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


: prime? ( n -- f )
        dup 2 < if      drop false
    else dup 2 = if      drop true
    else dup 1 and 0= if drop false
    else 3
        begin 2dup dup * >=
        while 2dup mod 0=
              if       2drop false exit
              then 2 +
        repeat         2drop true
    then then then ;