Returns the closest power-of-two number less than or equal to x. - Java java.lang

Java examples for java.lang:double Array

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Description

Returns the closest power-of-two number less than or equal to x.

Demo Code

/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1/*from   w  w w.  j av a  2s.c  o m*/
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Parallel Colt.
 *
 * The Initial Developer of the Original Code is
 * Piotr Wendykier, Emory University.
 * Portions created by the Initial Developer are Copyright (C) 2007-2009
 * the Initial Developer. All Rights Reserved.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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//package com.java2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        int x = 2;
        System.out.println(prevPow2(x));
    }

    /**
     * Returns the closest power-of-two number less than or equal to x.
     * 
     * @param x
     * @return the closest power-of-two number less then or equal to x
     */
    public static int prevPow2(int x) {
        if (x < 1)
            throw new IllegalArgumentException(
                    "x must be greater or equal 1");
        return (int) Math.pow(2, Math.floor(Math.log(x) / Math.log(2)));
    }
}

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