first_marker (j_decompress_ptr cinfo)
/* Like next_marker, but used to obtain the initial SOI marker. */
/* For this marker, we do not allow preceding garbage or fill; otherwise,
 * we might well scan an entire input file before realizing it ain't JPEG.
 * If an application wants to process non-JFIF files, it must seek to the
 * SOI before calling the JPEG library.
 */
{
  int c, c2;
  INPUT_VARS(cinfo);

  INPUT_BYTE(cinfo, c, return FALSE);
  INPUT_BYTE(cinfo, c2, return FALSE);
  if (c != 0xFF || c2 != (int) M_SOI)
    ERREXIT2(cinfo, JERR_NO_SOI, c, c2);

  cinfo->unread_marker = c2;

  INPUT_SYNC(cinfo);
  return TRUE;
}


/*
 * Read markers until SOS or EOI.
 *
 * Returns same codes as are defined for jpeg_consume_input:
 * JPEG_SUSPENDED, JPEG_REACHED_SOS, or JPEG_REACHED_EOI.
 */

METHODDEF(int)
read_markers (j_decompress_ptr cinfo)
{
  /* Outer loop repeats once for each marker. */
  for (;;) {
    /* Collect the marker proper, unless we already did. */
    /* NB: first_marker() enforces the requirement that SOI appear first. */
    if (cinfo->unread_marker == 0) {
      if (! cinfo->marker->saw_SOI) {
	if (! first_marker(cinfo))
	  return JPEG_SUSPENDED;
      } else {
	if (! next_marker(cinfo))
	  return JPEG_SUSPENDED;
      }
    }
    /* At this point cinfo->unread_marker contains the marker code and the
     * input point is just past the marker proper, but before any parameters.
     * A suspension will cause us to return with this state still true.
     */
    switch (cinfo->unread_marker) {
    case M_SOI:
      if (! get_soi(cinfo))
	return JPEG_SUSPENDED;
      break;

    case M_SOF0:		/* Baseline */
    case M_SOF1:		/* Extended sequential, Huffman */
      if (! get_sof(cinfo, FALSE, FALSE))
	return JPEG_SUSPENDED;
      break;

    case M_SOF2:		/* Progressive, Huffman */
      if (! get_sof(cinfo, TRUE, FALSE))
	return JPEG_SUSPENDED;
      break;

    case M_SOF9:		/* Extended sequential, arithmetic */
      if (! get_sof(cinfo, FALSE, TRUE))
	return JPEG_SUSPENDED;
      break;

    case M_SOF10:		/* Progressive, arithmetic */
      if (! get_sof(cinfo, TRUE, TRUE))
	return JPEG_SUSPENDED;
      break;

    /* Currently unsupported SOFn types */
    case M_SOF3:		/* Lossless, Huffman */
    case M_SOF5:		/* Differential sequential, Huffman */
    case M_SOF6:		/* Differential progressive, Huffman */
    case M_SOF7:		/* Differential lossless, Huffman */
    case M_JPG:			/* Reserved for JPEG extensions */
    case M_SOF11:		/* Lossless, arithmetic */
    case M_SOF13:		/* Differential sequential, arithmetic */
    case M_SOF14:		/* Differential progressive, arithmetic */
    case M_SOF15:		/* Differential lossless, arithmetic */
      ERREXIT1(cinfo, JERR_SOF_UNSUPPORTED, cinfo->unread_marker);
      break;

    case M_SOS:
      if (! get_sos(cinfo))
	return JPEG_SUSPENDED;
      cinfo->unread_marker = 0;	/* processed the marker */
      return JPEG_REACHED_SOS;
    
    case M_EOI:
      TRACEMS(cinfo, 1, JTRC_EOI);
      cinfo->unread_marker = 0;	/* processed the marker */
      return JPEG_REACHED_EOI;
      
    case M_DAC:
      if (! get_dac(cinfo))
	return JPEG_SUSPENDED;
      break;
      
    case M_DHT:
      if (! get_dht(cinfo))
	return JPEG_SUSPENDED;
      break;
      
    case M_DQT:
      if (! get_dqt(cinfo))
	return JPEG_SUSPENDED;
      break;
      
    case M_DRI:
      if (! get_dri(cinfo))
	return JPEG_SUSPENDED;
      break;
      
    case M_APP0:
    case M_APP1:
    case M_APP2:
    case M_APP3:
    case M_APP4:
    case M_APP5:
    case M_APP6:
    case M_APP7:
    case M_APP8:
    case M_APP9:
    case M_APP10:
    case M_APP11:
    case M_APP12:
    case M_APP13:
    case M_APP14:
    case M_APP15:
      if (! (*cinfo->marker->process_APPn[cinfo->unread_marker - (int) M_APP0]) (cinfo))
	return JPEG_SUSPENDED;
      break;
      
    case M_COM:
      if (! (*cinfo->marker->process_COM) (cinfo))
	return JPEG_SUSPENDED;
      break;

    case M_RST0:		/* these are all parameterless */
    case M_RST1:
    case M_RST2:
    case M_RST3:
    case M_RST4:
    case M_RST5:
    case M_RST6:
    case M_RST7:
    case M_TEM:
      TRACEMS1(cinfo, 1, JTRC_PARMLESS_MARKER, cinfo->unread_marker);
      break;

    case M_DNL:			/* Ignore DNL ... perhaps the wrong thing */
      if (! skip_variable(cinfo))
	return JPEG_SUSPENDED;
      break;

    default:			/* must be DHP, EXP, JPGn, or RESn */
      /* For now, we treat the reserved markers as fatal errors since they are
       * likely to be used to signal incompatible JPEG Part 3 extensions.
       * Once the JPEG 3 version-number marker is well defined, this code
       * ought to change!
       */
      ERREXIT1(cinfo, JERR_UNKNOWN_MARKER, cinfo->unread_marker);
      break;
    }
    /* Successfully processed marker, so reset state variable */
    cinfo->unread_marker = 0;
  } /* end loop */
}


/*
 * Read a restart marker, which is expected to appear next in the datastream;
 * if the marker is not there, take appropriate recovery action.
 * Returns FALSE if suspension is required.
 *
 * This is called by the entropy decoder after it has read an appropriate
 * number of MCUs.  cinfo->unread_marker may be nonzero if the entropy decoder
 * has already read a marker from the data source.  Under normal conditions
 * cinfo->unread_marker will be reset to 0 before returning; if not reset,
 * it holds a marker which the decoder will be unable to read past.
 */

METHODDEF(boolean)
read_restart_marker (j_decompress_ptr cinfo)
{
  /* Obtain a marker unless we already did. */
  /* Note that next_marker will complain if it skips any data. */
  if (cinfo->unread_marker == 0) {
    if (! next_marker(cinfo))
      return FALSE;
  }

  if (cinfo->unread_marker ==
      ((int) M_RST0 + cinfo->marker->next_restart_num)) {
    /* Normal case --- swallow the marker and let entropy decoder continue */
    TRACEMS1(cinfo, 3, JTRC_RST, cinfo->marker->next_restart_num);
    cinfo->unread_marker = 0;
  } else {
    /* Uh-oh, the restart markers have been messed up. */
    /* Let the data source manager determine how to resync. */
    if (! (*cinfo->src->resync_to_restart) (cinfo,
					    cinfo->marker->next_restart_num))
      return FALSE;
  }

  /* Update next-restart state */
  cinfo->marker->next_restart_num = (cinfo->marker->next_restart_num + 1) & 7;

  return TRUE;
}


/*
 * This is the default resync_to_restart method for data source managers
 * to use if they don't have any better approach.  Some data source managers
 * may be able to back up, or may have additional knowledge about the data
 * which permits a more intelligent recovery strategy; such managers would
 * presumably supply their own resync method.
 *
 * read_restart_marker calls resync_to_restart if it finds a marker other than
 * the restart marker it was expecting.  (This code is *not* used unless
 * a nonzero restart interval has been declared.)  cinfo->unread_marker is
 * the marker code actually found (might be anything, except 0 or FF).
 * The desired restart marker number (0..7) is passed as a parameter.
 * This routine is supposed to apply whatever error recovery strategy seems
 * appropriate in order to position the input stream to the next data segment.
 * Note that cinfo->unread_marker is treated as a marker appearing before
 * the current data-source input point; usually it should be reset to zero
 * before returning.
 * Returns FALSE if suspension is required.
 *
 * This implementation is substantially constrained by wanting to treat the
 * input as a data stream; this means we can't back up.  Therefore, we have
 * only the following actions to work with:
 *   1. Simply discard the marker and let the entropy decoder resume at next
 *      byte of file.
 *   2. Read forward until we find another marker, discarding intervening
 *      data.  (In theory we could look ahead within the current bufferload,
 *      without having to discard data if we don't find the desired marker.
 *      This idea is not implemented here, in part because it makes behavior
 *      dependent on buffer size and chance buffer-boundary positions.)
 *   3. Leave the marker unread (by failing to zero cinfo->unread_marker).
 *      This will cause the entropy decoder to process an empty data segment,
 *      inserting dummy zeroes, and then we will reprocess the marker.
 *
 * #2 is appropriate if we think the desired marker lies ahead, while #3 is
 * appropriate if the found marker is a future restart marker (indicating
 * that we have missed the desired restart marker, probably because it got
 * corrupted).
 * We apply #2 or #3 if the found marker is a restart marker no more than
 * two counts behind or ahead of the expected one.  We also apply #2 if the
 * found marker is not a legal JPEG marker code (it's certainly bogus data).
 * If the found marker is a restart marker more than 2 counts away, we do #1
 * (too much risk that the marker is erroneous; with luck we will be able to
 * resync at some future point).
 * For any valid non-restart JPEG marker, we apply #3.  This keeps us from
 * overrunning the end of a scan.  An implementation limited to single-scan
 * files might find it better to apply #2 for markers other than EOI, since
 * any other marker would have to be bogus data in that case.
 */

GLOBAL(boolean)
jpeg_resync_to_restart (j_decompress_ptr cinfo, int desired)
{
  int marker = cinfo->unread_marker;
  int action = 1;
  
  /* Always put up a warning. */
  WARNMS2(cinfo, JWRN_MUST_RESYNC, marker, desired);
  
  /* Outer loop handles repeated decision after scanning forward. */
  for (;;) {
    if (marker < (int) M_SOF0)
      action = 2;		/* invalid marker */
    else if (marker < (int) M_RST0 || marker > (int) M_RST7)
      action = 3;		/* valid non-restart marker */
    else {
      if (marker == ((int) M_RST0 + ((desired+1) & 7)) ||
	  marker == ((int) M_RST0 + ((desired+2) & 7)))
	action = 3;		/* one of the next two expected restarts */
      else if (marker == ((int) M_RST0 + ((desired-1) & 7)) ||
	       marker == ((int) M_RST0 + ((desired-2) & 7)))
	action = 2;		/* a prior restart, so advance */
      else
	action = 1;		/* desired restart or too far away */
    }
    TRACEMS2(cinfo, 4, JTRC_RECOVERY_ACTION, marker, action);
    switch (action) {
    case 1:
      /* Discard marker and let entropy decoder resume processing. */
      cinfo->unread_marker = 0;
      return TRUE;
    case 2:
      /* Scan to the next marker, and repeat the decision loop. */
      if (! next_marker(cinfo))
	return FALSE;
      marker = cinfo->unread_marker;
      break;
    case 3:
      /* Return without advancing past this marker. */
      /* Entropy decoder will be forced to process an empty segment. */
      return TRUE;
    }
  } /* end loop */
}


/*
 * Reset marker processing state to begin a fresh datastream.
 */

METHODDEF(void)
reset_marker_reader (j_decompress_ptr cinfo)
{
  cinfo->comp_info = NULL;		/* until allocated by get_sof */
  cinfo->input_scan_number = 0;		/* no SOS seen yet */
  cinfo->unread_marker = 0;		/* no pending marker */
  cinfo->marker->saw_SOI = FALSE;	/* set internal state too */
  cinfo->marker->saw_SOF = FALSE;
  cinfo->marker->discarded_bytes = 0;
}


/*
 * Initialize the marker reader module.
 * This is called only once, when the decompression object is created.
 */

GLOBAL(void)
jinit_marker_reader (j_decompress_ptr cinfo)
{
  int i;

  /* Create subobject in permanent pool */
  cinfo->marker = (struct jpeg_marker_reader *)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
				SIZEOF(struct jpeg_marker_reader));
  /* Initialize method pointers */
  cinfo->marker->reset_marker_reader = reset_marker_reader;
  cinfo->marker->read_markers = read_markers;
  cinfo->marker->read_restart_marker = read_restart_marker;
  cinfo->marker->process_COM = skip_variable;
  for (i = 0; i < 16; i++)
    cinfo->marker->process_APPn[i] = skip_variable;
  cinfo->marker->process_APPn[0] = get_app0;
  cinfo->marker->process_APPn[14] = get_app14;
  /* Reset marker processing state */
  reset_marker_reader(cinfo);
}