jdmarker.c

/*
 * jdmarker.c
 *
 * Copyright (C) 1991-1995, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains routines to decode JPEG datastream markers.
 * Most of the complexity arises from our desire to support input
 * suspension: if not all of the data for a marker is available,
 * we must exit back to the application.  On resumption, we reprocess
 * the marker.
 */

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


/*
 * Macros for fetching data from the data source module.
 *
 * At all times, cinfo->src->next_input_byte and ->bytes_in_buffer reflect
 * the current restart point; we update them only when we have reached a
 * suitable place to restart if a suspension occurs.
 */

/* Declare and initialize local copies of input pointer/count */
#define INPUT_VARS(cinfo)  \
	struct jpeg_source_mgr * datasrc = (cinfo)->src;  \
	const JOCTET * next_input_byte = datasrc->next_input_byte;  \
	size_t bytes_in_buffer = datasrc->bytes_in_buffer

/* Unload the local copies --- do this only at a restart boundary */
#define INPUT_SYNC(cinfo)  \
	( datasrc->next_input_byte = next_input_byte,  \
	  datasrc->bytes_in_buffer = bytes_in_buffer )

/* Reload the local copies --- seldom used except in MAKE_BYTE_AVAIL */
#define INPUT_RELOAD(cinfo)  \
	( next_input_byte = datasrc->next_input_byte,  \
	  bytes_in_buffer = datasrc->bytes_in_buffer )

/* Internal macro for INPUT_BYTE and INPUT_2BYTES: make a byte available.
 * Note we do *not* do INPUT_SYNC before calling fill_input_buffer,
 * but we must reload the local copies after a successful fill.
 */
#define MAKE_BYTE_AVAIL(cinfo,action)  \
	if (bytes_in_buffer == 0) {  \
	  if (! (*datasrc->fill_input_buffer) (cinfo))  \
	    { action; }  \
	  INPUT_RELOAD(cinfo);  \
	}  \
	bytes_in_buffer--

/* Read a byte into variable V.
 * If must suspend, take the specified action (typically "return FALSE").
 */
#define INPUT_BYTE(cinfo,V,action)  \
	MAKESTMT( MAKE_BYTE_AVAIL(cinfo,action); \
		  V = GETJOCTET(*next_input_byte++); )

/* As above, but read two bytes interpreted as an unsigned 16-bit integer.
 * V should be declared unsigned int or perhaps INT32.
 */
#define INPUT_2BYTES(cinfo,V,action)  \
	MAKESTMT( MAKE_BYTE_AVAIL(cinfo,action); \
		  V = ((unsigned int) GETJOCTET(*next_input_byte++)) << 8; \
		  MAKE_BYTE_AVAIL(cinfo,action); \
		  V += GETJOCTET(*next_input_byte++); )


/*
 * Routines to process JPEG markers.
 *
 * Entry condition: JPEG marker itself has been read and its code saved
 *   in cinfo->unread_marker; input restart point is just after the marker.
 *
 * Exit: if return TRUE, have read and processed any parameters, and have
 *   updated the restart point to point after the parameters.
 *   If return FALSE, was forced to suspend before reaching end of
 *   marker parameters; restart point has not been moved.  Same routine
 *   will be called again after application supplies more input data.
 *
 * This approach to suspension assumes that all of a marker's parameters can
 * fit into a single input bufferload.  This should hold for "normal"
 * markers.  Some COM/APPn markers might have large parameter segments,
 * but we use skip_input_data to get past those, and thereby put the problem
 * on the source manager's shoulders.
 *
 * Note that we don't bother to avoid duplicate trace messages if a
 * suspension occurs within marker parameters.  Other side effects
 * require more care.
 */


LOCAL boolean
get_soi (j_decompress_ptr cinfo)
/* Process an SOI marker */
{
  int i;
  
  TRACEMS(cinfo, 1, JTRC_SOI);

  if (cinfo->marker->saw_SOI)
    ERREXIT(cinfo, JERR_SOI_DUPLICATE);

  /* Reset all parameters that are defined to be reset by SOI */

  for (i = 0; i < NUM_ARITH_TBLS; i++) {
    cinfo->arith_dc_L[i] = 0;
    cinfo->arith_dc_U[i] = 1;
    cinfo->arith_ac_K[i] = 5;
  }
  cinfo->restart_interval = 0;

  /* Set initial assumptions for colorspace etc */

  cinfo->jpeg_color_space = JCS_UNKNOWN;
  cinfo->CCIR601_sampling = FALSE; /* Assume non-CCIR sampling??? */

  cinfo->saw_JFIF_marker = FALSE;
  cinfo->density_unit = 0;	/* set default JFIF APP0 values */
  cinfo->X_density = 1;
  cinfo->Y_density = 1;
  cinfo->saw_Adobe_marker = FALSE;
  cinfo->Adobe_transform = 0;

  cinfo->marker->saw_SOI = TRUE;

  return TRUE;
}


LOCAL boolean
get_sof (j_decompress_ptr cinfo, boolean is_prog, boolean is_arith)
/* Process a SOFn marker */
{
  INT32 length;
  int c, ci;
  jpeg_component_info * compptr;
  INPUT_VARS(cinfo);

  cinfo->progressive_mode = is_prog;
  cinfo->arith_code = is_arith;

  INPUT_2BYTES(cinfo, length, return FALSE);

  INPUT_BYTE(cinfo, cinfo->data_precision, return FALSE);
  INPUT_2BYTES(cinfo, cinfo->image_height, return FALSE);
  INPUT_2BYTES(cinfo, cinfo->image_width, return FALSE);
  INPUT_BYTE(cinfo, cinfo->num_components, return FALSE);

  length -= 8;

  TRACEMS4(cinfo, 1, JTRC_SOF, cinfo->unread_marker,
	   (int) cinfo->image_width, (int) cinfo->image_height,
	   cinfo->num_components);

  if (cinfo->marker->saw_SOF)
    ERREXIT(cinfo, JERR_SOF_DUPLICATE);

  /* We don't support files in which the image height is initially specified */
  /* as 0 and is later redefined by DNL.  As long as we have to check that,  */
  /* might as well have a general sanity check. */
  if (cinfo->image_height <= 0 || cinfo->image_width <= 0
      || cinfo->num_components <= 0)
    ERREXIT(cinfo, JERR_EMPTY_IMAGE);

  if (length != (cinfo->num_components * 3))
    ERREXIT(cinfo, JERR_BAD_LENGTH);

  if (cinfo->comp_info == NULL)	/* do only once, even if suspend */
    cinfo->comp_info = (jpeg_component_info *) (*cinfo->mem->alloc_small)
			((j_common_ptr) cinfo, JPOOL_IMAGE,
			 cinfo->num_components * SIZEOF(jpeg_component_info));
  
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
       ci++, compptr++) {
    compptr->component_index = ci;
    INPUT_BYTE(cinfo, compptr->component_id, return FALSE);
    INPUT_BYTE(cinfo, c, return FALSE);
    compptr->h_samp_factor = (c >> 4) & 15;
    compptr->v_samp_factor = (c     ) & 15;
    INPUT_BYTE(cinfo, compptr->quant_tbl_no, return FALSE);

    TRACEMS4(cinfo, 1, JTRC_SOF_COMPONENT,
	     compptr->component_id, compptr->h_samp_factor,
	     compptr->v_samp_factor, compptr->quant_tbl_no);
  }

  cinfo->marker->saw_SOF = TRUE;

  INPUT_SYNC(cinfo);
  return TRUE;
}


LOCAL boolean
get_sos (j_decompress_ptr cinfo)
/* Process a SOS marker */
{
  INT32 length;
  int i, ci, n, c, cc;
  jpeg_component_info * compptr;
  INPUT_VARS(cinfo);

  if (! cinfo->marker->saw_SOF)
    ERREXIT(cinfo, JERR_SOS_NO_SOF);

  INPUT_2BYTES(cinfo, length, return FALSE);

  INPUT_BYTE(cinfo, n, return FALSE); /* Number of components */

  if (length != (n * 2 + 6) || n < 1 || n > MAX_COMPS_IN_SCAN)
    ERREXIT(cinfo, JERR_BAD_LENGTH);

  TRACEMS1(cinfo, 1, JTRC_SOS, n);

  cinfo->comps_in_scan = n;

  /* Collect the component-spec parameters */

  for (i = 0; i < n; i++) {
    INPUT_BYTE(cinfo, cc, return FALSE);
    INPUT_BYTE(cinfo, c, return FALSE);
    
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	 ci++, compptr++) {
      if (cc == compptr->component_id)
	goto id_found;
    }

    ERREXIT1(cinfo, JERR_BAD_COMPONENT_ID, cc);

  id_found:

    cinfo->cur_comp_info[i] = compptr;
    compptr->dc_tbl_no = (c >> 4) & 15;
    compptr->ac_tbl_no = (c     ) & 15;
    
    TRACEMS3(cinfo, 1, JTRC_SOS_COMPONENT, cc,
	     compptr->dc_tbl_no, compptr->ac_tbl_no);
  }

  /* Collect the additional scan parameters Ss, Se, Ah/Al. */
  INPUT_BYTE(cinfo, c, return FALSE);
  cinfo->Ss = c;
  INPUT_BYTE(cinfo, c, return FALSE);
  cinfo->Se = c;
  INPUT_BYTE(cinfo, c, return FALSE);
  cinfo->Ah = (c >> 4) & 15;
  cinfo->Al = (c     ) & 15;

  TRACEMS4(cinfo, 1, JTRC_SOS_PARAMS, cinfo->Ss, cinfo->Se,
	   cinfo->Ah, cinfo->Al);

  /* Prepare to scan data & restart markers */
  cinfo->marker->next_restart_num = 0;

  /* Count another SOS marker */
  cinfo->input_scan_number++;

  INPUT_SYNC(cinfo);
  return TRUE;
}


METHODDEF boolean
get_app0 (j_decompress_ptr cinfo)
/* Process an APP0 marker */
{
#define JFIF_LEN 14
  INT32 length;
  UINT8 b[JFIF_LEN];
  int buffp;
  INPUT_VARS(cinfo);

  INPUT_2BYTES(cinfo, length, return FALSE);
  length -= 2;

  /* See if a JFIF APP0 marker is present */

  if (length >= JFIF_LEN) {
    for (buffp = 0; buffp < JFIF_LEN; buffp++)
      INPUT_BYTE(cinfo, b[buffp], return FALSE);
    length -= JFIF_LEN;

    if (b[0]==0x4A && b[1]==0x46 && b[2]==0x49 && b[3]==0x46 && b[4]==0) {
      /* Found JFIF APP0 marker: check version */
      /* Major version must be 1, anything else signals an incompatible change.
       * We used to treat this as an error, but now it's a nonfatal warning,
       * because some bozo at Hijaak couldn't read the spec.
       * Minor version should be 0..2, but process anyway if newer.
       */
      if (b[5] != 1)
	WARNMS2(cinfo, JWRN_JFIF_MAJOR, b[5], b[6]);
      else if (b[6] > 2)
	TRACEMS2(cinfo, 1, JTRC_JFIF_MINOR, b[5], b[6]);
      /* Save info */
      cinfo->saw_JFIF_marker = TRUE;
      cinfo->density_unit = b[7];
      cinfo->X_density = (b[8] << 8) + b[9];
      cinfo->Y_density = (b[10] << 8) + b[11];
      TRACEMS3(cinfo, 1, JTRC_JFIF,
	       cinfo->X_density, cinfo->Y_density, cinfo->density_unit);
      if (b[12] | b[13])
	TRACEMS2(cinfo, 1, JTRC_JFIF_THUMBNAIL, b[12], b[13]);
      if (length != ((INT32) b[12] * (INT32) b[13] * (INT32) 3))
	TRACEMS1(cinfo, 1, JTRC_JFIF_BADTHUMBNAILSIZE, (int) length);
    } else {
      /* Start of APP0 does not match "JFIF" */
      TRACEMS1(cinfo, 1, JTRC_APP0, (int) length + JFIF_LEN);
    }
  } else {
    /* Too short to be JFIF marker */
    TRACEMS1(cinfo, 1, JTRC_APP0, (int) length);
  }

  INPUT_SYNC(cinfo);
  if (length > 0)		/* skip any remaining data -- could be lots */
    (*cinfo->src->skip_input_data) (cinfo, (long) length);

  return TRUE;
}


METHODDEF boolean
get_app14 (j_decompress_ptr cinfo)
/* Process an APP14 marker */
{
#define ADOBE_LEN 12
  INT32 length;
  UINT8 b[ADOBE_LEN];
  int buffp;
  unsigned int version, flags0, flags1, transform;
  INPUT_VARS(cinfo);

  INPUT_2BYTES(cinfo, length, return FALSE);
  length -= 2;

  /* See if an Adobe APP14 marker is present */

  if (length >= ADOBE_LEN) {
    for (buffp = 0; buffp < ADOBE_LEN; buffp++)
      INPUT_BYTE(cinfo, b[buffp], return FALSE);
    length -= ADOBE_LEN;

    if (b[0]==0x41 && b[1]==0x64 && b[2]==0x6F && b[3]==0x62 && b[4]==0x65) {
      /* Found Adobe APP14 marker */
      version = (b[5] << 8) + b[6];
      flags0 = (b[7] << 8) + b[8];
      flags1 = (b[9] << 8) + b[10];
      transform = b[11];
      TRACEMS4(cinfo, 1, JTRC_ADOBE, version, flags0, flags1, transform);
      cinfo->saw_Adobe_marker = TRUE;
      cinfo->Adobe_transform = (UINT8) transform;
    } else {
      /* Start of APP14 does not match "Adobe" */
      TRACEMS1(cinfo, 1, JTRC_APP14, (int) length + ADOBE_LEN);
    }
  } else {
    /* Too short to be Adobe marker */
    TRACEMS1(cinfo, 1, JTRC_APP14, (int) length);
  }

  INPUT_SYNC(cinfo);
  if (length > 0)		/* skip any remaining data -- could be lots */
    (*cinfo->src->skip_input_data) (cinfo, (long) length);

  return TRUE;
}


LOCAL boolean
get_dac (j_decompress_ptr cinfo)
/* Process a DAC marker */
{
  INT32 length;
  int index, val;
  INPUT_VARS(cinfo);

  INPUT_2BYTES(cinfo, length, return FALSE);
  length -= 2;
  
  while (length > 0) {
    INPUT_BYTE(cinfo, index, return FALSE);
    INPUT_BYTE(cinfo, val, return FALSE);

    length -= 2;

    TRACEMS2(cinfo, 1, JTRC_DAC, index, val);

    if (index < 0 || index >= (2*NUM_ARITH_TBLS))
      ERREXIT1(cinfo, JERR_DAC_INDEX, index);

    if (index >= NUM_ARITH_TBLS) { /* define AC table */
      cinfo->arith_ac_K[index-NUM_ARITH_TBLS] = (UINT8) val;
    } else {			/* define DC table */
      cinfo->arith_dc_L[index] = (UINT8) (val & 0x0F);
      cinfo->arith_dc_U[index] = (UINT8) (val >> 4);
      if (cinfo->arith_dc_L[index] > cinfo->arith_dc_U[index])
	ERREXIT1(cinfo, JERR_DAC_VALUE, val);
    }
  }

  INPUT_SYNC(cinfo);
  return TRUE;
}


LOCAL boolean
get_dht (j_decompress_ptr cinfo)
/* Process a DHT marker */
{
  INT32 length;
  UINT8 bits[17];
  UINT8 huffval[256];
  int i, index, count;
  JHUFF_TBL **htblptr;
  INPUT_VARS(cinfo);

  INPUT_2BYTES(cinfo, length, return FALSE);
  length -= 2;
  
  while (length > 0) {
    INPUT_BYTE(cinfo, index, return FALSE);

    TRACEMS1(cinfo, 1, JTRC_DHT, index);
      
    bits[0] = 0;
    count = 0;
    for (i = 1; i <= 16; i++) {
      INPUT_BYTE(cinfo, bits[i], return FALSE);
      count += bits[i];
    }

    length -= 1 + 16;

    TRACEMS8(cinfo, 2, JTRC_HUFFBITS,
	     bits[1], bits[2], bits[3], bits[4],
	     bits[5], bits[6], bits[7], bits[8]);
    TRACEMS8(cinfo, 2, JTRC_HUFFBITS,
	     bits[9], bits[10], bits[11], bits[12],
	     bits[13], bits[14], bits[15], bits[16]);

    if (count > 256 || ((INT32) count) > length)
      ERREXIT(cinfo, JERR_DHT_COUNTS);

    for (i = 0; i < count; i++)
      INPUT_BYTE(cinfo, huffval[i], return FALSE);

    length -= count;

    if (index & 0x10) {		/* AC table definition */
      index -= 0x10;
      htblptr = &cinfo->ac_huff_tbl_ptrs[index];
    } else {			/* DC table definition */
      htblptr = &cinfo->dc_huff_tbl_ptrs[index];
    }

    if (index < 0 || index >= NUM_HUFF_TBLS)
      ERREXIT1(cinfo, JERR_DHT_INDEX, index);

    if (*htblptr == NULL)
      *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
  
    MEMCOPY((*htblptr)->bits, bits, SIZEOF((*htblptr)->bits));
    MEMCOPY((*htblptr)->huffval, huffval, SIZEOF((*htblptr)->huffval));
  }

  INPUT_SYNC(cinfo);
  return TRUE;
}


LOCAL boolean
get_dqt (j_decompress_ptr cinfo)
/* Process a DQT marker */
{
  INT32 length;
  int n, i, prec;
  unsigned int tmp;
  JQUANT_TBL *quant_ptr;
  INPUT_VARS(cinfo);

  INPUT_2BYTES(cinfo, length, return FALSE);
  length -= 2;

  while (length > 0) {
    INPUT_BYTE(cinfo, n, return FALSE);
    prec = n >> 4;
    n &= 0x0F;

    TRACEMS2(cinfo, 1, JTRC_DQT, n, prec);

    if (n >= NUM_QUANT_TBLS)
      ERREXIT1(cinfo, JERR_DQT_INDEX, n);
      
    if (cinfo->quant_tbl_ptrs[n] == NULL)
      cinfo->quant_tbl_ptrs[n] = jpeg_alloc_quant_table((j_common_ptr) cinfo);
    quant_ptr = cinfo->quant_tbl_ptrs[n];

    for (i = 0; i < DCTSIZE2; i++) {
      if (prec)
	INPUT_2BYTES(cinfo, tmp, return FALSE);
      else
	INPUT_BYTE(cinfo, tmp, return FALSE);
      quant_ptr->quantval[i] = (UINT16) tmp;
    }

    for (i = 0; i < DCTSIZE2; i += 8) {
      TRACEMS8(cinfo, 2, JTRC_QUANTVALS,
	       quant_ptr->quantval[i  ], quant_ptr->quantval[i+1],
	       quant_ptr->quantval[i+2], quant_ptr->quantval[i+3],
	       quant_ptr->quantval[i+4], quant_ptr->quantval[i+5],
	       quant_ptr->quantval[i+6], quant_ptr->quantval[i+7]);
    }

    length -= DCTSIZE2+1;
    if (prec) length -= DCTSIZE2;
  }

  INPUT_SYNC(cinfo);
  return TRUE;
}


LOCAL boolean
get_dri (j_decompress_ptr cinfo)
/* Process a DRI marker */
{
  INT32 length;
  unsigned int tmp;
  INPUT_VARS(cinfo);

  INPUT_2BYTES(cinfo, length, return FALSE);
  
  if (length != 4)
    ERREXIT(cinfo, JERR_BAD_LENGTH);

  INPUT_2BYTES(cinfo, tmp, return FALSE);

  TRACEMS1(cinfo, 1, JTRC_DRI, tmp);

  cinfo->restart_interval = tmp;

  INPUT_SYNC(cinfo);
  return TRUE;
}


METHODDEF boolean
skip_variable (j_decompress_ptr cinfo)
/* Skip over an unknown or uninteresting variable-length marker */
{
  INT32 length;
  INPUT_VARS(cinfo);

  INPUT_2BYTES(cinfo, length, return FALSE);
  
  TRACEMS2(cinfo, 1, JTRC_MISC_MARKER, cinfo->unread_marker, (int) length);

  INPUT_SYNC(cinfo);		/* do before skip_input_data */
  (*cinfo->src->skip_input_data) (cinfo, (long) length - 2L);

  return TRUE;
}


/*
 * Find the next JPEG marker, save it in cinfo->unread_marker.
 * Returns FALSE if had to suspend before reaching a marker;
 * in that case cinfo->unread_marker is unchanged.
 *
 * Note that the result might not be a valid marker code,
 * but it will never be 0 or FF.
 */

LOCAL boolean
next_marker (j_decompress_ptr cinfo)
{
  int c;
  INPUT_VARS(cinfo);

  for (;;) {
    INPUT_BYTE(cinfo, c, return FALSE);
    /* Skip any non-FF bytes.
     * This may look a bit inefficient, but it will not occur in a valid file.
     * We sync after each discarded byte so that a suspending data source
     * can discard the byte from its buffer.
     */
    while (c != 0xFF) {
      cinfo->marker->discarded_bytes++;
      INPUT_SYNC(cinfo);
      INPUT_BYTE(cinfo, c, return FALSE);
    }
    /* This loop swallows any duplicate FF bytes.  Extra FFs are legal as
     * pad bytes, so don't count them in discarded_bytes.  We assume there
     * will not be so many consecutive FF bytes as to overflow a suspending
     * data source's input buffer.
     */
    do {
      INPUT_BYTE(cinfo, c, return FALSE);
    } while (c == 0xFF);
    if (c != 0)
      break;			/* found a valid marker, exit loop */
    /* Reach here if we found a stuffed-zero data sequence (FF/00).
     * Discard it and loop back to try again.
     */
    cinfo->marker->discarded_bytes += 2;
    INPUT_SYNC(cinfo);
  }

  if (cinfo->marker->discarded_bytes != 0) {
    WARNMS2(cinfo, JWRN_EXTRANEOUS_DATA, cinfo->marker->discarded_bytes, c);
    cinfo->marker->discarded_bytes = 0;
  }

  cinfo->unread_marker = c;

  INPUT_SYNC(cinfo);
  return TRUE;
}


LOCAL boolean
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, 2, 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);
}