if (cinfo->Ah != 0 && !cinfo->arith_code)
	  td = 0;		/* no DC table either */
      } else {
	td = 0;			/* AC scan */
      }
    }
    emit_byte(cinfo, (td << 4) + ta);
  }

  emit_byte(cinfo, cinfo->Ss);
  emit_byte(cinfo, cinfo->Se);
  emit_byte(cinfo, (cinfo->Ah << 4) + cinfo->Al);
}


LOCAL(void)
emit_jfif_app0 (j_compress_ptr cinfo)
/* Emit a JFIF-compliant APP0 marker */
{
  /*
   * Length of APP0 block	(2 bytes)
   * Block ID			(4 bytes - ASCII "JFIF")
   * Zero byte			(1 byte to terminate the ID string)
   * Version Major, Minor	(2 bytes - 0x01, 0x01)
   * Units			(1 byte - 0x00 = none, 0x01 = inch, 0x02 = cm)
   * Xdpu			(2 bytes - dots per unit horizontal)
   * Ydpu			(2 bytes - dots per unit vertical)
   * Thumbnail X size		(1 byte)
   * Thumbnail Y size		(1 byte)
   */
  
  emit_marker(cinfo, M_APP0);
  
  emit_2bytes(cinfo, 2 + 4 + 1 + 2 + 1 + 2 + 2 + 1 + 1); /* length */

  emit_byte(cinfo, 0x4A);	/* Identifier: ASCII "JFIF" */
  emit_byte(cinfo, 0x46);
  emit_byte(cinfo, 0x49);
  emit_byte(cinfo, 0x46);
  emit_byte(cinfo, 0);
  /* We currently emit version code 1.01 since we use no 1.02 features.
   * This may avoid complaints from some older decoders.
   */
  emit_byte(cinfo, 1);		/* Major version */
  emit_byte(cinfo, 1);		/* Minor version */
  emit_byte(cinfo, cinfo->density_unit); /* Pixel size information */
  emit_2bytes(cinfo, (int) cinfo->X_density);
  emit_2bytes(cinfo, (int) cinfo->Y_density);
  emit_byte(cinfo, 0);		/* No thumbnail image */
  emit_byte(cinfo, 0);
}


LOCAL(void)
emit_adobe_app14 (j_compress_ptr cinfo)
/* Emit an Adobe APP14 marker */
{
  /*
   * Length of APP14 block	(2 bytes)
   * Block ID			(5 bytes - ASCII "Adobe")
   * Version Number		(2 bytes - currently 100)
   * Flags0			(2 bytes - currently 0)
   * Flags1			(2 bytes - currently 0)
   * Color transform		(1 byte)
   *
   * Although Adobe TN 5116 mentions Version = 101, all the Adobe files
   * now in circulation seem to use Version = 100, so that's what we write.
   *
   * We write the color transform byte as 1 if the JPEG color space is
   * YCbCr, 2 if it's YCCK, 0 otherwise.  Adobe's definition has to do with
   * whether the encoder performed a transformation, which is pretty useless.
   */
  
  emit_marker(cinfo, M_APP14);
  
  emit_2bytes(cinfo, 2 + 5 + 2 + 2 + 2 + 1); /* length */

  emit_byte(cinfo, 0x41);	/* Identifier: ASCII "Adobe" */
  emit_byte(cinfo, 0x64);
  emit_byte(cinfo, 0x6F);
  emit_byte(cinfo, 0x62);
  emit_byte(cinfo, 0x65);
  emit_2bytes(cinfo, 100);	/* Version */
  emit_2bytes(cinfo, 0);	/* Flags0 */
  emit_2bytes(cinfo, 0);	/* Flags1 */
  switch (cinfo->jpeg_color_space) {
  case JCS_YCbCr:
    emit_byte(cinfo, 1);	/* Color transform = 1 */
    break;
  case JCS_YCCK:
    emit_byte(cinfo, 2);	/* Color transform = 2 */
    break;
  default:
    emit_byte(cinfo, 0);	/* Color transform = 0 */
    break;
  }
}


/*
 * This routine is exported for possible use by applications.
 * The intended use is to emit COM or APPn markers after calling
 * jpeg_start_compress() and before the first jpeg_write_scanlines() call
 * (hence, after write_file_header but before write_frame_header).
 * Other uses are not guaranteed to produce desirable results.
 */

METHODDEF(void)
write_any_marker (j_compress_ptr cinfo, int marker,
		  const JOCTET *dataptr, unsigned int datalen)
/* Emit an arbitrary marker with parameters */
{
  if (datalen <= (unsigned int) 65533) { /* safety check */
    emit_marker(cinfo, (JPEG_MARKER) marker);
  
    emit_2bytes(cinfo, (int) (datalen + 2)); /* total length */

    while (datalen--) {
      emit_byte(cinfo, *dataptr);
      dataptr++;
    }
  }
}


/*
 * Write datastream header.
 * This consists of an SOI and optional APPn markers.
 * We recommend use of the JFIF marker, but not the Adobe marker,
 * when using YCbCr or grayscale data.  The JFIF marker should NOT
 * be used for any other JPEG colorspace.  The Adobe marker is helpful
 * to distinguish RGB, CMYK, and YCCK colorspaces.
 * Note that an application can write additional header markers after
 * jpeg_start_compress returns.
 */

METHODDEF(void)
write_file_header (j_compress_ptr cinfo)
{
  emit_marker(cinfo, M_SOI);	/* first the SOI */

  if (cinfo->write_JFIF_header)	/* next an optional JFIF APP0 */
    emit_jfif_app0(cinfo);
  if (cinfo->write_Adobe_marker) /* next an optional Adobe APP14 */
    emit_adobe_app14(cinfo);
}


/*
 * Write frame header.
 * This consists of DQT and SOFn markers.
 * Note that we do not emit the SOF until we have emitted the DQT(s).
 * This avoids compatibility problems with incorrect implementations that
 * try to error-check the quant table numbers as soon as they see the SOF.
 */

METHODDEF(void)
write_frame_header (j_compress_ptr cinfo)
{
  int ci, prec;
  boolean is_baseline;
  jpeg_component_info *compptr;
  
  /* Emit DQT for each quantization table.
   * Note that emit_dqt() suppresses any duplicate tables.
   */
  prec = 0;
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    prec += emit_dqt(cinfo, compptr->quant_tbl_no);
  }
  /* now prec is nonzero iff there are any 16-bit quant tables. */

  /* Check for a non-baseline specification.
   * Note we assume that Huffman table numbers won't be changed later.
   */
  if (cinfo->arith_code || cinfo->progressive_mode ||
      cinfo->data_precision != 8) {
    is_baseline = FALSE;
  } else {
    is_baseline = TRUE;
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	 ci++, compptr++) {
      if (compptr->dc_tbl_no > 1 || compptr->ac_tbl_no > 1)
	is_baseline = FALSE;
    }
    if (prec && is_baseline) {
      is_baseline = FALSE;
      /* If it's baseline except for quantizer size, warn the user */
      TRACEMS(cinfo, 0, JTRC_16BIT_TABLES);
    }
  }

  /* Emit the proper SOF marker */
  if (cinfo->arith_code) {
    emit_sof(cinfo, M_SOF9);	/* SOF code for arithmetic coding */
  } else {
    if (cinfo->progressive_mode)
      emit_sof(cinfo, M_SOF2);	/* SOF code for progressive Huffman */
    else if (is_baseline)
      emit_sof(cinfo, M_SOF0);	/* SOF code for baseline implementation */
    else
      emit_sof(cinfo, M_SOF1);	/* SOF code for non-baseline Huffman file */
  }
}


/*
 * Write scan header.
 * This consists of DHT or DAC markers, optional DRI, and SOS.
 * Compressed data will be written following the SOS.
 */

METHODDEF(void)
write_scan_header (j_compress_ptr cinfo)
{
  int i;
  jpeg_component_info *compptr;

  if (cinfo->arith_code) {
    /* Emit arith conditioning info.  We may have some duplication
     * if the file has multiple scans, but it's so small it's hardly
     * worth worrying about.
     */
    emit_dac(cinfo);
  } else {
    /* Emit Huffman tables.
     * Note that emit_dht() suppresses any duplicate tables.
     */
    for (i = 0; i < cinfo->comps_in_scan; i++) {
      compptr = cinfo->cur_comp_info[i];
      if (cinfo->progressive_mode) {
	/* Progressive mode: only DC or only AC tables are used in one scan */
	if (cinfo->Ss == 0) {
	  if (cinfo->Ah == 0)	/* DC needs no table for refinement scan */
	    emit_dht(cinfo, compptr->dc_tbl_no, FALSE);
	} else {
	  emit_dht(cinfo, compptr->ac_tbl_no, TRUE);
	}
      } else {
	/* Sequential mode: need both DC and AC tables */
	emit_dht(cinfo, compptr->dc_tbl_no, FALSE);
	emit_dht(cinfo, compptr->ac_tbl_no, TRUE);
      }
    }
  }

  /* Emit DRI if required --- note that DRI value could change for each scan.
   * If it doesn't, a tiny amount of space is wasted in multiple-scan files.
   * We assume DRI will never be nonzero for one scan and zero for a later one.
   */
  if (cinfo->restart_interval)
    emit_dri(cinfo);

  emit_sos(cinfo);
}


/*
 * Write datastream trailer.
 */

METHODDEF(void)
write_file_trailer (j_compress_ptr cinfo)
{
  emit_marker(cinfo, M_EOI);
}


/*
 * Write an abbreviated table-specification datastream.
 * This consists of SOI, DQT and DHT tables, and EOI.
 * Any table that is defined and not marked sent_table = TRUE will be
 * emitted.  Note that all tables will be marked sent_table = TRUE at exit.
 */

METHODDEF(void)
write_tables_only (j_compress_ptr cinfo)
{
  int i;

  emit_marker(cinfo, M_SOI);

  for (i = 0; i < NUM_QUANT_TBLS; i++) {
    if (cinfo->quant_tbl_ptrs[i] != NULL)
      (void) emit_dqt(cinfo, i);
  }

  if (! cinfo->arith_code) {
    for (i = 0; i < NUM_HUFF_TBLS; i++) {
      if (cinfo->dc_huff_tbl_ptrs[i] != NULL)
	emit_dht(cinfo, i, FALSE);
      if (cinfo->ac_huff_tbl_ptrs[i] != NULL)
	emit_dht(cinfo, i, TRUE);
    }
  }

  emit_marker(cinfo, M_EOI);
}


/*
 * Initialize the marker writer module.
 */

GLOBAL(void)
jinit_marker_writer (j_compress_ptr cinfo)
{
  /* Create the subobject */
  cinfo->marker = (struct jpeg_marker_writer *)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				SIZEOF(struct jpeg_marker_writer));
  /* Initialize method pointers */
  cinfo->marker->write_any_marker = write_any_marker;
  cinfo->marker->write_file_header = write_file_header;
  cinfo->marker->write_frame_header = write_frame_header;
  cinfo->marker->write_scan_header = write_scan_header;
  cinfo->marker->write_file_trailer = write_file_trailer;
  cinfo->marker->write_tables_only = write_tables_only;
}