Array rotate : "Range bound must be a constant" in synthesis

Hello

I have one error message "Range bound must be a constant" duriung
synthesis.

I intend to rotate a variable sized integer array.
Array looks like {size, element,..,element }.
Number of elements = size.
I wish to get new array, rotated by "pos" value.

For example,
old array = { 4, 2, 3, 1, 4} and pos = 2
new array = { 4, 3, 1, 4, 2}.

Another example,
old array = { 5, 4, 2, 1, 3, 5 } and pos = 3
new array = { 5, 1, 3, 5, 4, 2 }

In order to implement that, I used "function", as shown in the
following.

1. I considered record type "parameters"

---- parameter to pass
type para is array (0 to size) of integer range 0 to size;
type parameters is record
old : para; -- old array
pos : integer range 0 to size; -- pos
end record;

2. I wrote a function below.

The code is not synthesizable.
Does anyone have idea how to make this synthesizable?
Thankyou.


-- generate new array from old array
function NEW_ARRAY( Temp: parameters ) return para is
variable array_out : para; -- new array
variable CTRL : integer range 0 to size; -- pos
variable IDX : integer range 0 to size; -- size
begin

CTRL := Temp.pos ;
IDX := Temp.old(0);

array_out(0) := Temp.old(0);

if ( IDX = 0 or CTRL = 0 ) then array_out := (others => 0 );
else

for I in CTRL to IDX loop
array_out(I - CTRL + 1) := Temp.old(I); ---- problematic
end loop;

for I in 1 to CTRL-1 loop
array_out(I + IDX - CTRL + 1) := Temp.old(I); ---- problematic
end loop;

end if;
return array_out;
end NEW_ARRAY;

Pasacco