DemoFormat.java

/*
  DemoFormat.java

  (c) 2012-2014 Edward Swartz

  All rights reserved. This program and the accompanying materials
  are made available under the terms of the Eclipse Public License v1.0
  which accompanies this distribution, and is available at
  http://www.eclipse.org/legal/epl-v10.html
 */
package v9t9.common.demos;

import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * The demo format is a magic word plus a header, followed by frames.
 * <p/>
 * The header consists of identifying information for the version of V9t9 and
 * the machine demoed, a description and timestamp, a base timing rate, and a
 * table of contents mapping registered buffer identifiers to bytes. Only the
 * tick code (0) is reserved.
 * <p/>
 * The tick code is used to schedule the demo in time. It is followed by a count
 * for the number of ticks represented (which may be zero, but it is expected
 * to be 1 or more). 
 * <p/>
 * Between ticks, frames are represented by zero or more buffers.  Each buffer starts with
 * its code (from the TOC) and a length, and then an array of bytes of that 
 * length.  The interpretation of the contents is up to the registered buffer
 * handler.
 */
public class DemoFormat {
	/** tick byte, followed by byte count, splits frames */
	public static final int TICK = 0;
	
	public static final String VIDEO_REGS = "videoRegs";
	public static final String VIDEO_DATA = "videoData";
	public static final String SOUND_REGS = "soundRegs";
	public static final String SPEECH_DATA = "speechParams";
	public static final String SOUND_DATA = "soundData";

	public static final String V9938_ACCEL = "v9938Accel";
	public static final String PRINTER_DATA = "printerData";

	public static final String PRINTER_NEW_PAGE = "printerNewPage";
	
	/**
	 * Write a variable-length signed integer (UTF-8)
	 */
	public static void writeVariableLengthNumber(OutputStream os, int i) throws IOException {
		if (i < 0) {
			os.write((byte) -1);
			i = -i;
		}

		if (i >= 0 && i < 0x80) {
			// 7 bits
			os.write((byte) i);
		} else if (i >= 0x80 && i < 0x800) {
			// 11 bits
			os.write((byte) (0xc0 | (i >>> 6)));
			os.write((byte) (0x80 | (i & 0x3f)));
		} else if (i >= 0x800 && i < 0x10000) {
			// 16 bits
			os.write((byte) (0xe0 | (i >>> 12)));
			os.write((byte) (0x80 | ((i >>> 6) & 0x3f)));
			os.write((byte) (0x80 | (i & 0x3f)));
		} else if (i >= 0x10000 && i < 0x200000) {
			// 21 bits
			os.write((byte) (0xf0 | (i >>> 18)));
			os.write((byte) (0x80 | ((i >>> 12)) & 0x3f));
			os.write((byte) (0x80 | ((i >>> 6)) & 0x3f));
			os.write((byte) (0x80 | (i & 0x3f)));
		} else if (i >= 0x200000 && i < 0x4000000) {
			// 26 bits
			os.write((byte) (0xf8 | (i >>> 24)));
			os.write((byte) (0x80 | ((i >>> 18)) & 0x3f));
			os.write((byte) (0x80 | ((i >>> 12)) & 0x3f));
			os.write((byte) (0x80 | ((i >>> 6)) & 0x3f));
			os.write((byte) (0x80 | (i & 0x3f)));
		} else {
			// 31 bits
			os.write((byte) (0xfc | (i >>> 30)));
			os.write((byte) (0x80 | ((i >>> 24)) & 0x3f));
			os.write((byte) (0x80 | ((i >>> 18)) & 0x3f));
			os.write((byte) (0x80 | ((i >>> 12)) & 0x3f));
			os.write((byte) (0x80 | ((i >>> 6)) & 0x3f));
			os.write((byte) (0x80 | (i & 0x3f)));
		}
	}
	

	/**
	 * Read a variable-length signed integer (UTF-8)
	 *
	 * @return value
	 * @throws IOException 
	 */
	public static int readVariableLengthNumber(InputStream is) throws IOException {
		boolean neg = false;
		
		int byt = is.read();
		if (byt < 0)
			throw new EOFException();
		if (byt == 0xff) {
			neg = true;
			byt = is.read();
			if (byt < 0)
				throw new EOFException();
		}
		
		int val;
		if (byt < 0x80) {
			// 7 bits
			val = byt;
		}
		else if ((byt & 0xe0) == 0xc0) {
			// 11 bits
			val = ((byt & 0x1f) << 6) 
					| (ensureUtf8(is.read()) << 0);
		}
		else if ((byt & 0xf0) == 0xe0) {
			// 16 bits
			val = ((byt & 0xf) << 12) 
					| (ensureUtf8(is.read()) << 6)
					| (ensureUtf8(is.read()) << 0);
		}
		else if ((byt & 0xf8) == 0xf0) {
			// 21 bits
			val = ((byt & 0x7) << 18) 
					| (ensureUtf8(is.read()) << 12)
					| (ensureUtf8(is.read()) << 6)
					| (ensureUtf8(is.read()) << 0);
		}
		else if ((byt & 0xfc) == 0xf8) {
			// 26 bits
			val = ((byt & 0x3) << 24) 
					| (ensureUtf8(is.read()) << 18)
					| (ensureUtf8(is.read()) << 12)
					| (ensureUtf8(is.read()) << 6)
					| (ensureUtf8(is.read()) << 0);
		}
		else if ((byt & 0xfe) == 0xfc) {
			// 31 bits
			val = ((byt & 0x1) << 30) 
					| (ensureUtf8(is.read()) << 24)
					| (ensureUtf8(is.read()) << 18)
					| (ensureUtf8(is.read()) << 12)
					| (ensureUtf8(is.read()) << 6)
					| (ensureUtf8(is.read()) << 0);
		}
		else {
			throw new IOException("bad numeric encoding (bad leader) 0x" + Integer.toHexString(byt));
		}
		
		return neg ? -val : val;
	}


	private static int ensureUtf8(int read) throws IOException {
		if (read < 0)
			throw new EOFException();
		if ((read & 0xc0) != 0x80)
			throw new IOException("bad numeric encoding (bad trailer) 0x" + Integer.toHexString(read));
		return read & 0x3f;
	}
	


}