Java BigInteger Calculate sqrt(BigInteger n)

Description

Computes the integer square root of a number.

License

Open Source License

Parameter

Parameter	Description
n	The number.

Return

The integer square root, i.e. the largest number whose square doesn't exceed n.

Declaration

public static BigInteger sqrt(BigInteger n) 

Method Source Code

//package com.java2s;
/*/* w  ww  .  j  av a2  s. c om*/
 * Redberry: symbolic tensor computations.
 *
 * Copyright (c) 2010-2013:
 *   Stanislav Poslavsky   <stvlpos@mail.ru>
 *   Bolotin Dmitriy       <bolotin.dmitriy@gmail.com>
 *
 * This file is part of Redberry.
 *
 * Redberry 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.
 *
 * Redberry 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 Redberry. If not, see <http://www.gnu.org/licenses/>.
 */

import java.math.BigInteger;

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

    /**
     * Computes the integer square root of a number.
     *
     * @param n The number.
     * @return The integer square root, i.e. the largest number whose square
     *         doesn't exceed n.
     */
    public static BigInteger sqrt(BigInteger n) {
        if (n.signum() >= 0) {
            final int bitLength = n.bitLength();
            BigInteger root = BigInteger.ONE.shiftLeft(bitLength / 2);

            while (!isSqrtXXX(n, root))
                root = root.add(n.divide(root)).divide(TWO);
            return root;
        } else
            throw new ArithmeticException("square root of negative number");
    }

    private static boolean isSqrtXXX(BigInteger n, BigInteger root) {
        final BigInteger lowerBound = root.pow(2);
        final BigInteger upperBound = root.add(BigInteger.ONE).pow(2);
        return lowerBound.compareTo(n) <= 0 && n.compareTo(upperBound) < 0;
    }
}

Related

1. shift(BigInteger integer, int distance)
2. shiftLeft(final BigInteger register, final BigInteger input, final int n)
3. split(BigInteger maxValue, int numberOfSplits)
4. splitBigInt(BigInteger value, int n)
5. splitFloat(BigInteger rawFloat, int signWidth, int exponentWidth, int mantissaWidth)
6. sqrt(BigInteger n)
7. sqrt(BigInteger n)
8. square(BigInteger x)
9. subArray(BigInteger[] input, int start, int end)