/*
* $Id: ASCII85Decode.java,v 1.3 2009-02-22 00:52:35 tomoke Exp $
*
* Copyright 2004 Sun Microsystems, Inc., 4150 Network Circle,
* Santa Clara, California 95054, U.S.A. All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package com.sun.pdfview.decode;
import java.io.ByteArrayOutputStream;
import java.nio.ByteBuffer;
import com.sun.pdfview.PDFFile;
import com.sun.pdfview.PDFObject;
import com.sun.pdfview.PDFParseException;
/**
* decode ASCII85 text into a byte array.
*
* @author Mike Wessler
*/
public class ASCII85Decode {
private ByteBuffer buf;
/**
* initialize the decoder with byte buffer in ASCII85 format
*/
private ASCII85Decode(ByteBuffer buf) {
this.buf = buf;
}
/**
* get the next character from the input.
* @return the next character, or -1 if at end of stream
*/
private int nextChar() {
// skip whitespace
// returns next character, or -1 if end of stream
while (buf.remaining() > 0) {
char c = (char) buf.get();
if (!PDFFile.isWhiteSpace(c)) {
return c;
}
}
// EOF reached
return -1;
}
/**
* decode the next five ASCII85 characters into up to four decoded
* bytes. Return false when finished, or true otherwise.
*
* @param baos the ByteArrayOutputStream to write output to, set to the
* correct position
* @return false when finished, or true otherwise.
*/
private boolean decode5(ByteArrayOutputStream baos)
throws PDFParseException {
// stream ends in ~>
int[] five = new int[5];
int i;
for (i = 0; i < 5; i++) {
five[i] = nextChar();
if (five[i] == '~') {
if (nextChar() == '>') {
break;
} else {
throw new PDFParseException("Bad character in ASCII85Decode: not ~>");
}
} else if (five[i] >= '!' && five[i] <= 'u') {
five[i] -= '!';
} else if (five[i] == 'z') {
if (i == 0) {
five[i] = 0;
i = 4;
} else {
throw new PDFParseException("Inappropriate 'z' in ASCII85Decode");
}
} else {
throw new PDFParseException("Bad character in ASCII85Decode: " + five[i] + " (" + (char) five[i] + ")");
}
}
if (i > 0) {
i -= 1;
}
int value =
five[0] * 85 * 85 * 85 * 85 +
five[1] * 85 * 85 * 85 +
five[2] * 85 * 85 +
five[3] * 85 +
five[4];
for (int j = 0; j < i; j++) {
int shift = 8 * (3 - j);
baos.write((byte) ((value >> shift) & 0xff));
}
return (i == 4);
}
/**
* decode the bytes
* @return the decoded bytes
*/
private ByteBuffer decode() throws PDFParseException {
// start from the beginning of the data
buf.rewind();
// allocate the output buffer
ByteArrayOutputStream baos = new ByteArrayOutputStream();
// decode the bytes
while (decode5(baos)) {
}
return ByteBuffer.wrap(baos.toByteArray());
}
/**
* decode an array of bytes in ASCII85 format.
* <p>
* In ASCII85 format, every 5 characters represents 4 decoded
* bytes in base 85. The entire stream can contain whitespace,
* and ends in the characters '~>'.
*
* @param buf the encoded ASCII85 characters in a byte buffer
* @param params parameters to the decoder (ignored)
* @return the decoded bytes
*/
public static ByteBuffer decode(ByteBuffer buf, PDFObject params)
throws PDFParseException {
ASCII85Decode me = new ASCII85Decode(buf);
return me.decode();
}
}