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


int is_prime(unsigned int n)
{
	unsigned int p;
	if (!(n & 1) || n < 2 ) return n == 2;
 
	/* comparing p*p <= n can overflow */
	for (p = 3; p <= n/p; p += 2)
		if (!(n % p)) return 0;
	return 1;
}