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JCIFS is an Open Source client library that implements the CIFS/SMB networking protocol in 100% Java
There is a newer version: 2.1.39
/* Encodes and decodes to and from Base64 notation.
 * Copyright (C) 2003 "Eric Glass" 
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package jcifs.util;

public class Base64 {

    private static final String ALPHABET =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    /**
     * Base-64 encodes the supplied block of data.  Line wrapping is not
     * applied on output.
     *
     * @param bytes The block of data that is to be Base-64 encoded.
     * @return A String containing the encoded data.
     */
    public static String encode(byte[] bytes) {
        int length = bytes.length;
        if (length == 0) return "";
        StringBuffer buffer =
                new StringBuffer((int) Math.ceil((double) length / 3d) * 4);
        int remainder = length % 3;
        length -= remainder;
        int block;
        int i = 0;
        while (i < length) {
            block = ((bytes[i++] & 0xff) << 16) | ((bytes[i++] & 0xff) << 8) |
                    (bytes[i++] & 0xff);
            buffer.append(ALPHABET.charAt(block >>> 18));
            buffer.append(ALPHABET.charAt((block >>> 12) & 0x3f));
            buffer.append(ALPHABET.charAt((block >>> 6) & 0x3f));
            buffer.append(ALPHABET.charAt(block & 0x3f));
        }
        if (remainder == 0) return buffer.toString();
        if (remainder == 1) {
            block = (bytes[i] & 0xff) << 4;
            buffer.append(ALPHABET.charAt(block >>> 6));
            buffer.append(ALPHABET.charAt(block & 0x3f));
            buffer.append("==");
            return buffer.toString();
        }
        block = (((bytes[i++] & 0xff) << 8) | ((bytes[i]) & 0xff)) << 2;
        buffer.append(ALPHABET.charAt(block >>> 12));
        buffer.append(ALPHABET.charAt((block >>> 6) & 0x3f));
        buffer.append(ALPHABET.charAt(block & 0x3f));
        buffer.append("=");
        return buffer.toString();
    }

    /**
     * Decodes the supplied Base-64 encoded string.
     *
     * @param string The Base-64 encoded string that is to be decoded.
     * @return A byte[] containing the decoded data block.
     */
    public static byte[] decode(String string) {
        int length = string.length();
        if (length == 0) return new byte[0];
        int pad = (string.charAt(length - 2) == '=') ? 2 :
                (string.charAt(length - 1) == '=') ? 1 : 0;
        int size = length * 3 / 4 - pad;
        byte[] buffer = new byte[size];
        int block;
        int i = 0;
        int index = 0;
        while (i < length) {
            block = (ALPHABET.indexOf(string.charAt(i++)) & 0xff) << 18 |
                    (ALPHABET.indexOf(string.charAt(i++)) & 0xff) << 12 |
                    (ALPHABET.indexOf(string.charAt(i++)) & 0xff) << 6 |
                    (ALPHABET.indexOf(string.charAt(i++)) & 0xff);
            buffer[index++] = (byte) (block >>> 16);
            if (index < size) buffer[index++] = (byte) ((block >>> 8) & 0xff);
            if (index < size) buffer[index++] = (byte) (block & 0xff);
        }
        return buffer;
    }

}