一种快速判断是否为质数的方法

public static boolean isprime(int x) ...{




if (x <= 7) ...{


if (x == 2 || x == 3 || x==5 || x == 7)


return true;


}


int c = 7;


if (x % 2 == 0)


return false;


if (x % 3 == 0)


return false;


if (x % 5 == 0)


return false;


int end = (int) Math.sqrt(x);




while (c <= end) ...{




if (x % c == 0) ...{


return false;


}


c += 4;




if (x % c == 0) ...{


return false;


}


c += 2;




if (x % c == 0) ...{


return false;


}


c += 4;




if (x % c == 0) ...{


return false;


}


c += 2;




if (x % c == 0) ...{


return false;


}


c += 4;




if (x % c == 0) ...{


return false;


}


c += 6;




if (x % c == 0) ...{


return false;


}


c += 2;




if (x % c == 0) ...{


return false;


}


c += 6;


}


return true;


}