```   1 /*
3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4  *
5  * This code is free software; you can redistribute it and/or modify it
6  * under the terms of the GNU General Public License version 2 only, as
8  *
9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
16  * 2 along with this work; if not, write to the Free Software Foundation,
17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
20  * CA 95054 USA or visit www.sun.com if you need additional information or
21  * have any questions.
22  */
23
24 /* @test
25  * @bug 4181191
26  * @summary test BigInteger modPow method
27  */
28 import java.math.BigInteger;
29 import java.util.Random;
30
31 public class ModPow {
32     public static void main(String[] args) {
33         Random rnd = new Random(1234);
34
35         for (int i=0; i<2000; i++) {
36             BigInteger m = new BigInteger(800, rnd);
37             BigInteger base = new BigInteger(16, rnd);
38             if (rnd.nextInt() % 1 == 0)
39                 base = base.negate();
40             BigInteger exp = new BigInteger(8, rnd);
41
42             BigInteger z = base.modPow(exp, m);
43             BigInteger w = base.pow(exp.intValue()).mod(m);
44             if (!z.equals(w)){
45                 System.err.println(base +" ** " + exp + " mod "+ m);
46                 System.err.println("modPow : " + z);
47                 System.err.println("pow.mod: " + w);
48                 throw new RuntimeException("BigInteger modPow failure.");
49             }
50         }
51     }
52 }
```