/*
* Copyright 1995-1997 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the LICENSE file that accompanied this code.
*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*/
package sun.misc;
import java.io.OutputStream;
import java.io.InputStream;
import java.io.PrintStream;
import java.io.IOException;
/**
* This class implements a robust character encoder. The encoder is designed
* to convert binary data into printable characters. The characters are
* assumed to exist but they are not assumed to be ASCII, the complete set
* is 0-9, A-Z, a-z, "(", and ")".
*
* The basic encoding unit is a 3 character atom. It encodes two bytes
* of data. Bytes are encoded into a 64 character set, the characters
* were chosen specifically because they appear in all codesets.
* We don't care what their numerical equivalent is because
* we use a character array to map them. This is like UUencoding
* with the dependency on ASCII removed.
*
* The three chars that make up an atom are encoded as follows:
* <pre>
* 00xxxyyy 00axxxxx 00byyyyy
* 00 = leading zeros, all values are 0 - 63
* xxxyyy - Top 3 bits of X, Top 3 bits of Y
* axxxxx - a = X parity bit, xxxxx lower 5 bits of X
* byyyyy - b = Y parity bit, yyyyy lower 5 bits of Y
* </pre>
*
* The atoms are arranged into lines suitable for inclusion into an
* email message or text file. The number of bytes that are encoded
* per line is 48 which keeps the total line length under 80 chars)
*
* Each line has the form(
* <pre>
* *(LLSS)(DDDD)(DDDD)(DDDD)...(CRC)
* Where each (xxx) represents a three character atom.
* (LLSS) - 8 bit length (high byte), and sequence number
* modulo 256;
* (DDDD) - Data byte atoms, if length is odd, last data
* atom has (DD00) (high byte data, low byte 0)
* (CRC) - 16 bit CRC for the line, includes length,
* sequence, and all data bytes. If there is a
* zero pad byte (odd length) it is _NOT_
* included in the CRC.
* </pre>
*
* @author Chuck McManis
* @see CharacterEncoder
* @see UCDecoder
*/
public class UCEncoder extends CharacterEncoder {
/** this clase encodes two bytes per atom */
protected int bytesPerAtom() {
return (2);
}
/** this class encodes 48 bytes per line */
protected int bytesPerLine() {
return (48);
}
/* this is the UCE mapping of 0-63 to characters .. */
private final static byte map_array[] = {
// 0 1 2 3 4 5 6 7
(byte)'0',(byte)'1',(byte)'2',(byte)'3',(byte)'4',(byte)'5',(byte)'6',(byte)'7', // 0
(byte)'8',(byte)'9',(byte)'A',(byte)'B',(byte)'C',(byte)'D',(byte)'E',(byte)'F', // 1
(byte)'G',(byte)'H',(byte)'I',(byte)'J',(byte)'K',(byte)'L',(byte)'M',(byte)'N', // 2
(byte)'O',(byte)'P',(byte)'Q',(byte)'R',(byte)'S',(byte)'T',(byte)'U',(byte)'V', // 3
(byte)'W',(byte)'X',(byte)'Y',(byte)'Z',(byte)'a',(byte)'b',(byte)'c',(byte)'d', // 4
(byte)'e',(byte)'f',(byte)'g',(byte)'h',(byte)'i',(byte)'j',(byte)'k',(byte)'l', // 5
(byte)'m',(byte)'n',(byte)'o',(byte)'p',(byte)'q',(byte)'r',(byte)'s',(byte)'t', // 6
(byte)'u',(byte)'v',(byte)'w',(byte)'x',(byte)'y',(byte)'z',(byte)'(',(byte)')' // 7
};
private int sequence;
private byte tmp[] = new byte[2];
private CRC16 crc = new CRC16();
/**
* encodeAtom - take two bytes and encode them into the correct
* three characters. If only one byte is to be encoded, the other
* must be zero. The padding byte is not included in the CRC computation.
*/
protected void encodeAtom(OutputStream outStream, byte data[], int offset, int len) throws IOException
{
int i;
int p1, p2; // parity bits
byte a, b;
a = data[offset];
if (len == 2) {
b = data[offset+1];
} else {
b = 0;
}
crc.update(a);
if (len == 2) {
crc.update(b);
}
outStream.write(map_array[((a >>> 2) & 0x38) + ((b >>> 5) & 0x7)]);
p1 = 0; p2 = 0;
for (i = 1; i < 256; i = i * 2) {
if ((a & i) != 0) {
p1++;
}
if ((b & i) != 0) {
p2++;
}
}
p1 = (p1 & 1) * 32;
p2 = (p2 & 1) * 32;
outStream.write(map_array[(a & 31) + p1]);
outStream.write(map_array[(b & 31) + p2]);
return;
}
/**
* Each UCE encoded line starts with a prefix of '*[XXX]', where
* the sequence number and the length are encoded in the first
* atom.
*/
protected void encodeLinePrefix(OutputStream outStream, int length) throws IOException {
outStream.write('*');
crc.value = 0;
tmp[0] = (byte) length;
tmp[1] = (byte) sequence;
sequence = (sequence + 1) & 0xff;
encodeAtom(outStream, tmp, 0, 2);
}
/**
* each UCE encoded line ends with YYY and encoded version of the
* 16 bit checksum. The most significant byte of the check sum
* is always encoded FIRST.
*/
protected void encodeLineSuffix(OutputStream outStream) throws IOException {
tmp[0] = (byte) ((crc.value >>> 8) & 0xff);
tmp[1] = (byte) (crc.value & 0xff);
encodeAtom(outStream, tmp, 0, 2);
super.pStream.println();
}
/**
* The buffer prefix code is used to initialize the sequence number
* to zero.
*/
protected void encodeBufferPrefix(OutputStream a) throws IOException {
sequence = 0;
super.encodeBufferPrefix(a);
}
}