1 /*
   2  * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   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
   7  * published by the Free Software Foundation.
   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
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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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 import java.math.BigInteger;
  31 
  32 public class ModInvTime {
  33     public static void main(String[] args) throws InterruptedException {
  34         BigInteger prime = new BigInteger("39402006196394479212279040100143613805079739270465446667946905279627659399113263569398956308152294913554433653942643");
  35         BigInteger s = new BigInteger("9552729729729327851382626410162104591956625415831952158766936536163093322096473638446154604799898109762512409920799");
  36         System.out.format("int length: %d, modulus length: %d%n",
  37             s.bitLength(), prime.bitLength());
  38 
  39         System.out.println("Computing modular inverse ...");
  40         BigInteger mi = s.modInverse(prime);
  41         System.out.format("Modular inverse: %s%n", mi);
  42         check(s, prime, mi);
  43 
  44         BigInteger ns = s.negate();
  45         BigInteger nmi = ns.modInverse(prime);
  46         System.out.format("Modular inverse of negation: %s%n", nmi);
  47         check(ns, prime, nmi);
  48     }
  49 
  50     public static void check(BigInteger val, BigInteger mod, BigInteger inv) {
  51         BigInteger r = inv.multiply(val).remainder(mod);
  52         if (r.signum() == -1)
  53             r = r.add(mod);
  54         if (!r.equals(BigInteger.ONE))
  55             throw new RuntimeException("Numerically incorrect modular inverse");
  56     }
  57 }