Java BigInteger Calculate getNRightmostBits(final BigInteger in, final int n)

Description

Returns a BigInteger with the n rightmost bits of in.

License

Open Source License

Parameter

Parameter	Description
in	the BigInteger of which the n rightmost bits are of interest.
n	the number of bits from the right of in that are of interest (n >= 0, and probably n <= in.bitLength()).

Return

a BigInteger with the BTREE rightmost bits of in.

Declaration

public static BigInteger getNRightmostBits(final BigInteger in, final int n) 

Method Source Code

//package com.java2s;
/*/*from   w  w  w .j a  v a2  s.c o m*/
 * Copyright (c) 2005-2011 KOM - Multimedia Communications Lab
 *
 * This file is part of PeerfactSim.KOM.
 * 
 * PeerfactSim.KOM is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * any later version.
 * 
 * PeerfactSim.KOM 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 for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with PeerfactSim.KOM.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

import java.math.BigInteger;

public class Main {
    /**
     * Returns a BigInteger with the <code>n</code> rightmost bits of
     * <code>in</code>.
     * 
     * @param in
     *            the BigInteger of which the n rightmost bits are of interest.
     * @param n
     *            the number of bits from the right of in that are of interest
     *            (n &gt;= 0, and probably n &lt;= in.bitLength()).
     * 
     * @return a BigInteger with the BTREE rightmost bits of <code>in</code>.
     */
    public static BigInteger getNRightmostBits(final BigInteger in, final int n) {
        // make sure only the last n bits are set
        final BigInteger mask = BigInteger.valueOf(2).pow(n).subtract(BigInteger.ONE);
        // BigInteger mask = BigInteger.valueOf(Math.round(Math.pow(2, n)) - 1);
        return in.and(mask);

        /*
         * TODO: This code does not work (because of sign extension??)
         * BigInteger negMask = BigInteger.ONE.shiftLeft(n); return
         * in.andNot(negMask);
         */
    }
}

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