ModPow.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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/* @test
 * @bug 4181191
 * @summary test BigInteger modPow method
 */
import java.math.BigInteger;
import java.util.Random;

public class ModPow {
    public static void main(String[] args) {
        Random rnd = new Random(1234);

        for (int i=0; i<2000; i++) {
            BigInteger m = new BigInteger(800, rnd);
            BigInteger base = new BigInteger(16, rnd);
            if (rnd.nextInt() % 1 == 0)
                base = base.negate();
            BigInteger exp = new BigInteger(8, rnd);

            BigInteger z = base.modPow(exp, m);
            BigInteger w = base.pow(exp.intValue()).mod(m);
            if (!z.equals(w)){
                System.err.println(base +" ** " + exp + " mod "+ m);
                System.err.println("modPow : " + z);
                System.err.println("pow.mod: " + w);
                throw new RuntimeException("BigInteger modPow failure.");
            }
        }
    }
}