Unique constant per instantiation

if its a constant, you can do whatever maths you want in the function call. So just have a generic called "SEED" or something that then does something inside the f_generate_unique_id function.

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_misc.all;
use ieee.numeric_std.all;
entity rand_test is
  generic 
  (
    SEED  : positive := 22553362
  );
  
  port
  (
    a : in  std_logic;
    b : out std_logic
  );
    
end entity rand_test;
architecture test of rand_test is
  function set_init_val return std_logic_vector is
    
    use ieee.math_real.all;  --for uniform procedure
    
    variable rand         : real;
    variable seed1, seed2 : positive := SEED;
    variable result       : integer;
      
  begin
    uniform(seed1, seed2, rand);
    result := integer(((rand - 0.5) *2.0) * real(integer'high));  --makes random range from integer'low to integer'high by making "rand" range -1 to +1
    
    return std_logic_vector( to_signed(result, 32));
  end function;
  constant C_MYID : std_logic_vector := set_init_val;
  
begin
  b <= a and and_reduce(C_MYID);
  
end test;