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

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