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FreeHEP extension to the java.io library
There is a newer version: 2.2.2
// Copyright 2001-2009, FreeHEP.
package org.freehep.util.io;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * The ASCII85InputStream decodes ASCII base-85 encoded data. The exact
 * definition of ASCII base-85 encoding can be found in the PostScript Language
 * Reference (3rd ed.) chapter 3.13.3. More info also on
 * http://en.wikipedia.org/wiki/Ascii85
 * 
 * @author Mark Donszelmann
 */
public class ASCII85InputStream extends DecodingInputStream implements ASCII85 {

	private boolean endReached;

	private int b[] = new int[4];

	private int bIndex;

	private int bLength;

	private int c[] = new int[5];

	private int lineNo;

	private int prev;

	private InputStream in;

	/**
	 * Create an ASCII85 Input Stream from given stream.
	 * 
	 * @param input
	 *            input to use
	 */
	public ASCII85InputStream(InputStream input) {
		super();
		in = input;
		bIndex = 0;
		bLength = 0;
		endReached = false;
		prev = -1;
		lineNo = 1;
	}

	@Override
	public int read() throws IOException {

		if (bIndex >= bLength) {
			if (endReached) {
				return -1;
			}
			bLength = readTuple();
			if (bLength < 0) {
				return -1;
			}
			bIndex = 0;
		}
		int a = b[bIndex];
		bIndex++;

		return a;
	}

	/**
	 * @return current line number
	 */
	public int getLineNo() {
		return lineNo;
	}

	private int readTuple() throws IOException, EncodingException {
		int cIndex = 0;
		int ch = -1;
		while ((!endReached) && (cIndex < 5)) {
			prev = ch;
			ch = in.read();
			switch (ch) {
			case -1:
				throw new EncodingException(
						"ASCII85InputStream: missing '~>' at end of stream");
			case 'z':
				if (cIndex != 0) {
					throw new EncodingException(
							"ASCII85InputStream: 'z' encoding can only appear at the start of a group, cIndex: "
									+ cIndex);
				}
				b[0] = b[1] = b[2] = b[3] = 0;
				return 4;
			case '~':
				ch = in.read();
				while ((ch >= 0) && (ch != '>') && Character.isWhitespace(ch)) {
					ch = in.read();
				}
				if (ch != '>') {
					throw new EncodingException(
							"ASCII85InputStream: Invalid EOD, expected '>', found "
									+ ch);
				}
				endReached = true;
				break;
			case '\r':
				lineNo++;
				break;
			case '\n':
				if (prev != '\r') {
					lineNo++;
				}
				break;
			case ' ':
			case '\t':
			case '\f':
			case 0:
				// ignored
				break;
			default:
				c[cIndex] = ch;
				cIndex++;
				break;
			}
		}

		if (cIndex > 0) {
			// fill the rest, avoid rounding by padding with "u" characters.
			for (int i = 0; i < c.length; i++) {
				if (i >= cIndex) {
					c[i] = 'u';
				} else {
					c[i] -= '!';
				}
			}

			// convert
			long d = ((c[0] * a85p4) + (c[1] * a85p3) + (c[2] * a85p2)
					+ (c[3] * a85p1) + c[4]) & 0x00000000FFFFFFFFL;

			b[0] = (int) ((d >> 24) & 0x00FF);
			b[1] = (int) ((d >> 16) & 0x00FF);
			b[2] = (int) ((d >> 8) & 0x00FF);
			b[3] = (int) (d & 0x00FF);
		}
		return cIndex - 1;
	}

	/**
	 * Print out ASCII85 of a file
	 * 
	 * @param args
	 *            filename
	 * @throws Exception
	 *             when file does not exist
	 */
	public static void main(String[] args) throws Exception {
		if (args.length < 1) {
			System.err.println("Usage: ASCII85InputStream filename");
			System.exit(1);
		}
		ASCII85InputStream in = new ASCII85InputStream(new FileInputStream(
				args[0]));
		int b = in.read();
		while (b != -1) {
			System.out.write(b);
			b = in.read();
		}
		in.close();
		System.out.flush();
	}
}