with Text_io; use Text_io;
procedure PRIMES is       -- Eratosthene's sieve
  package IIO is new Text_IO.Integer_io(integer); --need integer output
  N:constant integer:=1500; --largest number to be considered
  SCREEN_WIDTH:constant integer:=60;
  LINES:constant integer:=N / screen_width - 1;
 
  type PRIME_CLASS is (UNKNOWN, PRIME, COMPOSITE);
 
  type PRIME_CLASSES is array(1..N) of PRIME_CLASS;
 
  STATE: PRIME_CLASSES:=(1..N=>UNKNOWN); -- State of numbers...
  MULTIPLE:integer;
 
begin
  iio.Put(1); STATE(1):=PRIME;
 
  for P in 2..N loop  -- For each possible prime in turn...
 
    if STATE(P)=UNKNOWN then -- it isn't a multiple of a smaller prime
 
	iio.put(P); STATE(P):=PRIME;
 
	MULTIPLE:=P+P;
	for MULTIPLIER in 2..N loop -- multiple = multiplier * P
		exit when MULTIPLE > N;
		STATE(MULTIPLE):=COMPOSITE;
		MULTIPLE:=MULTIPLE + P;
	end loop;
 
    end if;
 
  end loop;
-- print out the sieve
  text_io.new_line;
  for line_nbr in 0..lines loop
	for col_nbr in 1 .. screen_width loop
		case STATE(line_nbr*screen_width+col_nbr) is
		when UNKNOWN  => text_io.put("u");
		when PRIME    => text_io.put("P");
		when COMPOSITE=> text_io.put(".");
		end case;
	end loop;
	text_io.new_line;
  end loop;
 
end PRIMES;