gt:     return read() | (read() << 8);
context: package gif;
  
  import java.net.*;
  import java.io.*;
  import java.util.*;
  import java.awt.*;
  import java.awt.image.*;
  
  /**
   * Class GifDecoder - Decodes a GIF file into one or more frames.
   * <br><pre>
   * Example:
   *    GifDecoder d = new GifDecoder();
   *    d.read("sample.gif");
   *    int n = d.getFrameCount();
   *    for (int i = 0; i < n; i++) {
   *       BufferedImage frame = d.getFrame(i);  // frame i
   *       int t = d.getDelay(i);  // display duration of frame in milliseconds
   *       // do something with frame
   *    }
   * </pre>
   * No copyright asserted on the source code of this class.  May be used for
   * any purpose, however, refer to the Unisys LZW patent for any additional
   * restrictions.  Please forward any corrections to kweiner@fmsware.com.
   *
   * @author Kevin Weiner, FM Software; LZW decoder adapted from John Cristy's ImageMagick.
   * @version 1.03 November 2003
   *
   */
  
  public class GifDecoder {
  
    /**
     * File read status: No errors.
     */
    public static final int STATUS_OK = 0;
  
    /**
     * File read status: Error decoding file (may be partially decoded)
     */
    public static final int STATUS_FORMAT_ERROR = 1;
  
    /**
     * File read status: Unable to open source.
     */
    public static final int STATUS_OPEN_ERROR = 2;
  
    protected BufferedInputStream in;
    protected int status;
  
    protected int width; // full image width
    protected int height; // full image height
    protected boolean gctFlag; // global color table used
    protected int gctSize; // size of global color table
    protected int loopCount = 1; // iterations; 0 = repeat forever
  
    protected int[] gct; // global color table
    protected int[] lct; // local color table
    protected int[] act; // active color table
  
    protected int bgIndex; // background color index
    protected int bgColor; // background color
    protected int lastBgColor; // previous bg color
    protected int pixelAspect; // pixel aspect ratio
  
    protected boolean lctFlag; // local color table flag
    protected boolean interlace; // interlace flag
    protected int lctSize; // local color table size
  
    protected int ix, iy, iw, ih; // current image rectangle
    protected Rectangle lastRect; // last image rect
    protected BufferedImage image; // current frame
    protected BufferedImage lastImage; // previous frame
  
    protected byte[] block = new byte[256]; // current data block
    protected int blockSize = 0; // block size
  
    // last graphic control extension info
    protected int dispose = 0;
    // 0=no action; 1=leave in place; 2=restore to bg; 3=restore to prev
    protected int lastDispose = 0;
    protected boolean transparency = false; // use transparent color
    protected int delay = 0; // delay in milliseconds
    protected int transIndex; // transparent color index
  
    protected static final int MaxStackSize = 4096;
    // max decoder pixel stack size
  
    // LZW decoder working arrays
    protected short[] prefix;
    protected byte[] suffix;
    protected byte[] pixelStack;
    protected byte[] pixels;
  
    protected ArrayList frames; // frames read from current file
    protected int frameCount;
  
    static class GifFrame {
      public GifFrame(BufferedImage im, int del) {
        image = im;
        delay = del;
      }
      public BufferedImage image;
      public int delay;
    }
  
    /**
     * Gets display duration for specified frame.
     *
     * @param n int index of frame
     * @return delay in milliseconds
     */
    public int getDelay(int n) {
      //
      delay = -1;
      if ((n >= 0) && (n < frameCount)) {
        delay = ((GifFrame) frames.get(n)).delay;
      }
      return delay;
    }
  
    /**
     * Gets the number of frames read from file.
     * @return frame count
     */
    public int getFrameCount() {
      return frameCount;
    }
  
    /**
     * Gets the first (or only) image read.
     *
     * @return BufferedImage containing first frame, or null if none.
     */
    public BufferedImage getImage() {
      return getFrame(0);
    }
  
    /**
     * Gets the "Netscape" iteration count, if any.
     * A count of 0 means repeat indefinitiely.
     *
     * @return iteration count if one was specified, else 1.
     */
    public int getLoopCount() {
      return loopCount;
    }
  
    /**
     * Creates new frame image from current data (and previous
     * frames as specified by their disposition codes).
     */
    protected void setPixels() {
      // expose destination image's pixels as int array
      int[] dest =
        ((DataBufferInt) image.getRaster().getDataBuffer()).getData();
  
      // fill in starting image contents based on last image's dispose code
      if (lastDispose > 0) {
        if (lastDispose == 3) {
          // use image before last
          int n = frameCount - 2;
          if (n > 0) {
            lastImage = getFrame(n - 1);
          } else {
            lastImage = null;
          }
        }
  
        if (lastImage != null) {
          int[] prev =
            ((DataBufferInt) lastImage.getRaster().getDataBuffer()).getData();
          System.arraycopy(prev, 0, dest, 0, width * height);
          // copy pixels
  
          if (lastDispose == 2) {
            // fill last image rect area with background color
            Graphics2D g = image.createGraphics();
            Color c = null;
            if (transparency) {
              c = new Color(0, 0, 0, 0);  // assume background is transparent
            } else {
              c = new Color(lastBgColor); // use given background color
            }
            g.setColor(c);
            g.setComposite(AlphaComposite.Src); // replace area
            g.fill(lastRect);
            g.dispose();
          }
        }
      }
  
      // copy each source line to the appropriate place in the destination
      int pass = 1;
      int inc = 8;
      int iline = 0;
      for (int i = 0; i < ih; i++) {
        int line = i;
        if (interlace) {
          if (iline >= ih) {
            pass++;
            switch (pass) {
              case 2 :
                iline = 4;
                break;
              case 3 :
                iline = 2;
                inc = 4;
                break;
              case 4 :
                iline = 1;
                inc = 2;
            }
          }
          line = iline;
          iline += inc;
        }
        line += iy;
        if (line < height) {
          int k = line * width;
          int dx = k + ix; // start of line in dest
          int dlim = dx + iw; // end of dest line
          if ((k + width) < dlim) {
            dlim = k + width; // past dest edge
          }
          int sx = i * iw; // start of line in source
          while (dx < dlim) {
            // map color and insert in destination
            int index = ((int) pixels[sx++]) & 0xff;
            int c = act[index];
            if (c != 0) {
              dest[dx] = c;
            }
            dx++;
          }
        }
      }
    }
  
    /**
     * Gets the image contents of frame n.
     *
     * @return BufferedImage representation of frame, or null if n is invalid.
     */
    public BufferedImage getFrame(int n) {
      BufferedImage im = null;
      if ((n >= 0) && (n < frameCount)) {
        im = ((GifFrame) frames.get(n)).image;
      }
      return im;
    }
  
    /**
     * Gets image size.
     *
     * @return GIF image dimensions
     */
    public Dimension getFrameSize() {
      return new Dimension(width, height);
    }
  
    /**
     * Reads GIF image from stream
     *
     * @param BufferedInputStream containing GIF file.
     * @return read status code (0 = no errors)
     */
    public int read(BufferedInputStream is) {
      init();
      if (is != null) {
        in = is;
        readHeader();
        if (!err()) {
          readContents();
          if (frameCount < 0) {
            status = STATUS_FORMAT_ERROR;
          }
        }
      } else {
        status = STATUS_OPEN_ERROR;
      }
      try {
        is.close();
      } catch (IOException e) {
      }
      return status;
    }
  
    /**
     * Reads GIF image from stream
     *
     * @param InputStream containing GIF file.
     * @return read status code (0 = no errors)
     */
    public int read(InputStream is) {
      init();
      if (is != null) {
        if (!(is instanceof BufferedInputStream))
          is = new BufferedInputStream(is);
        in = (BufferedInputStream) is;
        readHeader();
        if (!err()) {
          readContents();
          if (frameCount < 0) {
            status = STATUS_FORMAT_ERROR;
          }
        }
      } else {
        status = STATUS_OPEN_ERROR;
      }
      try {
        is.close();
      } catch (IOException e) {
      }
      return status;
    }
  
    /**
     * Reads GIF file from specified file/URL source  
     * (URL assumed if name contains ":/" or "file:")
     *
     * @param name String containing source
     * @return read status code (0 = no errors)
     */
    public int read(String name) {
      status = STATUS_OK;
      try {
        name = name.trim().toLowerCase();
        if ((name.indexOf("file:") >= 0) ||
          (name.indexOf(":/") > 0)) {
          URL url = new URL(name);
          in = new BufferedInputStream(url.openStream());
        } else {
          in = new BufferedInputStream(new FileInputStream(name));
        }
        status = read(in);
      } catch (IOException e) {
        status = STATUS_OPEN_ERROR;
      }
  
      return status;
    }
  
    /**
     * Decodes LZW image data into pixel array.
     * Adapted from John Cristy's ImageMagick.
     */
    protected void decodeImageData() {
      int NullCode = -1;
      int npix = iw * ih;
      int available, 
        clear,
        code_mask,
        code_size,
        end_of_information,
        in_code,
        old_code,
        bits,
        code,
        count,
        i,
        datum,
        data_size,
        first,
        top,
        bi,
        pi;
  
      if ((pixels == null) || (pixels.length < npix)) {
        pixels = new byte[npix]; // allocate new pixel array
      }
      if (prefix == null) prefix = new short[MaxStackSize];
      if (suffix == null) suffix = new byte[MaxStackSize];
      if (pixelStack == null) pixelStack = new byte[MaxStackSize + 1];
  
      //  Initialize GIF data stream decoder.
  
      data_size = read();
      clear = 1 << data_size;
      end_of_information = clear + 1;
      available = clear + 2;
      old_code = NullCode;
      code_size = data_size + 1;
      code_mask = (1 << code_size) - 1;
      for (code = 0; code < clear; code++) {
        prefix[code] = 0;
        suffix[code] = (byte) code;
      }
  
      //  Decode GIF pixel stream.
  
      datum = bits = count = first = top = pi = bi = 0;
  
      for (i = 0; i < npix;) {
        if (top == 0) {
          if (bits < code_size) {
            //  Load bytes until there are enough bits for a code.
            if (count == 0) {
              // Read a new data block.
              count = readBlock();
              if (count <= 0)
                break;
              bi = 0;
            }
            datum += (((int) block[bi]) & 0xff) << bits;
            bits += 8;
            bi++;
            count--;
            continue;
          }
  
          //  Get the next code.
  
          code = datum & code_mask;
          datum >>= code_size;
          bits -= code_size;
  
          //  Interpret the code
  
          if ((code > available) || (code == end_of_information))
            break;
          if (code == clear) {
            //  Reset decoder.
            code_size = data_size + 1;
            code_mask = (1 << code_size) - 1;
            available = clear + 2;
            old_code = NullCode;
            continue;
          }
          if (old_code == NullCode) {
            pixelStack[top++] = suffix[code];
            old_code = code;
            first = code;
            continue;
          }
          in_code = code;
          if (code == available) {
            pixelStack[top++] = (byte) first;
            code = old_code;
          }
          while (code > clear) {
            pixelStack[top++] = suffix[code];
            code = prefix[code];
          }
          first = ((int) suffix[code]) & 0xff;
  
          //  Add a new string to the string table,
  
          if (available >= MaxStackSize)
            break;
          pixelStack[top++] = (byte) first;
          prefix[available] = (short) old_code;
          suffix[available] = (byte) first;
          available++;
          if (((available & code_mask) == 0)
            && (available < MaxStackSize)) {
            code_size++;
            code_mask += available;
          }
          old_code = in_code;
        }
  
        //  Pop a pixel off the pixel stack.
  
        top--;
        pixels[pi++] = pixelStack[top];
        i++;
      }
  
      for (i = pi; i < npix; i++) {
        pixels[i] = 0; // clear missing pixels
      }
  
    }
  
    /**
     * Returns true if an error was encountered during reading/decoding
     */
    protected boolean err() {
      return status != STATUS_OK;
    }
  
    /**
     * Initializes or re-initializes reader
     */
    protected void init() {
      status = STATUS_OK;
      frameCount = 0;
      frames = new ArrayList();
      gct = null;
      lct = null;
    }
  
    /**
     * Reads a single byte from the input stream.
     */
    protected int read() {
      int curByte = 0;
      try {
        curByte = in.read();
      } catch (IOException e) {
        status = STATUS_FORMAT_ERROR;
      }
      return curByte;
    }
  
    /**
     * Reads next variable length block from input.
     *
     * @return number of bytes stored in "buffer"
     */
    protected int readBlock() {
      blockSize = read();
      int n = 0;
      if (blockSize > 0) {
        try {
          int count = 0;
          while (n < blockSize) {
            count = in.read(block, n, blockSize - n);
            if (count == -1) 
              break;
            n += count;
          }
        } catch (IOException e) {
        }
  
        if (n < blockSize) {
          status = STATUS_FORMAT_ERROR;
        }
      }
      return n;
    }
  
    /**
     * Reads color table as 256 RGB integer values
     *
     * @param ncolors int number of colors to read
     * @return int array containing 256 colors (packed ARGB with full alpha)
     */
    protected int[] readColorTable(int ncolors) {
      int nbytes = 3 * ncolors;
      int[] tab = null;
      byte[] c = new byte[nbytes];
      int n = 0;
      try {
        n = in.read(c);
      } catch (IOException e) {
      }
      if (n < nbytes) {
        status = STATUS_FORMAT_ERROR;
      } else {
        tab = new int[256]; // max size to avoid bounds checks
        int i = 0;
        int j = 0;
        while (i < ncolors) {
          int r = ((int) c[j++]) & 0xff;
          int g = ((int) c[j++]) & 0xff;
          int b = ((int) c[j++]) & 0xff;
          tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
        }
      }
      return tab;
    }
  
    /**
     * Main file parser.  Reads GIF content blocks.
     */
    protected void readContents() {
      // read GIF file content blocks
      boolean done = false;
      while (!(done || err())) {
        int code = read();
        switch (code) {
  
          case 0x2C : // image separator
            readImage();
            break;
  
          case 0x21 : // extension
            code = read();
            switch (code) {
              case 0xf9 : // graphics control extension
                readGraphicControlExt();
                break;
  
              case 0xff : // application extension
                readBlock();
                String app = "";
                for (int i = 0; i < 11; i++) {
                  app += (char) block[i];
                }
                if (app.equals("NETSCAPE2.0")) {
                  readNetscapeExt();
                }
                else
                  skip(); // don't care
                break;
  
              default : // uninteresting extension
                skip();
            }
            break;
  
          case 0x3b : // terminator
            done = true;
            break;
  
          case 0x00 : // bad byte, but keep going and see what happens
            break;
  
          default :
            status = STATUS_FORMAT_ERROR;
        }
      }
    }
  
    /**
     * Reads Graphics Control Extension values
     */
    protected void readGraphicControlExt() {
      read(); // block size
      int packed = read(); // packed fields
      dispose = (packed & 0x1c) >> 2; // disposal method
      if (dispose == 0) {
        dispose = 1; // elect to keep old image if discretionary
      }
      transparency = (packed & 1) != 0;
      delay = readShort() * 10; // delay in milliseconds
      transIndex = read(); // transparent color index
      read(); // block terminator
    }
  
    /**
     * Reads GIF file header information.
     */
    protected void readHeader() {
      String id = "";
      for (int i = 0; i < 6; i++) {
        id += (char) read();
      }
      if (!id.startsWith("GIF")) {
        status = STATUS_FORMAT_ERROR;
        return;
      }
  
      readLSD();
      if (gctFlag && !err()) {
        gct = readColorTable(gctSize);
        bgColor = gct[bgIndex];
      }
    }
  
    /**
     * Reads next frame image
     */
    protected void readImage() {
      ix = readShort(); // (sub)image position & size
      iy = readShort();
      iw = readShort();
      ih = readShort();
  
      int packed = read();
      lctFlag = (packed & 0x80) != 0; // 1 - local color table flag
      interlace = (packed & 0x40) != 0; // 2 - interlace flag
      // 3 - sort flag
      // 4-5 - reserved
      lctSize = 2 << (packed & 7); // 6-8 - local color table size
  
      if (lctFlag) {
        lct = readColorTable(lctSize); // read table
        act = lct; // make local table active
      } else {
        act = gct; // make global table active
        if (bgIndex == transIndex)
          bgColor = 0;
      }
      int save = 0;
      if (transparency) {
        save = act[transIndex];
        act[transIndex] = 0; // set transparent color if specified
      }
  
      if (act == null) {
        status = STATUS_FORMAT_ERROR; // no color table defined
      }
  
      if (err()) return;
  
      decodeImageData(); // decode pixel data
      skip();
  
      if (err()) return;
  
      frameCount++;
  
      // create new image to receive frame data
      image =
        new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB_PRE);
  
      setPixels(); // transfer pixel data to image
  
      frames.add(new GifFrame(image, delay)); // add image to frame list
  
      if (transparency) {
        act[transIndex] = save;
      }
      resetFrame();
  
    }
  
    /**
     * Reads Logical Screen Descriptor
     */
    protected void readLSD() {
  
      // logical screen size
      width = readShort();
      height = readShort();
  
      // packed fields
      int packed = read();
      gctFlag = (packed & 0x80) != 0; // 1   : global color table flag
      // 2-4 : color resolution
      // 5   : gct sort flag
      gctSize = 2 << (packed & 7); // 6-8 : gct size
  
      bgIndex = read(); // background color index
      pixelAspect = read(); // pixel aspect ratio
    }
  
    /**
     * Reads Netscape extenstion to obtain iteration count
     */
    protected void readNetscapeExt() {
      do {
        readBlock();
        if (block[0] == 1) {
          // loop count sub-block
          int b1 = ((int) block[1]) & 0xff;
          int b2 = ((int) block[2]) & 0xff;
          loopCount = (b2 << 8) | b1;
        }
      } while ((blockSize > 0) && !err());
    }
  
    /**
     * Reads next 16-bit value, LSB first
     */
    protected int readShort() {
      // read 16-bit value, LSB first
  