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

   1 /* JPEGImageInputStream.java --
   2    Copyright (C)  2006  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package gnu.javax.imageio.jpeg;
  39
  40 import java.io.IOException;
  41 import javax.imageio.stream.ImageInputStream;
  42 import javax.imageio.stream.ImageInputStreamImpl;
  43
  44 public class JPEGImageInputStream
  45   extends ImageInputStreamImpl
  46 {
  47   private ImageInputStream in;
  48
  49   byte marker;
  50
  51   public JPEGImageInputStream(ImageInputStream in)
  52   {
  53     super();
  54
  55     this.in = in;
  56   }
  57
  58   public int read()
  59     throws IOException
  60   {
  61     setBitOffset(0);
  62     return in.read();
  63   }
  64
  65   public int read(byte[] data, int offset, int len)
  66     throws IOException
  67   {
  68     setBitOffset(0);
  69     return in.read(data, offset, len);
  70   }
  71
  72   /**
  73    * Pull a byte from the stream, this checks to see if the byte is 0xff
  74    * and if the next byte isn't 0x00 (stuffed byte) it errors out. If it's
  75    * 0x00 then it simply ignores the byte.
  76    *
  77    * @return the next byte in the buffer
  78    *
  79    * @throws IOException TODO
  80    * @throws BitStreamException TODO
  81    */
  82   private byte pullByte() throws IOException, JPEGMarkerFoundException
  83   {
  84     byte mybyte = readByte();
  85     // FIXME: handle multiple 0xff in a row
  86     if(mybyte==(byte)(0xff))
  87       {
  88         byte secondbyte = readByte();
  89         if(secondbyte != (byte)(0x00))
  90           {
  91             marker = secondbyte;
  92             throw new JPEGMarkerFoundException();
  93           }
  94       }
  95     return mybyte;
  96   }
  97
  98   /**
  99    * This returns the marker that was last encountered.  This should only be
 100    * used if removeBit() throws a MarkerTagFound exception.
 101    *
 102    * @return marker as byte
 103    */
 104   public byte getMarker()
 105   {
 106     return marker;
 107   }
 108
 109   /**
 110    * Removes a bit from the buffer. (Removes from the top of a queue). This
 111    * also checks for markers and throws MarkerTagFound exception if it does.
 112    * If MarkerTagFound is thrown you can use getMarker() method to get the
 113    * marker that caused the throw.
 114    *
 115    * @param l specifies how many bits you want to remove and add to the
 116    *        integer
 117    * @return the amount of bits specified by l as an integer
 118    *
 119    * @throws IOException TODO
 120    * @throws JPEGMarkerFoundException
 121    * @throws BitStreamException TODO
 122    */
 123   public int readBit()
 124   throws IOException, JPEGMarkerFoundException
 125 {
 126   checkClosed();
 127
 128   // Calc new bit offset here, readByte resets it.
 129   int newOffset = (bitOffset + 1) & 0x7;
 130
 131   byte data = pullByte();
 132
 133   if (bitOffset != 0)
 134     {
 135         seek(getStreamPosition() - 1);
 136         data = (byte) (data >> (8 - newOffset));
 137     }
 138
 139   bitOffset = newOffset;
 140   return data & 0x1;
 141 }
 142
 143
 144   /**
 145    * This method skips over the the data and finds the next position
 146    * in the bit sequence with a X'FF' X'??' sequence.  Multiple X'FF
 147    * bytes in sequence are considered padding and interpreted as one
 148    * X'FF byte.
 149    *
 150    * @return the next marker byte in the stream
 151    * @throws IOException if the end of the stream is reached
 152    * unexpectedly
 153    */
 154   public byte findNextMarker()
 155     throws IOException
 156   {
 157     boolean marked0xff = false;
 158     byte byteinfo = JPEGMarker.X00;
 159
 160     setBitOffset(0);
 161     while (true)
 162       {
 163         byteinfo = readByte();
 164         if (!marked0xff)
 165           {
 166             if (byteinfo == JPEGMarker.XFF)
 167               marked0xff = true;
 168           }
 169         else
 170           {
 171             if (byteinfo == JPEGMarker.XFF)
 172               // Ignore the value 0xff when it is immediately
 173               // followed by another 0xff byte.
 174               continue;
 175             else if (byteinfo == JPEGMarker.X00)
 176               // The sequence 0xff 0x00 is used to encode the
 177               // actual value 0xff.  So restart our search for a
 178               // marker.
 179               marked0xff = false;
 180             else
 181               // One or more 0xff values were follwed by a
 182               // non-0x00, non-0xff value so return this as the
 183               // marker byte.
 184               return byteinfo;
 185           }
 186       }
 187   }
 188 }