ASCII85Decode.java :  » PDF » PDF-Renderer » com » sun » pdfview » decode » Java Open Source

/*
 * $Id: ASCII85Decode.java,v 1.2 2007/12/20 18:33:33 rbair 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 '~&gt;'.
     *
     * @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();
    }

}