/*
* @(#)UCEncoder.java 1.11 95/09/06 Chuck McManis
*
* Copyright (c) 1995 Sun Microsystems, Inc. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this software
* and its documentation for NON-COMMERCIAL purposes and without
* fee is hereby granted provided that this copyright notice
* appears in all copies. Please refer to the file "copyright.html"
* for further important copyright and licensing information.
*
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
* THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
* TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
* ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
* DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
*/
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>
*
* @version 1.11, 06 Sep 1995
* @author Chuck McManis
* @see CharacterEncoder
* @see UCDecoder
*/
public class UCEncoder extends CharacterEncoder {
/** this clase encodes two bytes per atom */
int bytesPerAtom() {
return (2);
}
/** this class encodes 48 bytes per line */
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
'0','1','2','3','4','5','6','7', // 0
'8','9','A','B','C','D','E','F', // 1
'G','H','I','J','K','L','M','N', // 2
'O','P','Q','R','S','T','U','V', // 3
'W','X','Y','Z','a','b','c','d', // 4
'e','f','g','h','i','j','k','l', // 5
'm','n','o','p','q','r','s','t', // 6
'u','v','w','x','y','z','(',')' // 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.
*/
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.
*/
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.
*/
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.
*/
void encodeBufferPrefix(OutputStream a) throws IOException {
sequence = 0;
super.encodeBufferPrefix(a);
}
}