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    1   /*
    2    * Copyright (c) 1995, 1997, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   package sun.misc;
   26   
   27   import java.io.OutputStream;
   28   import java.io.InputStream;
   29   import java.io.PrintStream;
   30   import java.io.IOException;
   31   
   32   /**
   33    * This class implements a BASE64 Character encoder as specified in RFC1521.
   34    * This RFC is part of the MIME specification as published by the Internet
   35    * Engineering Task Force (IETF). Unlike some other encoding schemes there
   36    * is nothing in this encoding that indicates
   37    * where a buffer starts or ends.
   38    *
   39    * This means that the encoded text will simply start with the first line
   40    * of encoded text and end with the last line of encoded text.
   41    *
   42    * @author      Chuck McManis
   43    * @see         CharacterEncoder
   44    * @see         BASE64Decoder
   45    */
   46   
   47   public class BASE64Encoder extends CharacterEncoder {
   48   
   49       /** this class encodes three bytes per atom. */
   50       protected int bytesPerAtom() {
   51           return (3);
   52       }
   53   
   54       /**
   55        * this class encodes 57 bytes per line. This results in a maximum
   56        * of 57/3 * 4 or 76 characters per output line. Not counting the
   57        * line termination.
   58        */
   59       protected int bytesPerLine() {
   60           return (57);
   61       }
   62   
   63       /** This array maps the characters to their 6 bit values */
   64       private final static char pem_array[] = {
   65           //       0   1   2   3   4   5   6   7
   66                   'A','B','C','D','E','F','G','H', // 0
   67                   'I','J','K','L','M','N','O','P', // 1
   68                   'Q','R','S','T','U','V','W','X', // 2
   69                   'Y','Z','a','b','c','d','e','f', // 3
   70                   'g','h','i','j','k','l','m','n', // 4
   71                   'o','p','q','r','s','t','u','v', // 5
   72                   'w','x','y','z','0','1','2','3', // 6
   73                   '4','5','6','7','8','9','+','/'  // 7
   74           };
   75   
   76       /**
   77        * encodeAtom - Take three bytes of input and encode it as 4
   78        * printable characters. Note that if the length in len is less
   79        * than three is encodes either one or two '=' signs to indicate
   80        * padding characters.
   81        */
   82       protected void encodeAtom(OutputStream outStream, byte data[], int offset, int len)
   83           throws IOException {
   84           byte a, b, c;
   85   
   86           if (len == 1) {
   87               a = data[offset];
   88               b = 0;
   89               c = 0;
   90               outStream.write(pem_array[(a >>> 2) & 0x3F]);
   91               outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
   92               outStream.write('=');
   93               outStream.write('=');
   94           } else if (len == 2) {
   95               a = data[offset];
   96               b = data[offset+1];
   97               c = 0;
   98               outStream.write(pem_array[(a >>> 2) & 0x3F]);
   99               outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
  100               outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
  101               outStream.write('=');
  102           } else {
  103               a = data[offset];
  104               b = data[offset+1];
  105               c = data[offset+2];
  106               outStream.write(pem_array[(a >>> 2) & 0x3F]);
  107               outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
  108               outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
  109               outStream.write(pem_array[c & 0x3F]);
  110           }
  111       }
  112   }

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