PushBackStream.java

/***************************************************************************
 *  JLayerME is a JAVA library that decodes/plays/converts MPEG 1/2 Layer 3.
 *  Project Homepage: http://www.javazoom.net/javalayer/javalayerme.html.
 *  Copyright (C) JavaZOOM 1999-2005.
 *
 *  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *---------------------------------------------------------------------------
 */
package javazoom.jlme.decoder;

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

public class PushBackStream {
	private byte[] buf;

	private int pos, temp, temp2, avail;

	private InputStream in;

	public PushBackStream(InputStream in, int size) {
		this.in = in;
		this.buf = new byte[size];
		this.pos = size;
	}

	public int read(byte[] b, int off, int len) throws IOException {
		avail = buf.length - pos;
		if (avail > 0) {
			if (len < avail)
				avail = len;

			if (avail == 3) {
				temp = pos;
				temp2 = off;
				b[temp2++] = buf[temp++];
				b[temp2++] = buf[temp++];
				b[temp2] = buf[temp];
			} else { // equals 1
				b[off] = buf[pos];
			}

			pos += avail;
			off += avail;
			len -= avail;
		}

		if (len > 0) {
			if ((len = in.read(b, off, len)) == -1)
				return avail == 0 ? -1 : avail;

			return avail + len;
		}

		return avail;
	}

	public void unread(byte[] b, int off, int len) {
		temp = pos -= 4;

		buf[temp++] = b[off++];
		buf[temp++] = b[off++];
		buf[temp++] = b[off++];
		buf[temp] = b[off++];
	}

	public synchronized void close() throws IOException {
		if (in == null)
			return;
		in.close();
		in = null;
		buf = null;
	}

}