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


const func boolean: isPrime (in integer: number) is func
  result
    var boolean: prime is FALSE;
  local
    var integer: upTo is 0;
    var integer: testNum is 3;
  begin
    if number = 2 then
      prime := TRUE;
    elsif odd(number) and number > 2 then
      upTo := sqrt(number);
      while number rem testNum <> 0 and testNum <= upTo do
        testNum +:= 2;
      end while;
      prime := testNum > upTo;
    end if;
  end func;