Task

Write a boolean function that tells whether a given integer is prime.



Remember that   1   and all non-positive numbers are not prime.

Use trial division.

Even numbers greater than   2   may be eliminated right away.

A loop from   3   to   √ n    will suffice,   but other loops are allowed.



Related tasks

   count in factors
   prime decomposition
   AKS test for primes
   factors of an integer
   Sieve of Eratosthenes
   factors of a Mersenne number
   trial factoring of a Mersenne number
   partition an integer X into N primes
   sequence of primes by Trial Division


function Is_Prime(Item : Positive) return Boolean is
   Test : Natural;
begin
   if Item = 1 then
      return False;
   elsif Item = 2 then
      return True;
   elsif Item mod 2 = 0 then
      return False;
   else
      Test := 3;
      while Test <= Integer(Sqrt(Float(Item))) loop
         if Item mod Test = 0 then
            return False;
         end if;
         Test := Test + 2;
      end loop;
   end if;
   return True;
end Is_Prime;