BigInteger inverse Mod - Java java.math

Java examples for java.math:BigInteger

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Description

BigInteger inverse Mod

Demo Code

/*// ww w. j a  v  a  2 s. c  o 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 {
    static BigInteger inverseMod(BigInteger a, BigInteger b) {
        BigInteger b0 = b, t, q;
        BigInteger x0 = BigInteger.ZERO, x1 = BigInteger.ONE;
        if (b.equals(BigInteger.ONE))
            return BigInteger.ONE;
        while (a.subtract(BigInteger.ONE).signum() > 0) {
            q = a.divide(b);
            t = b;
            b = a.mod(b);
            a = t;
            t = x0;
            x0 = x1.subtract(q.multiply(x0));
            x1 = t;
        }
        if (x1.signum() < 0)
            x1 = x1.add(b0);
        return x1;
    }
}

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