gcc/libjava/classpath/gnu/javax/imageio/jpeg/JPEGImageInputStream.java

/* JPEGImageInputStream.java --
   Copyright (C)  2006  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath 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
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package gnu.javax.imageio.jpeg;

import java.io.IOException;
import javax.imageio.stream.ImageInputStream;
import javax.imageio.stream.ImageInputStreamImpl;

public class JPEGImageInputStream
  extends ImageInputStreamImpl
{
  private ImageInputStream in;

  byte marker;

  public JPEGImageInputStream(ImageInputStream in)
  {
    super();

    this.in = in;
  }

  public int read()
    throws IOException
  {
    setBitOffset(0);
    return in.read();
  }

  public int read(byte[] data, int offset, int len)
    throws IOException
  {
    setBitOffset(0);
    return in.read(data, offset, len);
  }

  /**
   * Pull a byte from the stream, this checks to see if the byte is 0xff
   * and if the next byte isn't 0x00 (stuffed byte) it errors out. If it's
   * 0x00 then it simply ignores the byte.
   *
   * @return the next byte in the buffer
   *
   * @throws IOException TODO
   * @throws BitStreamException TODO
   */
  private byte pullByte() throws IOException, JPEGMarkerFoundException
  {
    byte mybyte = readByte();
    // FIXME: handle multiple 0xff in a row
    if(mybyte==(byte)(0xff))
      {
        byte secondbyte = readByte();
        if(secondbyte != (byte)(0x00))
          {
            marker = secondbyte;
            throw new JPEGMarkerFoundException();
          }
      }
    return mybyte;
  }

  /**
   * This returns the marker that was last encountered.  This should only be
   * used if removeBit() throws a MarkerTagFound exception.
   *
   * @return marker as byte
   */
  public byte getMarker()
  {
    return marker;
  }

  /**
   * Removes a bit from the buffer. (Removes from the top of a queue). This
   * also checks for markers and throws MarkerTagFound exception if it does.
   * If MarkerTagFound is thrown you can use getMarker() method to get the
   * marker that caused the throw.
   *
   * @param l specifies how many bits you want to remove and add to the
   *        integer
   * @return the amount of bits specified by l as an integer
   *
   * @throws IOException TODO
   * @throws JPEGMarkerFoundException
   * @throws BitStreamException TODO
   */
  public int readBit()
  throws IOException, JPEGMarkerFoundException
{
  checkClosed();

  // Calc new bit offset here, readByte resets it.
  int newOffset = (bitOffset + 1) & 0x7;

  byte data = pullByte();

  if (bitOffset != 0)
    {
        seek(getStreamPosition() - 1);
        data = (byte) (data >> (8 - newOffset));
    }

  bitOffset = newOffset;
  return data & 0x1;
}


  /**
   * This method skips over the the data and finds the next position
   * in the bit sequence with a X'FF' X'??' sequence.  Multiple X'FF
   * bytes in sequence are considered padding and interpreted as one
   * X'FF byte.
   *
   * @return the next marker byte in the stream
   * @throws IOException if the end of the stream is reached
   * unexpectedly
   */
  public byte findNextMarker()
    throws IOException
  {
    boolean marked0xff = false;
    byte byteinfo = JPEGMarker.X00;

    setBitOffset(0);
    while (true)
      {
        byteinfo = readByte();
        if (!marked0xff)
          {
            if (byteinfo == JPEGMarker.XFF)
              marked0xff = true;
          }
        else
          {
            if (byteinfo == JPEGMarker.XFF)
              // Ignore the value 0xff when it is immediately
              // followed by another 0xff byte.
              continue;
            else if (byteinfo == JPEGMarker.X00)
              // The sequence 0xff 0x00 is used to encode the
              // actual value 0xff.  So restart our search for a
              // marker.
              marked0xff = false;
            else
              // One or more 0xff values were follwed by a
              // non-0x00, non-0xff value so return this as the
              // marker byte.
              return byteinfo;
          }
      }
  }
}