excuse me,thesr is another puzzling question about is_x
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pc : std_logic_vector(31 downto 0);
...
if not is_x(pc) then
...
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The "is_x" means that each bit of the vector are "x" or some of the vector are "x" .
I try to find the definition of "is_x". but fail.
are the "is_x" a user-defined function or constant ?