subtype question

[John Smith]

Hi,

What is name of the following language construct "rtype'(others => 'X')" and
what does here?

function EXT(ARG: STD_LOGIC_VECTOR; SIZE: INTEGER)
return STD_LOGIC_VECTOR is
constant msb: INTEGER := min(ARG'length, SIZE) - 1;
subtype rtype is STD_LOGIC_VECTOR (SIZE-1 downto 0);
variable new_bounds: STD_LOGIC_VECTOR (ARG'length-1 downto 0);
variable result: rtype;
-- synopsys built_in SYN_ZERO_EXTEND
begin
-- synopsys synthesis_off
new_bounds := MAKE_BINARY(ARG);
if (new_bounds(0) = 'X') then
result := rtype'(others => 'X');
return result;
end if;
result := rtype'(others => '0');
result(msb downto 0) := new_bounds(msb downto 0);
return result;
-- synopsys synthesis_on
end;


Thanks

 

[Jim Lewis]

John,
(others => 'X') is an aggregate
rtype' is a type qualifier used to coerce the input to be of a particular.

I don't see any reason why the type qualifier was required in the
piece of code you referenced below. The assignment to the variable
should have taken care of this.

Cheers,
Jim