utility.java

《移动Agent技术》一书的所有章节源代码。

    }
    encodeRun(buffer, runValue, runLength, state);

    // We must save the final byte, if there is one, by padding
    // an extra zero.
    if (state[0] != 0) appendEncodedByte(buffer, (byte)0, state);

    return buffer.toString();
    }

    /**
     * Encode a run, possibly a degenerate run (of < 4 values).
     * @param length The length of the run; must be > 0 && <= 0xFFFF.
     */
    private static final void encodeRun(StringBuffer buffer, short value, int length) {
    if (length < 4) {
        for (int j=0; j<length; ++j) {
        if (value == (int) ESCAPE) buffer.append(ESCAPE);
        buffer.append((char) value);
        }
    }
    else {
        if (length == (int) ESCAPE) {
        if (value == (int) ESCAPE) buffer.append(ESCAPE);
        buffer.append((char) value);
        --length;
        }
        buffer.append(ESCAPE);
        buffer.append((char) length);
        buffer.append((char) value); // Don't need to escape this value
    }
    }

    /**
     * Encode a run, possibly a degenerate run (of < 4 values).
     * @param length The length of the run; must be > 0 && <= 0xFF.
     */
    private static final void encodeRun(StringBuffer buffer, byte value, int length,
                    byte[] state) {
    if (length < 4) {
        for (int j=0; j<length; ++j) {
        if (value == ESCAPE_BYTE) appendEncodedByte(buffer, ESCAPE_BYTE, state);
        appendEncodedByte(buffer, value, state);
        }
    }
    else {
        if (length == ESCAPE_BYTE) {
        if (value == ESCAPE_BYTE) appendEncodedByte(buffer, ESCAPE_BYTE, state);
        appendEncodedByte(buffer, value, state);
        --length;
        }
        appendEncodedByte(buffer, ESCAPE_BYTE, state);
        appendEncodedByte(buffer, (byte)length, state);
        appendEncodedByte(buffer, value, state); // Don't need to escape this value
    }
    }

    /**
     * Append a byte to the given StringBuffer, packing two bytes into each
     * character.  The state parameter maintains intermediary data between
     * calls.
     * @param state A two-element array, with state[0] == 0 if this is the
     * first byte of a pair, or state[0] != 0 if this is the second byte
     * of a pair, in which case state[1] is the first byte.
     */
    private static final void appendEncodedByte(StringBuffer buffer, byte value,
                        byte[] state) {
    if (state[0] != 0) {
        char c = (char) ((state[1] << 8) | (((int) value) & 0xFF));
        buffer.append(c);
        state[0] = 0;
    }
    else {
        state[0] = 1;
        state[1] = value;
    }
    }

    /**
     * Construct an array of shorts from a run-length encoded string.
     */
    static final short[] RLEStringToShortArray(String s) {
    int length = (((int) s.charAt(0)) << 16) | ((int) s.charAt(1));
    short[] array = new short[length];
    int ai = 0;
    for (int i=2; i<s.length(); ++i) {
        char c = s.charAt(i);
        if (c == ESCAPE) {
        c = s.charAt(++i);
        if (c == ESCAPE) array[ai++] = (short) c;
        else {
            int runLength = (int) c;
            short runValue = (short) s.charAt(++i);
            for (int j=0; j<runLength; ++j) array[ai++] = runValue;
        }
        }
        else {
        array[ai++] = (short) c;
        }
    }

    if (ai != length)
        throw new InternalError("Bad run-length encoded short array");

    return array;
    }

    /**
     * Construct an array of bytes from a run-length encoded string.
     */
    static final byte[] RLEStringToByteArray(String s) {
    int length = (((int) s.charAt(0)) << 16) | ((int) s.charAt(1));
    byte[] array = new byte[length];
    boolean nextChar = true;
    char c = 0;
    int node = 0;
    int runLength = 0;
    int i = 2;
    for (int ai=0; ai<length; ) {
        // This part of the loop places the next byte into the local
        // variable 'b' each time through the loop.  It keeps the
        // current character in 'c' and uses the boolean 'nextChar'
        // to see if we've taken both bytes out of 'c' yet.
        byte b;
        if (nextChar) {
        c = s.charAt(i++);
        b = (byte) (c >> 8);
        nextChar = false;
        }
        else {
        b = (byte) (c & 0xFF);
        nextChar = true;
        }

        // This part of the loop is a tiny state machine which handles
        // the parsing of the run-length encoding.  This would be simpler
        // if we could look ahead, but we can't, so we use 'node' to
        // move between three nodes in the state machine.
        switch (node) {
        case 0:
        // Normal idle node
        if (b == ESCAPE_BYTE) {
            node = 1;
        }
        else {
            array[ai++] = b;
        }
        break;
        case 1:
        // We have seen one ESCAPE_BYTE; we expect either a second
        // one, or a run length and value.
        if (b == ESCAPE_BYTE) {
            array[ai++] = ESCAPE_BYTE;
            node = 0;
        }
        else {
            runLength = b;
            // Interpret signed byte as unsigned
            if (runLength < 0) runLength += 0x100;
            node = 2;
        }
        break;
        case 2:
        // We have seen an ESCAPE_BYTE and length byte.  We interpret
        // the next byte as the value to be repeated.
        for (int j=0; j<runLength; ++j) array[ai++] = b;
        node = 0;
        break;
        }
    }

    if (node != 0)
        throw new InternalError("Bad run-length encoded byte array");

    if (i != s.length())
        throw new InternalError("Excess data in RLE byte array string");

    return array;
    }

    /**
     * Format a String for representation in a source file.  This includes
     * breaking it into lines escaping characters using octal notation
     * when necessary (control characters and double quotes).
     */
    static final String formatForSource(String s) {
    StringBuffer buffer = new StringBuffer();
    for (int i=0; i<s.length();) {
        if (i > 0) buffer.append("+\n");
        buffer.append("        \"");
        int count = 11;
        while (i<s.length() && count<80) {
        char c = s.charAt(i++);
        if (c < '\u0020' || c == '"') {
            // Represent control characters and the double quote
            // using octal notation; otherwise the string we form
            // won't compile, since Unicode escape sequences are
            // processed before tokenization.
            buffer.append('\\');
            buffer.append(HEX_DIGIT[(c & 0700) >> 6]); // HEX_DIGIT works for octal
            buffer.append(HEX_DIGIT[(c & 0070) >> 3]);
            buffer.append(HEX_DIGIT[(c & 0007)]);
            count += 4;
        }
        else if (c <= '\u007E') {
            buffer.append(c);
            count += 1;
        }
        else {
            buffer.append("\\u");
            buffer.append(HEX_DIGIT[(c & 0xF000) >> 12]);
            buffer.append(HEX_DIGIT[(c & 0x0F00) >> 8]);
            buffer.append(HEX_DIGIT[(c & 0x00F0) >> 4]);
            buffer.append(HEX_DIGIT[(c & 0x000F)]);
            count += 6;
        }
        }
        buffer.append('"');
    }
    return buffer.toString();
    }

    static final char[] HEX_DIGIT = {'0','1','2','3','4','5','6','7',
                     '8','9','A','B','C','D','E','F'};
}