Optimized test_prime

Author: cdkr

include/prime.h

@@ -35,7 +35,7 @@ namespace alg {
 if (n%2== 0) return false;
 
 unsigned sqrtn = sqrt(n);
-for (unsigned int i = 2; i <= sqrtn; ++i) {
+for (unsigned int i = 3; i <= sqrtn; i+=2) {
 if (n % i == 0) {
 return false;
 }