/* * $Id: ASCII85Decoder.java,v 1.1 2011/03/24 20:20:40 lavoiale 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.spectotechnologies.imageio.plugins.eps.util; import java.io.ByteArrayOutputStream; import java.nio.ByteBuffer; import javax.imageio.IIOException; /** * decode ASCII85 text into a byte array. * @author Mike Wessler */ public class ASCII85Decoder { private ByteBuffer m_oBuffer; /** * initialize the decoder with byte buffer in ASCII85 format */ private ASCII85Decoder(ByteBuffer buf) { m_oBuffer = 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(m_oBuffer.remaining() > 0) { char c = (char) m_oBuffer.get(); if(!Character.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 IIOException { // 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 IIOException("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 IIOException("Inappropriate 'z' in ASCII85Decode"); } } else { throw new IIOException("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 IIOException { // start from the beginning of the data m_oBuffer.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. *
* 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 * @return the decoded bytes */ public static ByteBuffer decode(ByteBuffer buf) throws IIOException { ASCII85Decoder me = new ASCII85Decoder(buf); return me.decode(); } }