miller rabin 求质数的java实现 浮云

通常java判断质数，只需用BigInteger.nextProbablePrime()方法就行了。这里记录miller rabin 的一种java实现。

public class MillerRabin{
 public static void main(String[] args) {
  int p = 7, p2 = p - 1;
  boolean flag = true;
  int k, i, j = 0;
  k = (int) (Math.log(p) / Math.log(2)) + 1;
  int a[], b[], c[];
  c = new int[5];// 用来生成5个检测数
  a = new int[k];
  b = a;

  // 把P转化为2进制
  for (i = 0; p2 > 0; i++) {
   a[i] = p2 % 2;
   p2 /= 2;
  }
  for (i--; i >= 0; j++, i--) {
   b[j] = a[i];
  }

  for (int r = 0; r < a.length; r++) {
   System.out.print(a[r]);
  }
  for (int m = 0; m < 5; m++) { // //5次WITNESS(a[i],P)测试P的素数
   c[m] = (int) (Math.random() * (p - 3)) + 2;
   System.out.println("\n" + c[m]);
   if (witness(c[m], p, b) == 0) {
    flag = false;
   }
  }

  if (flag)
   System.out.println("Prime! " + p);
  else
   System.out.println("not Prime! " + p);

 }

 private static int witness(int a, int n, int[] b) {
  int x, k;
  int d = 1;
  k = b.length - 1;
  for (int m = k; m >= 0; m--) {
   x = (int) d;
   d = (d * a) % n;
   if ((d == 1) && (x != 1) && (x != n - 1))
    return 1;
   if (b[m] == 1)
    d = (d * a) % n;
  }
  if (d != 1){
   System.out.println("a:"+a+" n:"+n);
   return 0;
  }
  return 1;
 }
 
 public static void witness(int t) {
  BigInteger bi = new BigInteger(""+(t-1)+"");
  if(bi.nextProbablePrime().intValue()==t){
   System.out.println(t+" is prime!");
  }else{
   System.out.println(t+" is  not prime!");
  }
 }
}