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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 robust character encoder. The encoder is designed
   34    * to convert binary data into printable characters. The characters are
   35    * assumed to exist but they are not assumed to be ASCII, the complete set
   36    * is 0-9, A-Z, a-z, "(", and ")".
   37    *
   38    * The basic encoding unit is a 3 character atom. It encodes two bytes
   39    * of data. Bytes are encoded into a 64 character set, the characters
   40    * were chosen specifically because they appear in all codesets.
   41    * We don't care what their numerical equivalent is because
   42    * we use a character array to map them. This is like UUencoding
   43    * with the dependency on ASCII removed.
   44    *
   45    * The three chars that make up an atom are encoded as follows:
   46    * <pre>
   47    *      00xxxyyy 00axxxxx 00byyyyy
   48    *      00 = leading zeros, all values are 0 - 63
   49    *      xxxyyy - Top 3 bits of X, Top 3 bits of Y
   50    *      axxxxx - a = X parity bit, xxxxx lower 5 bits of X
   51    *      byyyyy - b = Y parity bit, yyyyy lower 5 bits of Y
   52    * </pre>
   53    *
   54    * The atoms are arranged into lines suitable for inclusion into an
   55    * email message or text file. The number of bytes that are encoded
   56    * per line is 48 which keeps the total line length  under 80 chars)
   57    *
   58    * Each line has the form(
   59    * <pre>
   60    *  *(LLSS)(DDDD)(DDDD)(DDDD)...(CRC)
   61    *  Where each (xxx) represents a three character atom.
   62    *  (LLSS) - 8 bit length (high byte), and sequence number
   63    *           modulo 256;
   64    *  (DDDD) - Data byte atoms, if length is odd, last data
   65    *           atom has (DD00) (high byte data, low byte 0)
   66    *  (CRC)  - 16 bit CRC for the line, includes length,
   67    *           sequence, and all data bytes. If there is a
   68    *           zero pad byte (odd length) it is _NOT_
   69    *           included in the CRC.
   70    * </pre>
   71    *
   72    * @author      Chuck McManis
   73    * @see         CharacterEncoder
   74    * @see         UCDecoder
   75    */
   76   public class UCEncoder extends CharacterEncoder {
   77   
   78       /** this clase encodes two bytes per atom */
   79       protected int bytesPerAtom() {
   80           return (2);
   81       }
   82   
   83       /** this class encodes 48 bytes per line */
   84       protected int bytesPerLine() {
   85           return (48);
   86       }
   87   
   88       /* this is the UCE mapping of 0-63 to characters .. */
   89       private final static byte map_array[] = {
   90           //     0         1         2         3         4         5         6         7
   91           (byte)'0',(byte)'1',(byte)'2',(byte)'3',(byte)'4',(byte)'5',(byte)'6',(byte)'7', // 0
   92           (byte)'8',(byte)'9',(byte)'A',(byte)'B',(byte)'C',(byte)'D',(byte)'E',(byte)'F', // 1
   93           (byte)'G',(byte)'H',(byte)'I',(byte)'J',(byte)'K',(byte)'L',(byte)'M',(byte)'N', // 2
   94           (byte)'O',(byte)'P',(byte)'Q',(byte)'R',(byte)'S',(byte)'T',(byte)'U',(byte)'V', // 3
   95           (byte)'W',(byte)'X',(byte)'Y',(byte)'Z',(byte)'a',(byte)'b',(byte)'c',(byte)'d', // 4
   96           (byte)'e',(byte)'f',(byte)'g',(byte)'h',(byte)'i',(byte)'j',(byte)'k',(byte)'l', // 5
   97           (byte)'m',(byte)'n',(byte)'o',(byte)'p',(byte)'q',(byte)'r',(byte)'s',(byte)'t', // 6
   98           (byte)'u',(byte)'v',(byte)'w',(byte)'x',(byte)'y',(byte)'z',(byte)'(',(byte)')'  // 7
   99       };
  100   
  101       private int sequence;
  102       private byte tmp[] = new byte[2];
  103       private CRC16 crc = new CRC16();
  104   
  105       /**
  106        * encodeAtom - take two bytes and encode them into the correct
  107        * three characters. If only one byte is to be encoded, the other
  108        * must be zero. The padding byte is not included in the CRC computation.
  109        */
  110       protected void encodeAtom(OutputStream outStream, byte data[], int offset, int len) throws IOException
  111       {
  112           int     i;
  113           int     p1, p2; // parity bits
  114           byte    a, b;
  115   
  116           a = data[offset];
  117           if (len == 2) {
  118               b = data[offset+1];
  119           } else {
  120               b = 0;
  121           }
  122           crc.update(a);
  123           if (len == 2) {
  124               crc.update(b);
  125           }
  126           outStream.write(map_array[((a >>> 2) & 0x38) + ((b >>> 5) & 0x7)]);
  127           p1 = 0; p2 = 0;
  128           for (i = 1; i < 256; i = i * 2) {
  129               if ((a & i) != 0) {
  130                   p1++;
  131               }
  132               if ((b & i) != 0) {
  133                   p2++;
  134               }
  135           }
  136           p1 = (p1 & 1) * 32;
  137           p2 = (p2 & 1) * 32;
  138           outStream.write(map_array[(a & 31) + p1]);
  139           outStream.write(map_array[(b & 31) + p2]);
  140           return;
  141       }
  142   
  143       /**
  144        * Each UCE encoded line starts with a prefix of '*[XXX]', where
  145        * the sequence number and the length are encoded in the first
  146        * atom.
  147        */
  148       protected void encodeLinePrefix(OutputStream outStream, int length) throws IOException {
  149           outStream.write('*');
  150           crc.value = 0;
  151           tmp[0] = (byte) length;
  152           tmp[1] = (byte) sequence;
  153           sequence = (sequence + 1) & 0xff;
  154           encodeAtom(outStream, tmp, 0, 2);
  155       }
  156   
  157   
  158       /**
  159        * each UCE encoded line ends with YYY and encoded version of the
  160        * 16 bit checksum. The most significant byte of the check sum
  161        * is always encoded FIRST.
  162        */
  163       protected void encodeLineSuffix(OutputStream outStream) throws IOException {
  164           tmp[0] = (byte) ((crc.value >>> 8) & 0xff);
  165           tmp[1] = (byte) (crc.value & 0xff);
  166           encodeAtom(outStream, tmp, 0, 2);
  167           super.pStream.println();
  168       }
  169   
  170       /**
  171        * The buffer prefix code is used to initialize the sequence number
  172        * to zero.
  173        */
  174       protected void encodeBufferPrefix(OutputStream a) throws IOException {
  175           sequence = 0;
  176           super.encodeBufferPrefix(a);
  177       }
  178   }

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