BigInteger euler Criterion - Java java.math

Java examples for java.math:BigInteger

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Description

BigInteger euler Criterion

Demo Code

/*//from www .  ja v a2s. co m
 * Copyright 2013 Valentyn Kolesnikov
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
//package com.java2s;

import java.math.BigInteger;

public class Main {
    public static final BigInteger TWO = new BigInteger("2");

    static int eulerCriterion(BigInteger p, BigInteger a) {
        BigInteger exponent = (p.subtract(BigInteger.ONE)).divide(TWO);
        BigInteger x = a.modPow(exponent, p);
        if (x.equals(BigInteger.ZERO) || x.equals(BigInteger.ONE)) {
            return x.intValue();
        }
        BigInteger y = x.add(BigInteger.ONE).mod(p);
        return (y.equals(BigInteger.ZERO)) ? -1 : 2;
    }
}

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