Java BigInteger Reverse reverse(BigInteger x, int width)

Description

reverse

License

Open Source License

Declaration

public static BigInteger reverse(BigInteger x, int width) 

Method Source Code

//package com.java2s;
/*/*w ww .  jav a  2  s.  com*/
 Copyright (C) 2017, 2018 Bengt Martensson.

 This program 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 (at
 your option) any later version.

 This program 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
 this program. If not, see http://www.gnu.org/licenses/.
 */

import java.math.BigInteger;

public class Main {
    /**
     * Reverses the bits, living in a width-bit wide world.
     *
     * @param x data
     * @param width width in bits
     * @return bitreversed
     */

    public static long reverse(long x, int width) {
        long y = Long.reverse(x);
        if (width > 0)
            y >>>= Long.SIZE - width;
        return y;
    }

    public static BigInteger reverse(BigInteger x, int width) {
        try {
            if (width < Long.SIZE)
                return BigInteger
                        .valueOf(reverse(x.longValueExact(), width));
        } catch (ArithmeticException ex) {
        }

        // A very inefficient implementation, but executed quite seldomly
        StringBuilder str = new StringBuilder(x.toString(2));
        if (str.length() > width)
            str.delete(0, str.length() - width);
        else
            while (str.length() < width)
                str.insert(0, '0');
        str.reverse();
        return new BigInteger(str.toString(), 2);
    }
}

Related

1. reverse(BigInteger currentSum)
2. reverse(BigInteger n)