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23 
24 /*
25  * @test
26  * @bug 8225603
27  * @summary Tests whether modInverse() completes in a reasonable time
28  * @run main/othervm ModInvTime
29  */
30 package test.java.math.BigInteger;
31 
32 import java.math.BigInteger;
33 
34 public class ModInvTime {
main(String[] args)35     public static void main(String[] args) throws InterruptedException {
36         BigInteger prime = new BigInteger("39402006196394479212279040100143613805079739270465446667946905279627659399113263569398956308152294913554433653942643");
37         BigInteger s = new BigInteger("9552729729729327851382626410162104591956625415831952158766936536163093322096473638446154604799898109762512409920799");
38         System.out.format("int length: %d, modulus length: %d%n",
39             s.bitLength(), prime.bitLength());
40 
41         System.out.println("Computing modular inverse ...");
42         BigInteger mi = s.modInverse(prime);
43         System.out.format("Modular inverse: %s%n", mi);
44         check(s, prime, mi);
45 
46         BigInteger ns = s.negate();
47         BigInteger nmi = ns.modInverse(prime);
48         System.out.format("Modular inverse of negation: %s%n", nmi);
49         check(ns, prime, nmi);
50     }
51 
check(BigInteger val, BigInteger mod, BigInteger inv)52     public static void check(BigInteger val, BigInteger mod, BigInteger inv) {
53         BigInteger r = inv.multiply(val).remainder(mod);
54         if (r.signum() == -1)
55             r = r.add(mod);
56         if (!r.equals(BigInteger.ONE))
57             throw new RuntimeException("Numerically incorrect modular inverse");
58     }
59 }
60