mozjpeg/jcmarker.c

/*
 * jcmarker.c
 *
 * This file was part of the Independent JPEG Group's software:
 * Copyright (C) 1991-1998, Thomas G. Lane.
 * Modified 2003-2010 by Guido Vollbeding.
 * libjpeg-turbo Modifications:
 * Copyright (C) 2010, D. R. Commander.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains routines to write JPEG datastream markers.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jpegcomp.h"


typedef enum {			/* JPEG marker codes */
  M_SOF0  = 0xc0,
  M_SOF1  = 0xc1,
  M_SOF2  = 0xc2,
  M_SOF3  = 0xc3,

  M_SOF5  = 0xc5,
  M_SOF6  = 0xc6,
  M_SOF7  = 0xc7,

  M_JPG   = 0xc8,
  M_SOF9  = 0xc9,
  M_SOF10 = 0xca,
  M_SOF11 = 0xcb,

  M_SOF13 = 0xcd,
  M_SOF14 = 0xce,
  M_SOF15 = 0xcf,

  M_DHT   = 0xc4,

  M_DAC   = 0xcc,

  M_RST0  = 0xd0,
  M_RST1  = 0xd1,
  M_RST2  = 0xd2,
  M_RST3  = 0xd3,
  M_RST4  = 0xd4,
  M_RST5  = 0xd5,
  M_RST6  = 0xd6,
  M_RST7  = 0xd7,

  M_SOI   = 0xd8,
  M_EOI   = 0xd9,
  M_SOS   = 0xda,
  M_DQT   = 0xdb,
  M_DNL   = 0xdc,
  M_DRI   = 0xdd,
  M_DHP   = 0xde,
  M_EXP   = 0xdf,

  M_APP0  = 0xe0,
  M_APP1  = 0xe1,
  M_APP2  = 0xe2,
  M_APP3  = 0xe3,
  M_APP4  = 0xe4,
  M_APP5  = 0xe5,
  M_APP6  = 0xe6,
  M_APP7  = 0xe7,
  M_APP8  = 0xe8,
  M_APP9  = 0xe9,
  M_APP10 = 0xea,
  M_APP11 = 0xeb,
  M_APP12 = 0xec,
  M_APP13 = 0xed,
  M_APP14 = 0xee,
  M_APP15 = 0xef,

  M_JPG0  = 0xf0,
  M_JPG13 = 0xfd,
  M_COM   = 0xfe,

  M_TEM   = 0x01,

  M_ERROR = 0x100
} JPEG_MARKER;


/* Private state */

typedef struct {
  struct jpeg_marker_writer pub; /* public fields */

  unsigned int last_restart_interval; /* last DRI value emitted; 0 after SOI */
} my_marker_writer;

typedef my_marker_writer * my_marker_ptr;


/*
 * Basic output routines.
 *
 * Note that we do not support suspension while writing a marker.
 * Therefore, an application using suspension must ensure that there is
 * enough buffer space for the initial markers (typ. 600-700 bytes) before
 * calling jpeg_start_compress, and enough space to write the trailing EOI
 * (a few bytes) before calling jpeg_finish_compress.  Multipass compression
 * modes are not supported at all with suspension, so those two are the only
 * points where markers will be written.
 */

LOCAL(void)
emit_byte (j_compress_ptr cinfo, int val)
/* Emit a byte */
{
  struct jpeg_destination_mgr * dest = cinfo->dest;

  *(dest->next_output_byte)++ = (JOCTET) val;
  if (--dest->free_in_buffer == 0) {
    if (! (*dest->empty_output_buffer) (cinfo))
      ERREXIT(cinfo, JERR_CANT_SUSPEND);
  }
}


LOCAL(void)
emit_marker (j_compress_ptr cinfo, JPEG_MARKER mark)
/* Emit a marker code */
{
  emit_byte(cinfo, 0xFF);
  emit_byte(cinfo, (int) mark);
}


LOCAL(void)
emit_2bytes (j_compress_ptr cinfo, int value)
/* Emit a 2-byte integer; these are always MSB first in JPEG files */
{
  emit_byte(cinfo, (value >> 8) & 0xFF);
  emit_byte(cinfo, value & 0xFF);
}


/*
 * Routines to write specific marker types.
 */

LOCAL(int)
emit_dqt (j_compress_ptr cinfo, int index)
/* Emit a DQT marker */
/* Returns the precision used (0 = 8bits, 1 = 16bits) for baseline checking */
{
  JQUANT_TBL * qtbl = cinfo->quant_tbl_ptrs[index];
  int prec;
  int i;

  if (qtbl == NULL)
    ERREXIT1(cinfo, JERR_NO_QUANT_TABLE, index);

  prec = 0;
  for (i = 0; i < DCTSIZE2; i++) {
    if (qtbl->quantval[i] > 255)
      prec = 1;
  }

  if (! qtbl->sent_table) {
    emit_marker(cinfo, M_DQT);

    emit_2bytes(cinfo, prec ? DCTSIZE2*2 + 1 + 2 : DCTSIZE2 + 1 + 2);

    emit_byte(cinfo, index + (prec<<4));

    for (i = 0; i < DCTSIZE2; i++) {
      /* The table entries must be emitted in zigzag order. */
      unsigned int qval = qtbl->quantval[jpeg_natural_order[i]];
      if (prec)
	emit_byte(cinfo, (int) (qval >> 8));
      emit_byte(cinfo, (int) (qval & 0xFF));
    }

    qtbl->sent_table = TRUE;
  }

  return prec;
}

LOCAL(int)
emit_multi_dqt (j_compress_ptr cinfo)
/* Emits a DQT marker containing all quantization tables */
/* Returns number of emitted 16-bit tables, or -1 for failed for baseline checking. */
{
  int prec[MAX_COMPONENTS];
  int seen[MAX_COMPONENTS] = { 0 };
  int fin_prec = 0;
  int ci;

  for (ci = 0; ci < cinfo->num_components; ci++) {
    int tbl_num = cinfo->comp_info[ci].quant_tbl_no;
    int i;
    JQUANT_TBL * qtbl = cinfo->quant_tbl_ptrs[tbl_num];

    if (qtbl == NULL || qtbl->sent_table == TRUE)
      return -1;

    prec[ci] = 0;
    for (i = 0; i < DCTSIZE2; i++)
      prec[ci] = !!(prec[ci] + (qtbl->quantval[i] > 255));

    fin_prec += prec[ci];
  }

  emit_marker(cinfo, M_DQT);

  int size = 0;
  for (ci = 0; ci < cinfo->num_components; ci++) {
    int tbl_num = cinfo->comp_info[ci].quant_tbl_no;

    if (!seen[tbl_num]) {
      size += DCTSIZE2 * (prec[ci] + 1) + 1;
      seen[tbl_num] = 1;
    }
  }
  size += 2;

  emit_2bytes(cinfo, size);

  for (ci = 0; ci < cinfo->num_components; ci++) {
    int tbl_num = cinfo->comp_info[ci].quant_tbl_no;
    int i;
    JQUANT_TBL * qtbl = cinfo->quant_tbl_ptrs[tbl_num];

    if (qtbl->sent_table == TRUE)
        continue;

    emit_byte(cinfo, tbl_num + (prec[ci] << 4));

    for (i = 0; i < DCTSIZE2; i++) {
      unsigned int qval = qtbl->quantval[jpeg_natural_order[i]];

      if (prec[ci])
        emit_byte(cinfo, (int) (qval >> 8));
      emit_byte(cinfo, (int) (qval & 0xFF));
    }

    qtbl->sent_table = TRUE;
  }

  return fin_prec;
}

LOCAL(void)
emit_dht (j_compress_ptr cinfo, int index, boolean is_ac)
/* Emit a DHT marker */
{
  JHUFF_TBL * htbl;
  int length, i;
  
  if (is_ac) {
    htbl = cinfo->ac_huff_tbl_ptrs[index];
    index += 0x10;		/* output index has AC bit set */
  } else {
    htbl = cinfo->dc_huff_tbl_ptrs[index];
  }

  if (htbl == NULL)
    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, index);
  
  if (! htbl->sent_table) {
    emit_marker(cinfo, M_DHT);
    
    length = 0;
    for (i = 1; i <= 16; i++)
      length += htbl->bits[i];
    
    emit_2bytes(cinfo, length + 2 + 1 + 16);
    emit_byte(cinfo, index);
    
    for (i = 1; i <= 16; i++)
      emit_byte(cinfo, htbl->bits[i]);
    
    for (i = 0; i < length; i++)
      emit_byte(cinfo, htbl->huffval[i]);
    
    htbl->sent_table = TRUE;
  }
}

LOCAL(boolean)
emit_multi_dht (j_compress_ptr cinfo)
/* Emit all DHT markers */
/* Returns FALSE on failure, TRUE otherwise. */
{
  int i, j;
  int length = 2;
  int dclens[NUM_HUFF_TBLS] = { 0 };
  int aclens[NUM_HUFF_TBLS] = { 0 };
  JHUFF_TBL *dcseen[NUM_HUFF_TBLS] = { NULL };
  JHUFF_TBL *acseen[NUM_HUFF_TBLS] = { NULL };

  /* Calclate the total length. */
  for (i = 0; i < cinfo->comps_in_scan; i++) {
    jpeg_component_info *compptr = cinfo->cur_comp_info[i];
    int dcidx = compptr->dc_tbl_no;
    int acidx = compptr->ac_tbl_no;
    JHUFF_TBL *dctbl = cinfo->dc_huff_tbl_ptrs[dcidx];
    JHUFF_TBL *actbl = cinfo->ac_huff_tbl_ptrs[acidx];
    int seen = 0;

    /* Handle DC table lenghts */
    if (cinfo->Ss == 0 && cinfo->Ah == 0) {
      if (dctbl == NULL)
        ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dcidx);

      if (dctbl->sent_table)
          continue;

      for (j = 0; j < NUM_HUFF_TBLS; j++)
          seen += (dctbl == dcseen[j]);
      if (seen)
          continue;
      dcseen[i] = dctbl;

      for (j = 1; j <= 16; j++)
        dclens[i] += dctbl->bits[j];
      length += dclens[i] + 16 + 1;
    }

    /* Handle AC table lengths */
    if (cinfo->Se) {
      if (actbl == NULL)
        ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, acidx + 0x10);

      if (actbl->sent_table)
          continue;

      seen = 0;
      for (j = 0; j < NUM_HUFF_TBLS; j++)
          seen += (actbl == acseen[j]);
      if (seen)
          continue;
      acseen[i] = actbl;

      for (j = 1; j <= 16; j++)
        aclens[i] += actbl->bits[j];
      length += aclens[i] + 16 + 1;

    }
  }

  /* Make sure we can fit it all into one DHT marker */
  if (length > (1 << 16) - 1)
    return FALSE;

  emit_marker(cinfo, M_DHT);
  emit_2bytes(cinfo, length);

  for (i = 0; i < cinfo->comps_in_scan; i++) {
    jpeg_component_info *compptr = cinfo->cur_comp_info[i];
    int dcidx = compptr->dc_tbl_no;
    int acidx = compptr->ac_tbl_no;
    JHUFF_TBL *dctbl = cinfo->dc_huff_tbl_ptrs[dcidx];
    JHUFF_TBL *actbl = cinfo->ac_huff_tbl_ptrs[acidx];

    acidx += 0x10;

    /* DC */
    if (cinfo->Ss == 0 && cinfo->Ah == 0 && !dctbl->sent_table) {
      emit_byte(cinfo, dcidx);

      for (j = 1; j <= 16; j++)
        emit_byte(cinfo, dctbl->bits[j]);

      for (j = 0; j < dclens[i]; j++)
        emit_byte(cinfo, dctbl->huffval[j]);

      dctbl->sent_table = TRUE;
    }

    if (cinfo->Se && !actbl->sent_table) {
      emit_byte(cinfo, acidx);

      for (j = 1; j <= 16; j++)
        emit_byte(cinfo, actbl->bits[j]);

      for (j = 0; j < aclens[i]; j++)
        emit_byte(cinfo, actbl->huffval[j]);

      actbl->sent_table = TRUE;
    }
  }

  return TRUE;
}

LOCAL(void)
emit_dac (j_compress_ptr cinfo)
/* Emit a DAC marker */
/* Since the useful info is so small, we want to emit all the tables in */
/* one DAC marker.  Therefore this routine does its own scan of the table. */
{
#ifdef C_ARITH_CODING_SUPPORTED
  char dc_in_use[NUM_ARITH_TBLS];
  char ac_in_use[NUM_ARITH_TBLS];
  int length, i;
  jpeg_component_info *compptr;

  for (i = 0; i < NUM_ARITH_TBLS; i++)
    dc_in_use[i] = ac_in_use[i] = 0;

  for (i = 0; i < cinfo->comps_in_scan; i++) {
    compptr = cinfo->cur_comp_info[i];
    /* DC needs no table for refinement scan */
    if (cinfo->Ss == 0 && cinfo->Ah == 0)
      dc_in_use[compptr->dc_tbl_no] = 1;
    /* AC needs no table when not present */
    if (cinfo->Se)
      ac_in_use[compptr->ac_tbl_no] = 1;
  }

  length = 0;
  for (i = 0; i < NUM_ARITH_TBLS; i++)
    length += dc_in_use[i] + ac_in_use[i];

  if (length) {
    emit_marker(cinfo, M_DAC);

    emit_2bytes(cinfo, length*2 + 2);

    for (i = 0; i < NUM_ARITH_TBLS; i++) {
      if (dc_in_use[i]) {
	emit_byte(cinfo, i);
	emit_byte(cinfo, cinfo->arith_dc_L[i] + (cinfo->arith_dc_U[i]<<4));
      }
      if (ac_in_use[i]) {
	emit_byte(cinfo, i + 0x10);
	emit_byte(cinfo, cinfo->arith_ac_K[i]);
      }
    }
  }
#endif /* C_ARITH_CODING_SUPPORTED */
}


LOCAL(void)
emit_dri (j_compress_ptr cinfo)
/* Emit a DRI marker */
{
  emit_marker(cinfo, M_DRI);
  
  emit_2bytes(cinfo, 4);	/* fixed length */

  emit_2bytes(cinfo, (int) cinfo->restart_interval);
}


LOCAL(void)
emit_sof (j_compress_ptr cinfo, JPEG_MARKER code)
/* Emit a SOF marker */
{
  int ci;
  jpeg_component_info *compptr;
  
  emit_marker(cinfo, code);
  
  emit_2bytes(cinfo, 3 * cinfo->num_components + 2 + 5 + 1); /* length */

  /* Make sure image isn't bigger than SOF field can handle */
  if ((long) cinfo->_jpeg_height > 65535L ||
      (long) cinfo->_jpeg_width > 65535L)
    ERREXIT1(cinfo, JERR_IMAGE_TOO_BIG, (unsigned int) 65535);

  emit_byte(cinfo, cinfo->data_precision);
  emit_2bytes(cinfo, (int) cinfo->_jpeg_height);
  emit_2bytes(cinfo, (int) cinfo->_jpeg_width);

  emit_byte(cinfo, cinfo->num_components);

  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    emit_byte(cinfo, compptr->component_id);
    emit_byte(cinfo, (compptr->h_samp_factor << 4) + compptr->v_samp_factor);
    emit_byte(cinfo, compptr->quant_tbl_no);
  }
}


LOCAL(void)
emit_sos (j_compress_ptr cinfo)
/* Emit a SOS marker */
{
  int i, td, ta;
  jpeg_component_info *compptr;
  
  emit_marker(cinfo, M_SOS);
  
  emit_2bytes(cinfo, 2 * cinfo->comps_in_scan + 2 + 1 + 3); /* length */
  
  emit_byte(cinfo, cinfo->comps_in_scan);
  
  for (i = 0; i < cinfo->comps_in_scan; i++) {
    compptr = cinfo->cur_comp_info[i];
    emit_byte(cinfo, compptr->component_id);

    /* We emit 0 for unused field(s); this is recommended by the P&M text
     * but does not seem to be specified in the standard.
     */

    /* DC needs no table for refinement scan */
    td = cinfo->Ss == 0 && cinfo->Ah == 0 ? compptr->dc_tbl_no : 0;
    /* AC needs no table when not present */
    ta = cinfo->Se ? compptr->ac_tbl_no : 0;

    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 - major first)
   * 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);
  emit_byte(cinfo, cinfo->JFIF_major_version); /* Version fields */
  emit_byte(cinfo, cinfo->JFIF_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;
  }
}


/*
 * These routines allow writing an arbitrary marker with parameters.
 * The only intended use is to emit COM or APPn markers after calling
 * write_file_header and before calling write_frame_header.
 * Other uses are not guaranteed to produce desirable results.
 * Counting the parameter bytes properly is the caller's responsibility.
 */

METHODDEF(void)
write_marker_header (j_compress_ptr cinfo, int marker, unsigned int datalen)
/* Emit an arbitrary marker header */
{
  if (datalen > (unsigned int) 65533)		/* safety check */
    ERREXIT(cinfo, JERR_BAD_LENGTH);

  emit_marker(cinfo, (JPEG_MARKER) marker);

  emit_2bytes(cinfo, (int) (datalen + 2));	/* total length */
}

METHODDEF(void)
write_marker_byte (j_compress_ptr cinfo, int val)
/* Emit one byte of marker parameters following write_marker_header */
{
  emit_byte(cinfo, val);
}


/*
 * 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)
{
  my_marker_ptr marker = (my_marker_ptr) cinfo->marker;

  emit_marker(cinfo, M_SOI);	/* first the SOI */

  /* SOI is defined to reset restart interval to 0 */
  marker->last_restart_interval = 0;

  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 = emit_multi_dqt(cinfo);
  if (prec == -1) {
    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) {
    if (cinfo->progressive_mode)
      emit_sof(cinfo, M_SOF10); /* SOF code for progressive arithmetic */
    else
      emit_sof(cinfo, M_SOF9);  /* SOF code for sequential arithmetic */
  } 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)
{
  my_marker_ptr marker = (my_marker_ptr) cinfo->marker;
  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.
     */
    if (!emit_multi_dht(cinfo)) {
      for (i = 0; i < cinfo->comps_in_scan; i++) {
        compptr = cinfo->cur_comp_info[i];
        /* DC needs no table for refinement scan */
        if (cinfo->Ss == 0 && cinfo->Ah == 0)
          emit_dht(cinfo, compptr->dc_tbl_no, FALSE);
        /* AC needs no table when not present */
        if (cinfo->Se)
          emit_dht(cinfo, compptr->ac_tbl_no, TRUE);
      }
    }
  }

  /* Emit DRI if required --- note that DRI value could change for each scan.
   * We avoid wasting space with unnecessary DRIs, however.
   */
  if (cinfo->restart_interval != marker->last_restart_interval) {
    emit_dri(cinfo);
    marker->last_restart_interval = cinfo->restart_interval;
  }

  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)
{
  my_marker_ptr marker;

  /* Create the subobject */
  marker = (my_marker_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                sizeof(my_marker_writer));
  cinfo->marker = (struct jpeg_marker_writer *) marker;
  /* Initialize method pointers */
  marker->pub.write_file_header = write_file_header;
  marker->pub.write_frame_header = write_frame_header;
  marker->pub.write_scan_header = write_scan_header;
  marker->pub.write_file_trailer = write_file_trailer;
  marker->pub.write_tables_only = write_tables_only;
  marker->pub.write_marker_header = write_marker_header;
  marker->pub.write_marker_byte = write_marker_byte;
  /* Initialize private state */
  marker->last_restart_interval = 0;
}