Using an unsigned zero gives incorrect results.

Steven Sharp
sharp@cadence.com


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