jddiffct.c - external/github.com/libjpeg-turbo/libjpeg-turbo - Git at Google

 /*
  * jddiffct.c
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1994-1997, Thomas G. Lane.
  * Lossless JPEG Modifications:
  * Copyright (C) 1999, Ken Murchison.
  * libjpeg-turbo Modifications:
  * Copyright (C) 2022, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
  * This file contains the [un]difference buffer controller for decompression.
  * This controller is the top level of the lossless JPEG decompressor proper.
  * The difference buffer lies between the entropy decoding and
  * prediction/undifferencing steps.  The undifference buffer lies between the
  * prediction/undifferencing and scaling steps.
  *
  * In buffered-image mode, this controller is the interface between
  * input-oriented processing and output-oriented processing.
  */

 #define JPEG_INTERNALS
 #include "jinclude.h"
 #include "jpeglib.h"
 #include "jlossls.h"            /* Private declarations for lossless codec */


 #ifdef D_LOSSLESS_SUPPORTED

 /* Private buffer controller object */

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

   /* These variables keep track of the current location of the input side. */
   /* cinfo->input_iMCU_row is also used for this. */
   JDIMENSION MCU_ctr;           /* counts MCUs processed in current row */
   unsigned int restart_rows_to_go;      /* MCU rows left in this restart
                                            interval */
   unsigned int MCU_vert_offset;         /* counts MCU rows within iMCU row */
   unsigned int MCU_rows_per_iMCU_row;   /* number of such rows needed */

   /* The output side's location is represented by cinfo->output_iMCU_row. */

   JDIFFARRAY diff_buf[MAX_COMPONENTS];  /* iMCU row of differences */
   JDIFFARRAY undiff_buf[MAX_COMPONENTS]; /* iMCU row of undiff'd samples */

 #ifdef D_MULTISCAN_FILES_SUPPORTED
   /* In multi-pass modes, we need a virtual sample array for each component. */
   jvirt_sarray_ptr whole_image[MAX_COMPONENTS];
 #endif
 } my_diff_controller;

 typedef my_diff_controller *my_diff_ptr;

 /* Forward declarations */
 METHODDEF(int) decompress_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf);
 #ifdef D_MULTISCAN_FILES_SUPPORTED
 METHODDEF(int) output_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf);
 #endif


 LOCAL(void)
 start_iMCU_row(j_decompress_ptr cinfo)
 /* Reset within-iMCU-row counters for a new row (input side) */
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

   /* In an interleaved scan, an MCU row is the same as an iMCU row.
    * In a noninterleaved scan, an iMCU row has v_samp_factor MCU rows.
    * But at the bottom of the image, process only what's left.
    */
   if (cinfo->comps_in_scan > 1) {
     diff->MCU_rows_per_iMCU_row = 1;
   } else {
     if (cinfo->input_iMCU_row < (cinfo->total_iMCU_rows-1))
       diff->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->v_samp_factor;
     else
       diff->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->last_row_height;
   }

   diff->MCU_ctr = 0;
   diff->MCU_vert_offset = 0;
 }


 /*
  * Initialize for an input processing pass.
  */

 METHODDEF(void)
 start_input_pass(j_decompress_ptr cinfo)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

   /* Because it is hitching a ride on the jpeg_inverse_dct struct,
    * start_pass_lossless() will be called at the start of the output pass.
    * This ensures that it will be called at the start of the input pass as
    * well.
    */
   (*cinfo->idct->start_pass) (cinfo);

   /* Check that the restart interval is an integer multiple of the number
    * of MCUs in an MCU row.
    */
   if (cinfo->restart_interval % cinfo->MCUs_per_row != 0)
     ERREXIT2(cinfo, JERR_BAD_RESTART,
              cinfo->restart_interval, cinfo->MCUs_per_row);

   /* Initialize restart counter */
   diff->restart_rows_to_go = cinfo->restart_interval / cinfo->MCUs_per_row;

   cinfo->input_iMCU_row = 0;
   start_iMCU_row(cinfo);
 }


 /*
  * Check for a restart marker & resynchronize decoder, undifferencer.
  * Returns FALSE if must suspend.
  */

 METHODDEF(boolean)
 process_restart(j_decompress_ptr cinfo)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

   if (!(*cinfo->entropy->process_restart) (cinfo))
     return FALSE;

   (*cinfo->idct->start_pass) (cinfo);

   /* Reset restart counter */
   diff->restart_rows_to_go = cinfo->restart_interval / cinfo->MCUs_per_row;

   return TRUE;
 }


 /*
  * Initialize for an output processing pass.
  */

 METHODDEF(void)
 start_output_pass(j_decompress_ptr cinfo)
 {
   cinfo->output_iMCU_row = 0;
 }


 /*
  * Decompress and return some data in the supplied buffer.
  * Always attempts to emit one fully interleaved MCU row ("iMCU" row).
  * Input and output must run in lockstep since we have only a one-MCU buffer.
  * Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
  *
  * NB: output_buf contains a plane for each component in image,
  * which we index according to the component's SOF position.
  */

 METHODDEF(int)
 decompress_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
   lossless_decomp_ptr losslessd = (lossless_decomp_ptr)cinfo->idct;
   JDIMENSION MCU_col_num;       /* index of current MCU within row */
   JDIMENSION MCU_count;         /* number of MCUs decoded */
   JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
   int ci, compi, row, prev_row;
   unsigned int yoffset;
   jpeg_component_info *compptr;

   /* Loop to process as much as one whole iMCU row */
   for (yoffset = diff->MCU_vert_offset; yoffset < diff->MCU_rows_per_iMCU_row;
        yoffset++) {

     /* Process restart marker if needed; may have to suspend */
     if (cinfo->restart_interval) {
       if (diff->restart_rows_to_go == 0)
         if (!process_restart(cinfo))
           return JPEG_SUSPENDED;
     }

     MCU_col_num = diff->MCU_ctr;
     /* Try to fetch an MCU row (or remaining portion of suspended MCU row). */
     MCU_count =
       (*cinfo->entropy->decode_mcus) (cinfo,
                                       diff->diff_buf, yoffset, MCU_col_num,
                                       cinfo->MCUs_per_row - MCU_col_num);
     if (MCU_count != cinfo->MCUs_per_row - MCU_col_num) {
       /* Suspension forced; update state counters and exit */
       diff->MCU_vert_offset = yoffset;
       diff->MCU_ctr += MCU_count;
       return JPEG_SUSPENDED;
     }

     /* Account for restart interval (no-op if not using restarts) */
     if (cinfo->restart_interval)
       diff->restart_rows_to_go--;

     /* Completed an MCU row, but perhaps not an iMCU row */
     diff->MCU_ctr = 0;
   }

   /*
    * Undifference and scale each scanline of the disassembled MCU row
    * separately.  We do not process dummy samples at the end of a scanline
    * or dummy rows at the end of the image.
    */
   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
     compptr = cinfo->cur_comp_info[ci];
     compi = compptr->component_index;
     for (row = 0, prev_row = compptr->v_samp_factor - 1;
          row < (cinfo->input_iMCU_row == last_iMCU_row ?
                 compptr->last_row_height : compptr->v_samp_factor);
          prev_row = row, row++) {
       (*losslessd->predict_undifference[compi])
         (cinfo, compi, diff->diff_buf[compi][row],
           diff->undiff_buf[compi][prev_row], diff->undiff_buf[compi][row],
           compptr->width_in_blocks);
       (*losslessd->scaler_scale) (cinfo, diff->undiff_buf[compi][row],
                                   output_buf[compi][row],
                                   compptr->width_in_blocks);
     }
   }

   /* Completed the iMCU row, advance counters for next one.
    *
    * NB: output_data will increment output_iMCU_row.
    * This counter is not needed for the single-pass case
    * or the input side of the multi-pass case.
    */
   if (++(cinfo->input_iMCU_row) < cinfo->total_iMCU_rows) {
     start_iMCU_row(cinfo);
     return JPEG_ROW_COMPLETED;
   }
   /* Completed the scan */
   (*cinfo->inputctl->finish_input_pass) (cinfo);
   return JPEG_SCAN_COMPLETED;
 }


 /*
  * Dummy consume-input routine for single-pass operation.
  */

 METHODDEF(int)
 dummy_consume_data(j_decompress_ptr cinfo)
 {
   return JPEG_SUSPENDED;        /* Always indicate nothing was done */
 }


 #ifdef D_MULTISCAN_FILES_SUPPORTED

 /*
  * Consume input data and store it in the full-image sample buffer.
  * We read as much as one fully interleaved MCU row ("iMCU" row) per call,
  * ie, v_samp_factor rows for each component in the scan.
  * Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
  */

 METHODDEF(int)
 consume_data(j_decompress_ptr cinfo)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
   int ci, compi;
   _JSAMPARRAY buffer[MAX_COMPS_IN_SCAN];
   jpeg_component_info *compptr;

   /* Align the virtual buffers for the components used in this scan. */
   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
     compptr = cinfo->cur_comp_info[ci];
     compi = compptr->component_index;
     buffer[compi] = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
       ((j_common_ptr)cinfo, diff->whole_image[compi],
        cinfo->input_iMCU_row * compptr->v_samp_factor,
        (JDIMENSION)compptr->v_samp_factor, TRUE);
   }

   return decompress_data(cinfo, buffer);
 }


 /*
  * Output some data from the full-image sample buffer in the multi-pass case.
  * Always attempts to emit one fully interleaved MCU row ("iMCU" row).
  * Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
  *
  * NB: output_buf contains a plane for each component in image.
  */

 METHODDEF(int)
 output_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
   JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
   int ci, samp_rows, row;
   _JSAMPARRAY buffer;
   jpeg_component_info *compptr;

   /* Force some input to be done if we are getting ahead of the input. */
   while (cinfo->input_scan_number < cinfo->output_scan_number ||
          (cinfo->input_scan_number == cinfo->output_scan_number &&
           cinfo->input_iMCU_row <= cinfo->output_iMCU_row)) {
     if ((*cinfo->inputctl->consume_input) (cinfo) == JPEG_SUSPENDED)
       return JPEG_SUSPENDED;
   }

   /* OK, output from the virtual arrays. */
   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
        ci++, compptr++) {
     /* Align the virtual buffer for this component. */
     buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
       ((j_common_ptr)cinfo, diff->whole_image[ci],
        cinfo->output_iMCU_row * compptr->v_samp_factor,
        (JDIMENSION)compptr->v_samp_factor, FALSE);

     if (cinfo->output_iMCU_row < last_iMCU_row)
       samp_rows = compptr->v_samp_factor;
     else {
       /* NB: can't use last_row_height here; it is input-side-dependent! */
       samp_rows = (int)(compptr->height_in_blocks % compptr->v_samp_factor);
       if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
     }

     for (row = 0; row < samp_rows; row++) {
       memcpy(output_buf[ci][row], buffer[row],
              compptr->width_in_blocks * sizeof(_JSAMPLE));
     }
   }

   if (++(cinfo->output_iMCU_row) < cinfo->total_iMCU_rows)
     return JPEG_ROW_COMPLETED;
   return JPEG_SCAN_COMPLETED;
 }

 #endif /* D_MULTISCAN_FILES_SUPPORTED */


 /*
  * Initialize difference buffer controller.
  */

 GLOBAL(void)
 _jinit_d_diff_controller(j_decompress_ptr cinfo, boolean need_full_buffer)
 {
   my_diff_ptr diff;
   int ci;
   jpeg_component_info *compptr;

   diff = (my_diff_ptr)
     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
                                 sizeof(my_diff_controller));
   cinfo->coef = (struct jpeg_d_coef_controller *)diff;
   diff->pub.start_input_pass = start_input_pass;
   diff->pub.start_output_pass = start_output_pass;

   /* Create the [un]difference buffers. */
   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
        ci++, compptr++) {
     diff->diff_buf[ci] =
       ALLOC_DARRAY(JPOOL_IMAGE,
                    (JDIMENSION)jround_up((long)compptr->width_in_blocks,
                                          (long)compptr->h_samp_factor),
                    (JDIMENSION)compptr->v_samp_factor);
     diff->undiff_buf[ci] =
       ALLOC_DARRAY(JPOOL_IMAGE,
                    (JDIMENSION)jround_up((long)compptr->width_in_blocks,
                                          (long)compptr->h_samp_factor),
                    (JDIMENSION)compptr->v_samp_factor);
   }

   if (need_full_buffer) {
 #ifdef D_MULTISCAN_FILES_SUPPORTED
     /* Allocate a full-image virtual array for each component. */
     int access_rows;

     for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
          ci++, compptr++) {
       access_rows = compptr->v_samp_factor;
       diff->whole_image[ci] = (*cinfo->mem->request_virt_sarray)
         ((j_common_ptr)cinfo, JPOOL_IMAGE, FALSE,
          (JDIMENSION)jround_up((long)compptr->width_in_blocks,
                                (long)compptr->h_samp_factor),
          (JDIMENSION)jround_up((long)compptr->height_in_blocks,
                                (long)compptr->v_samp_factor),
          (JDIMENSION)access_rows);
     }
     diff->pub.consume_data = consume_data;
     diff->pub._decompress_data = output_data;
 #else
     ERREXIT(cinfo, JERR_NOT_COMPILED);
 #endif
   } else {
     diff->pub.consume_data = dummy_consume_data;
     diff->pub._decompress_data = decompress_data;
     diff->whole_image[0] = NULL; /* flag for no virtual arrays */
   }
 }

 #endif /* D_LOSSLESS_SUPPORTED */
	/*
	* jddiffct.c
	*
	* This file was part of the Independent JPEG Group's software:
	* Copyright (C) 1994-1997, Thomas G. Lane.
	* Lossless JPEG Modifications:
	* Copyright (C) 1999, Ken Murchison.
	* libjpeg-turbo Modifications:
	* Copyright (C) 2022, D. R. Commander.
	* For conditions of distribution and use, see the accompanying README.ijg
	* file.
	*
	* This file contains the [un]difference buffer controller for decompression.
	* This controller is the top level of the lossless JPEG decompressor proper.
	* The difference buffer lies between the entropy decoding and
	* prediction/undifferencing steps. The undifference buffer lies between the
	* prediction/undifferencing and scaling steps.
	*
	* In buffered-image mode, this controller is the interface between
	* input-oriented processing and output-oriented processing.
	*/

	#define JPEG_INTERNALS
	#include "jinclude.h"
	#include "jpeglib.h"
	#include "jlossls.h" /* Private declarations for lossless codec */


	#ifdef D_LOSSLESS_SUPPORTED

	/* Private buffer controller object */

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

	/* These variables keep track of the current location of the input side. */
	/* cinfo->input_iMCU_row is also used for this. */
	JDIMENSION MCU_ctr; /* counts MCUs processed in current row */
	unsigned int restart_rows_to_go; /* MCU rows left in this restart
	interval */
	unsigned int MCU_vert_offset; /* counts MCU rows within iMCU row */
	unsigned int MCU_rows_per_iMCU_row; /* number of such rows needed */

	/* The output side's location is represented by cinfo->output_iMCU_row. */

	JDIFFARRAY diff_buf[MAX_COMPONENTS]; /* iMCU row of differences */
	JDIFFARRAY undiff_buf[MAX_COMPONENTS]; /* iMCU row of undiff'd samples */

	#ifdef D_MULTISCAN_FILES_SUPPORTED
	/* In multi-pass modes, we need a virtual sample array for each component. */
	jvirt_sarray_ptr whole_image[MAX_COMPONENTS];
	#endif
	} my_diff_controller;

	typedef my_diff_controller *my_diff_ptr;

	/* Forward declarations */
	METHODDEF(int) decompress_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf);
	#ifdef D_MULTISCAN_FILES_SUPPORTED
	METHODDEF(int) output_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf);
	#endif


	LOCAL(void)
	start_iMCU_row(j_decompress_ptr cinfo)
	/* Reset within-iMCU-row counters for a new row (input side) */
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

	/* In an interleaved scan, an MCU row is the same as an iMCU row.
	* In a noninterleaved scan, an iMCU row has v_samp_factor MCU rows.
	* But at the bottom of the image, process only what's left.
	*/
	if (cinfo->comps_in_scan > 1) {
	diff->MCU_rows_per_iMCU_row = 1;
	} else {
	if (cinfo->input_iMCU_row < (cinfo->total_iMCU_rows-1))
	diff->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->v_samp_factor;
	else
	diff->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->last_row_height;
	}

	diff->MCU_ctr = 0;
	diff->MCU_vert_offset = 0;
	}


	/*
	* Initialize for an input processing pass.
	*/

	METHODDEF(void)
	start_input_pass(j_decompress_ptr cinfo)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

	/* Because it is hitching a ride on the jpeg_inverse_dct struct,
	* start_pass_lossless() will be called at the start of the output pass.
	* This ensures that it will be called at the start of the input pass as
	* well.
	*/
	(*cinfo->idct->start_pass) (cinfo);

	/* Check that the restart interval is an integer multiple of the number
	* of MCUs in an MCU row.
	*/
	if (cinfo->restart_interval % cinfo->MCUs_per_row != 0)
	ERREXIT2(cinfo, JERR_BAD_RESTART,
	cinfo->restart_interval, cinfo->MCUs_per_row);

	/* Initialize restart counter */
	diff->restart_rows_to_go = cinfo->restart_interval / cinfo->MCUs_per_row;

	cinfo->input_iMCU_row = 0;
	start_iMCU_row(cinfo);
	}


	/*
	* Check for a restart marker & resynchronize decoder, undifferencer.
	* Returns FALSE if must suspend.
	*/

	METHODDEF(boolean)
	process_restart(j_decompress_ptr cinfo)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

	if (!(*cinfo->entropy->process_restart) (cinfo))
	return FALSE;

	(*cinfo->idct->start_pass) (cinfo);

	/* Reset restart counter */
	diff->restart_rows_to_go = cinfo->restart_interval / cinfo->MCUs_per_row;

	return TRUE;
	}


	/*
	* Initialize for an output processing pass.
	*/

	METHODDEF(void)
	start_output_pass(j_decompress_ptr cinfo)
	{
	cinfo->output_iMCU_row = 0;
	}


	/*
	* Decompress and return some data in the supplied buffer.
	* Always attempts to emit one fully interleaved MCU row ("iMCU" row).
	* Input and output must run in lockstep since we have only a one-MCU buffer.
	* Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
	*
	* NB: output_buf contains a plane for each component in image,
	* which we index according to the component's SOF position.
	*/

	METHODDEF(int)
	decompress_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
	lossless_decomp_ptr losslessd = (lossless_decomp_ptr)cinfo->idct;
	JDIMENSION MCU_col_num; /* index of current MCU within row */
	JDIMENSION MCU_count; /* number of MCUs decoded */
	JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
	int ci, compi, row, prev_row;
	unsigned int yoffset;
	jpeg_component_info *compptr;

	/* Loop to process as much as one whole iMCU row */
	for (yoffset = diff->MCU_vert_offset; yoffset < diff->MCU_rows_per_iMCU_row;
	yoffset++) {

	/* Process restart marker if needed; may have to suspend */
	if (cinfo->restart_interval) {
	if (diff->restart_rows_to_go == 0)
	if (!process_restart(cinfo))
	return JPEG_SUSPENDED;
	}

	MCU_col_num = diff->MCU_ctr;
	/* Try to fetch an MCU row (or remaining portion of suspended MCU row). */
	MCU_count =
	(*cinfo->entropy->decode_mcus) (cinfo,
	diff->diff_buf, yoffset, MCU_col_num,
	cinfo->MCUs_per_row - MCU_col_num);
	if (MCU_count != cinfo->MCUs_per_row - MCU_col_num) {
	/* Suspension forced; update state counters and exit */
	diff->MCU_vert_offset = yoffset;
	diff->MCU_ctr += MCU_count;
	return JPEG_SUSPENDED;
	}

	/* Account for restart interval (no-op if not using restarts) */
	if (cinfo->restart_interval)
	diff->restart_rows_to_go--;

	/* Completed an MCU row, but perhaps not an iMCU row */
	diff->MCU_ctr = 0;
	}

	/*
	* Undifference and scale each scanline of the disassembled MCU row
	* separately. We do not process dummy samples at the end of a scanline
	* or dummy rows at the end of the image.
	*/
	for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
	compptr = cinfo->cur_comp_info[ci];
	compi = compptr->component_index;
	for (row = 0, prev_row = compptr->v_samp_factor - 1;
	row < (cinfo->input_iMCU_row == last_iMCU_row ?
	compptr->last_row_height : compptr->v_samp_factor);
	prev_row = row, row++) {
	(*losslessd->predict_undifference[compi])
	(cinfo, compi, diff->diff_buf[compi][row],
	diff->undiff_buf[compi][prev_row], diff->undiff_buf[compi][row],
	compptr->width_in_blocks);
	(*losslessd->scaler_scale) (cinfo, diff->undiff_buf[compi][row],
	output_buf[compi][row],
	compptr->width_in_blocks);
	}
	}

	/* Completed the iMCU row, advance counters for next one.
	*
	* NB: output_data will increment output_iMCU_row.
	* This counter is not needed for the single-pass case
	* or the input side of the multi-pass case.
	*/
	if (++(cinfo->input_iMCU_row) < cinfo->total_iMCU_rows) {
	start_iMCU_row(cinfo);
	return JPEG_ROW_COMPLETED;
	}
	/* Completed the scan */
	(*cinfo->inputctl->finish_input_pass) (cinfo);
	return JPEG_SCAN_COMPLETED;
	}


	/*
	* Dummy consume-input routine for single-pass operation.
	*/

	METHODDEF(int)
	dummy_consume_data(j_decompress_ptr cinfo)
	{
	return JPEG_SUSPENDED; /* Always indicate nothing was done */
	}


	#ifdef D_MULTISCAN_FILES_SUPPORTED

	/*
	* Consume input data and store it in the full-image sample buffer.
	* We read as much as one fully interleaved MCU row ("iMCU" row) per call,
	* ie, v_samp_factor rows for each component in the scan.
	* Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
	*/

	METHODDEF(int)
	consume_data(j_decompress_ptr cinfo)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
	int ci, compi;
	_JSAMPARRAY buffer[MAX_COMPS_IN_SCAN];
	jpeg_component_info *compptr;

	/* Align the virtual buffers for the components used in this scan. */
	for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
	compptr = cinfo->cur_comp_info[ci];
	compi = compptr->component_index;
	buffer[compi] = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
	((j_common_ptr)cinfo, diff->whole_image[compi],
	cinfo->input_iMCU_row * compptr->v_samp_factor,
	(JDIMENSION)compptr->v_samp_factor, TRUE);
	}

	return decompress_data(cinfo, buffer);
	}


	/*
	* Output some data from the full-image sample buffer in the multi-pass case.
	* Always attempts to emit one fully interleaved MCU row ("iMCU" row).
	* Return value is JPEG_ROW_COMPLETED, JPEG_SCAN_COMPLETED, or JPEG_SUSPENDED.
	*
	* NB: output_buf contains a plane for each component in image.
	*/

	METHODDEF(int)
	output_data(j_decompress_ptr cinfo, _JSAMPIMAGE output_buf)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
	JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
	int ci, samp_rows, row;
	_JSAMPARRAY buffer;
	jpeg_component_info *compptr;

	/* Force some input to be done if we are getting ahead of the input. */
	while (cinfo->input_scan_number < cinfo->output_scan_number \|\|
	(cinfo->input_scan_number == cinfo->output_scan_number &&
	cinfo->input_iMCU_row <= cinfo->output_iMCU_row)) {
	if ((*cinfo->inputctl->consume_input) (cinfo) == JPEG_SUSPENDED)
	return JPEG_SUSPENDED;
	}

	/* OK, output from the virtual arrays. */
	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	ci++, compptr++) {
	/* Align the virtual buffer for this component. */
	buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
	((j_common_ptr)cinfo, diff->whole_image[ci],
	cinfo->output_iMCU_row * compptr->v_samp_factor,
	(JDIMENSION)compptr->v_samp_factor, FALSE);

	if (cinfo->output_iMCU_row < last_iMCU_row)
	samp_rows = compptr->v_samp_factor;
	else {
	/* NB: can't use last_row_height here; it is input-side-dependent! */
	samp_rows = (int)(compptr->height_in_blocks % compptr->v_samp_factor);
	if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
	}

	for (row = 0; row < samp_rows; row++) {
	memcpy(output_buf[ci][row], buffer[row],
	compptr->width_in_blocks * sizeof(_JSAMPLE));
	}
	}

	if (++(cinfo->output_iMCU_row) < cinfo->total_iMCU_rows)
	return JPEG_ROW_COMPLETED;
	return JPEG_SCAN_COMPLETED;
	}

	#endif /* D_MULTISCAN_FILES_SUPPORTED */


	/*
	* Initialize difference buffer controller.
	*/

	GLOBAL(void)
	_jinit_d_diff_controller(j_decompress_ptr cinfo, boolean need_full_buffer)
	{
	my_diff_ptr diff;
	int ci;
	jpeg_component_info *compptr;

	diff = (my_diff_ptr)
	(*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
	sizeof(my_diff_controller));
	cinfo->coef = (struct jpeg_d_coef_controller *)diff;
	diff->pub.start_input_pass = start_input_pass;
	diff->pub.start_output_pass = start_output_pass;

	/* Create the [un]difference buffers. */
	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	ci++, compptr++) {
	diff->diff_buf[ci] =
	ALLOC_DARRAY(JPOOL_IMAGE,
	(JDIMENSION)jround_up((long)compptr->width_in_blocks,
	(long)compptr->h_samp_factor),
	(JDIMENSION)compptr->v_samp_factor);
	diff->undiff_buf[ci] =
	ALLOC_DARRAY(JPOOL_IMAGE,
	(JDIMENSION)jround_up((long)compptr->width_in_blocks,
	(long)compptr->h_samp_factor),
	(JDIMENSION)compptr->v_samp_factor);
	}

	if (need_full_buffer) {
	#ifdef D_MULTISCAN_FILES_SUPPORTED
	/* Allocate a full-image virtual array for each component. */
	int access_rows;

	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	ci++, compptr++) {
	access_rows = compptr->v_samp_factor;
	diff->whole_image[ci] = (*cinfo->mem->request_virt_sarray)
	((j_common_ptr)cinfo, JPOOL_IMAGE, FALSE,
	(JDIMENSION)jround_up((long)compptr->width_in_blocks,
	(long)compptr->h_samp_factor),
	(JDIMENSION)jround_up((long)compptr->height_in_blocks,
	(long)compptr->v_samp_factor),
	(JDIMENSION)access_rows);
	}
	diff->pub.consume_data = consume_data;
	diff->pub._decompress_data = output_data;
	#else
	ERREXIT(cinfo, JERR_NOT_COMPILED);
	#endif
	} else {
	diff->pub.consume_data = dummy_consume_data;
	diff->pub._decompress_data = decompress_data;
	diff->whole_image[0] = NULL; /* flag for no virtual arrays */
	}
	}

	#endif /* D_LOSSLESS_SUPPORTED */