jdk/src/share/classes/sun/misc/UCEncoder.java
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/*
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 * Copyright (c) 1995, 1997, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.  Oracle designates this
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 * particular file as subject to the "Classpath" exception as provided
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 * by Oracle in the LICENSE file that accompanied this code.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 */
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package sun.misc;
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import java.io.OutputStream;
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import java.io.InputStream;
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import java.io.PrintStream;
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import java.io.IOException;
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/**
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 * This class implements a robust character encoder. The encoder is designed
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 * to convert binary data into printable characters. The characters are
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 * assumed to exist but they are not assumed to be ASCII, the complete set
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 * is 0-9, A-Z, a-z, "(", and ")".
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 *
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 * The basic encoding unit is a 3 character atom. It encodes two bytes
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 * of data. Bytes are encoded into a 64 character set, the characters
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 * were chosen specifically because they appear in all codesets.
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 * We don't care what their numerical equivalent is because
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 * we use a character array to map them. This is like UUencoding
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 * with the dependency on ASCII removed.
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 *
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 * The three chars that make up an atom are encoded as follows:
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 * <pre>
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 *      00xxxyyy 00axxxxx 00byyyyy
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 *      00 = leading zeros, all values are 0 - 63
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 *      xxxyyy - Top 3 bits of X, Top 3 bits of Y
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 *      axxxxx - a = X parity bit, xxxxx lower 5 bits of X
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 *      byyyyy - b = Y parity bit, yyyyy lower 5 bits of Y
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 * </pre>
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 *
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 * The atoms are arranged into lines suitable for inclusion into an
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 * email message or text file. The number of bytes that are encoded
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 * per line is 48 which keeps the total line length  under 80 chars)
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 *
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 * Each line has the form(
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 * <pre>
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 *  *(LLSS)(DDDD)(DDDD)(DDDD)...(CRC)
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 *  Where each (xxx) represents a three character atom.
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 *  (LLSS) - 8 bit length (high byte), and sequence number
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 *           modulo 256;
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 *  (DDDD) - Data byte atoms, if length is odd, last data
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 *           atom has (DD00) (high byte data, low byte 0)
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 *  (CRC)  - 16 bit CRC for the line, includes length,
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 *           sequence, and all data bytes. If there is a
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 *           zero pad byte (odd length) it is _NOT_
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 *           included in the CRC.
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 * </pre>
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 *
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 * @author      Chuck McManis
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 * @see         CharacterEncoder
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 * @see         UCDecoder
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 */
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public class UCEncoder extends CharacterEncoder {
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    /** this clase encodes two bytes per atom */
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    protected int bytesPerAtom() {
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        return (2);
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    }
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    /** this class encodes 48 bytes per line */
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    protected int bytesPerLine() {
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        return (48);
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    }
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    /* this is the UCE mapping of 0-63 to characters .. */
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    private final static byte map_array[] = {
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        //     0         1         2         3         4         5         6         7
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        (byte)'0',(byte)'1',(byte)'2',(byte)'3',(byte)'4',(byte)'5',(byte)'6',(byte)'7', // 0
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        (byte)'8',(byte)'9',(byte)'A',(byte)'B',(byte)'C',(byte)'D',(byte)'E',(byte)'F', // 1
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        (byte)'G',(byte)'H',(byte)'I',(byte)'J',(byte)'K',(byte)'L',(byte)'M',(byte)'N', // 2
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        (byte)'O',(byte)'P',(byte)'Q',(byte)'R',(byte)'S',(byte)'T',(byte)'U',(byte)'V', // 3
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        (byte)'W',(byte)'X',(byte)'Y',(byte)'Z',(byte)'a',(byte)'b',(byte)'c',(byte)'d', // 4
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        (byte)'e',(byte)'f',(byte)'g',(byte)'h',(byte)'i',(byte)'j',(byte)'k',(byte)'l', // 5
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        (byte)'m',(byte)'n',(byte)'o',(byte)'p',(byte)'q',(byte)'r',(byte)'s',(byte)'t', // 6
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        (byte)'u',(byte)'v',(byte)'w',(byte)'x',(byte)'y',(byte)'z',(byte)'(',(byte)')'  // 7
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    };
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    private int sequence;
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    private byte tmp[] = new byte[2];
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    private CRC16 crc = new CRC16();
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    /**
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     * encodeAtom - take two bytes and encode them into the correct
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     * three characters. If only one byte is to be encoded, the other
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     * must be zero. The padding byte is not included in the CRC computation.
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     */
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    protected void encodeAtom(OutputStream outStream, byte data[], int offset, int len) throws IOException
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    {
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        int     i;
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        int     p1, p2; // parity bits
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        byte    a, b;
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        a = data[offset];
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        if (len == 2) {
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            b = data[offset+1];
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        } else {
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            b = 0;
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        }
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        crc.update(a);
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        if (len == 2) {
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            crc.update(b);
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        }
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        outStream.write(map_array[((a >>> 2) & 0x38) + ((b >>> 5) & 0x7)]);
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        p1 = 0; p2 = 0;
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        for (i = 1; i < 256; i = i * 2) {
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            if ((a & i) != 0) {
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                p1++;
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            }
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            if ((b & i) != 0) {
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                p2++;
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            }
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        }
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        p1 = (p1 & 1) * 32;
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        p2 = (p2 & 1) * 32;
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        outStream.write(map_array[(a & 31) + p1]);
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        outStream.write(map_array[(b & 31) + p2]);
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        return;
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    }
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    /**
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     * Each UCE encoded line starts with a prefix of '*[XXX]', where
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     * the sequence number and the length are encoded in the first
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     * atom.
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     */
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    protected void encodeLinePrefix(OutputStream outStream, int length) throws IOException {
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        outStream.write('*');
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        crc.value = 0;
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        tmp[0] = (byte) length;
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        tmp[1] = (byte) sequence;
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        sequence = (sequence + 1) & 0xff;
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        encodeAtom(outStream, tmp, 0, 2);
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    }
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    /**
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     * each UCE encoded line ends with YYY and encoded version of the
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     * 16 bit checksum. The most significant byte of the check sum
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     * is always encoded FIRST.
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     */
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    protected void encodeLineSuffix(OutputStream outStream) throws IOException {
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        tmp[0] = (byte) ((crc.value >>> 8) & 0xff);
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        tmp[1] = (byte) (crc.value & 0xff);
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        encodeAtom(outStream, tmp, 0, 2);
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        super.pStream.println();
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    }
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    /**
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     * The buffer prefix code is used to initialize the sequence number
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     * to zero.
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     */
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    protected void encodeBufferPrefix(OutputStream a) throws IOException {
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        sequence = 0;
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        super.encodeBufferPrefix(a);
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    }
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}