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

 /*
  * jcdiffct.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 difference buffer controller for compression.
  * This controller is the top level of the lossless JPEG compressor proper.
  * The difference buffer lies between the prediction/differencing and entropy
  * encoding steps.
  */

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


 #ifdef C_LOSSLESS_SUPPORTED

 /* We use a full-image sample buffer when doing Huffman optimization,
  * and also for writing multiple-scan JPEG files.  In all cases, the
  * full-image buffer is filled during the first pass, and the scaling,
  * prediction and differencing steps are run during subsequent passes.
  */
 #ifdef ENTROPY_OPT_SUPPORTED
 #define FULL_SAMP_BUFFER_SUPPORTED
 #else
 #ifdef C_MULTISCAN_FILES_SUPPORTED
 #define FULL_SAMP_BUFFER_SUPPORTED
 #endif
 #endif


 /* Private buffer controller object */

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

   JDIMENSION iMCU_row_num;      /* iMCU row # within image */
   JDIMENSION mcu_ctr;           /* counts MCUs processed in current row */
   int MCU_vert_offset;          /* counts MCU rows within iMCU row */
   int MCU_rows_per_iMCU_row;    /* number of such rows needed */

   _JSAMPROW cur_row[MAX_COMPONENTS];    /* row of point-transformed samples */
   _JSAMPROW prev_row[MAX_COMPONENTS];   /* previous row of Pt'd samples */
   JDIFFARRAY diff_buf[MAX_COMPONENTS];  /* iMCU row of differences */

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

 typedef my_diff_controller *my_diff_ptr;


 /* Forward declarations */
 METHODDEF(boolean) compress_data(j_compress_ptr cinfo, _JSAMPIMAGE input_buf);
 #ifdef FULL_SAMP_BUFFER_SUPPORTED
 METHODDEF(boolean) compress_first_pass(j_compress_ptr cinfo,
                                        _JSAMPIMAGE input_buf);
 METHODDEF(boolean) compress_output(j_compress_ptr cinfo,
                                    _JSAMPIMAGE input_buf);
 #endif


 LOCAL(void)
 start_iMCU_row(j_compress_ptr cinfo)
 /* Reset within-iMCU-row counters for a new row */
 {
   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 (diff->iMCU_row_num < (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 a processing pass.
  */

 METHODDEF(void)
 start_pass_diff(j_compress_ptr cinfo, J_BUF_MODE pass_mode)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

   /* Because it is hitching a ride on the jpeg_forward_dct struct,
    * start_pass_lossless() will be called at the start of the initial pass.
    * This ensures that it will be called at the start of the Huffman
    * optimization and output passes as well.
    */
   if (pass_mode == JBUF_CRANK_DEST)
     (*cinfo->fdct->start_pass) (cinfo);

   diff->iMCU_row_num = 0;
   start_iMCU_row(cinfo);

   switch (pass_mode) {
   case JBUF_PASS_THRU:
     if (diff->whole_image[0] != NULL)
       ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
     diff->pub._compress_data = compress_data;
     break;
 #ifdef FULL_SAMP_BUFFER_SUPPORTED
   case JBUF_SAVE_AND_PASS:
     if (diff->whole_image[0] == NULL)
       ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
     diff->pub._compress_data = compress_first_pass;
     break;
   case JBUF_CRANK_DEST:
     if (diff->whole_image[0] == NULL)
       ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
     diff->pub._compress_data = compress_output;
     break;
 #endif
   default:
     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
     break;
   }
 }


 #define SWAP_ROWS(rowa, rowb) { \
   _JSAMPROW temp = rowa; \
   rowa = rowb;  rowb = temp; \
 }

 /*
  * Process some data in the single-pass case.
  * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
  * per call, ie, v_samp_factor rows for each component in the image.
  * Returns TRUE if the iMCU row is completed, FALSE if suspended.
  *
  * NB: input_buf contains a plane for each component in image,
  * which we index according to the component's SOF position.
  */

 METHODDEF(boolean)
 compress_data(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
   lossless_comp_ptr losslessc = (lossless_comp_ptr)cinfo->fdct;
   JDIMENSION MCU_col_num;       /* index of current MCU within row */
   JDIMENSION MCU_count;         /* number of MCUs encoded */
   JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
   int ci, compi, yoffset, samp_row, samp_rows, samps_across;
   jpeg_component_info *compptr;

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

     MCU_col_num = diff->mcu_ctr;

     /* Scale and predict each scanline of the MCU row separately.
      *
      * Note: We only do this if we are at the start of an MCU row, ie,
      * we don't want to reprocess a row suspended by the output.
      */
     if (MCU_col_num == 0) {
       for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
         compptr = cinfo->cur_comp_info[ci];
         compi = compptr->component_index;
         if (diff->iMCU_row_num < last_iMCU_row)
           samp_rows = compptr->v_samp_factor;
         else {
           /* NB: can't use last_row_height here, since may not be set! */
           samp_rows =
             (int)(compptr->height_in_blocks % compptr->v_samp_factor);
           if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
           else {
             /* Fill dummy difference rows at the bottom edge with zeros, which
              * will encode to the smallest amount of data.
              */
             for (samp_row = samp_rows; samp_row < compptr->v_samp_factor;
                  samp_row++)
               memset(diff->diff_buf[compi][samp_row], 0,
                      jround_up((long)compptr->width_in_blocks,
                                (long)compptr->h_samp_factor) * sizeof(JDIFF));
           }
         }
         samps_across = compptr->width_in_blocks;

         for (samp_row = 0; samp_row < samp_rows; samp_row++) {
           (*losslessc->scaler_scale) (cinfo,
                                       input_buf[compi][samp_row],
                                       diff->cur_row[compi],
                                       samps_across);
           (*losslessc->predict_difference[compi])
             (cinfo, compi, diff->cur_row[compi], diff->prev_row[compi],
              diff->diff_buf[compi][samp_row], samps_across);
           SWAP_ROWS(diff->cur_row[compi], diff->prev_row[compi]);
         }
       }
     }
     /* Try to write the MCU row (or remaining portion of suspended MCU row). */
     MCU_count =
       (*cinfo->entropy->encode_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_col_num;
       return FALSE;
     }
     /* Completed an MCU row, but perhaps not an iMCU row */
     diff->mcu_ctr = 0;
   }
   /* Completed the iMCU row, advance counters for next one */
   diff->iMCU_row_num++;
   start_iMCU_row(cinfo);
   return TRUE;
 }


 #ifdef FULL_SAMP_BUFFER_SUPPORTED

 /*
  * Process some data in the first pass of a multi-pass case.
  * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
  * per call, ie, v_samp_factor rows for each component in the image.
  * This amount of data is read from the source buffer and saved into the
  * virtual arrays.
  *
  * We must also emit the data to the compressor.  This is conveniently
  * done by calling compress_output() after we've loaded the current strip
  * of the virtual arrays.
  *
  * NB: input_buf contains a plane for each component in image.  All components
  * are loaded into the virtual arrays in this pass.  However, it may be that
  * only a subset of the components are emitted to the compressor during
  * this first pass; be careful about looking at the scan-dependent variables
  * (MCU dimensions, etc).
  */

 METHODDEF(boolean)
 compress_first_pass(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
 {
   my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
   JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
   JDIMENSION samps_across;
   int ci, samp_row, samp_rows;
   _JSAMPARRAY buffer;
   jpeg_component_info *compptr;

   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],
        diff->iMCU_row_num * compptr->v_samp_factor,
        (JDIMENSION)compptr->v_samp_factor, TRUE);

     /* Count non-dummy sample rows in this iMCU row. */
     if (diff->iMCU_row_num < last_iMCU_row)
       samp_rows = compptr->v_samp_factor;
     else {
       /* NB: can't use last_row_height here, since may not be set! */
       samp_rows = (int)(compptr->height_in_blocks % compptr->v_samp_factor);
       if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
     }
     samps_across = compptr->width_in_blocks;

     /* Perform point transform scaling and prediction/differencing for all
      * non-dummy rows in this iMCU row.  Each call on these functions
      * processes a complete row of samples.
      */
     for (samp_row = 0; samp_row < samp_rows; samp_row++) {
       memcpy(buffer[samp_row], input_buf[ci][samp_row],
              samps_across * sizeof(_JSAMPLE));
     }
   }
   /* NB: compress_output will increment iMCU_row_num if successful.
    * A suspension return will result in redoing all the work above next time.
    */

   /* Emit data to the compressor, sharing code with subsequent passes */
   return compress_output(cinfo, input_buf);
 }


 /*
  * Process some data in subsequent passes of a multi-pass case.
  * We process the equivalent of one fully interleaved MCU row ("iMCU" row)
  * per call, ie, v_samp_factor rows for each component in the scan.
  * The data is obtained from the virtual arrays and fed to the compressor.
  * Returns TRUE if the iMCU row is completed, FALSE if suspended.
  *
  * NB: input_buf is ignored; it is likely to be a NULL pointer.
  */

 METHODDEF(boolean)
 compress_output(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
 {
   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.
    * NB: during first pass, this is safe only because the buffers will
    * already be aligned properly, so jmemmgr.c won't need to do any I/O.
    */
   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],
        diff->iMCU_row_num * compptr->v_samp_factor,
        (JDIMENSION)compptr->v_samp_factor, FALSE);
   }

   return compress_data(cinfo, buffer);
 }

 #endif /* FULL_SAMP_BUFFER_SUPPORTED */


 /*
  * Initialize difference buffer controller.
  */

 GLOBAL(void)
 _jinit_c_diff_controller(j_compress_ptr cinfo, boolean need_full_buffer)
 {
   my_diff_ptr diff;
   int ci, row;
   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_c_coef_controller *)diff;
   diff->pub.start_pass = start_pass_diff;

   /* Create the prediction row buffers. */
   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
        ci++, compptr++) {
     diff->cur_row[ci] = *(_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
       ((j_common_ptr)cinfo, JPOOL_IMAGE,
        (JDIMENSION)jround_up((long)compptr->width_in_blocks,
                              (long)compptr->h_samp_factor),
        (JDIMENSION)1);
     diff->prev_row[ci] = *(_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
       ((j_common_ptr)cinfo, JPOOL_IMAGE,
        (JDIMENSION)jround_up((long)compptr->width_in_blocks,
                              (long)compptr->h_samp_factor),
        (JDIMENSION)1);
   }

   /* Create the difference buffer. */
   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);
     /* Prefill difference rows with zeros.  We do this because only actual
      * data is placed in the buffers during prediction/differencing, leaving
      * any dummy differences at the right edge as zeros, which will encode
      * to the smallest amount of data.
      */
     for (row = 0; row < compptr->v_samp_factor; row++)
       memset(diff->diff_buf[ci][row], 0,
              jround_up((long)compptr->width_in_blocks,
                        (long)compptr->h_samp_factor) * sizeof(JDIFF));
   }

   /* Create the sample buffer. */
   if (need_full_buffer) {
 #ifdef FULL_SAMP_BUFFER_SUPPORTED
     /* Allocate a full-image virtual array for each component, */
     /* padded to a multiple of samp_factor differences in each direction. */
     for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
          ci++, compptr++) {
       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)compptr->v_samp_factor);
     }
 #else
     ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
 #endif
   } else
     diff->whole_image[0] = NULL; /* flag for no virtual arrays */
 }

 #endif /* C_LOSSLESS_SUPPORTED */
	/*
	* jcdiffct.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 difference buffer controller for compression.
	* This controller is the top level of the lossless JPEG compressor proper.
	* The difference buffer lies between the prediction/differencing and entropy
	* encoding steps.
	*/

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


	#ifdef C_LOSSLESS_SUPPORTED

	/* We use a full-image sample buffer when doing Huffman optimization,
	* and also for writing multiple-scan JPEG files. In all cases, the
	* full-image buffer is filled during the first pass, and the scaling,
	* prediction and differencing steps are run during subsequent passes.
	*/
	#ifdef ENTROPY_OPT_SUPPORTED
	#define FULL_SAMP_BUFFER_SUPPORTED
	#else
	#ifdef C_MULTISCAN_FILES_SUPPORTED
	#define FULL_SAMP_BUFFER_SUPPORTED
	#endif
	#endif


	/* Private buffer controller object */

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

	JDIMENSION iMCU_row_num; /* iMCU row # within image */
	JDIMENSION mcu_ctr; /* counts MCUs processed in current row */
	int MCU_vert_offset; /* counts MCU rows within iMCU row */
	int MCU_rows_per_iMCU_row; /* number of such rows needed */

	_JSAMPROW cur_row[MAX_COMPONENTS]; /* row of point-transformed samples */
	_JSAMPROW prev_row[MAX_COMPONENTS]; /* previous row of Pt'd samples */
	JDIFFARRAY diff_buf[MAX_COMPONENTS]; /* iMCU row of differences */

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

	typedef my_diff_controller *my_diff_ptr;


	/* Forward declarations */
	METHODDEF(boolean) compress_data(j_compress_ptr cinfo, _JSAMPIMAGE input_buf);
	#ifdef FULL_SAMP_BUFFER_SUPPORTED
	METHODDEF(boolean) compress_first_pass(j_compress_ptr cinfo,
	_JSAMPIMAGE input_buf);
	METHODDEF(boolean) compress_output(j_compress_ptr cinfo,
	_JSAMPIMAGE input_buf);
	#endif


	LOCAL(void)
	start_iMCU_row(j_compress_ptr cinfo)
	/* Reset within-iMCU-row counters for a new row */
	{
	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 (diff->iMCU_row_num < (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 a processing pass.
	*/

	METHODDEF(void)
	start_pass_diff(j_compress_ptr cinfo, J_BUF_MODE pass_mode)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;

	/* Because it is hitching a ride on the jpeg_forward_dct struct,
	* start_pass_lossless() will be called at the start of the initial pass.
	* This ensures that it will be called at the start of the Huffman
	* optimization and output passes as well.
	*/
	if (pass_mode == JBUF_CRANK_DEST)
	(*cinfo->fdct->start_pass) (cinfo);

	diff->iMCU_row_num = 0;
	start_iMCU_row(cinfo);

	switch (pass_mode) {
	case JBUF_PASS_THRU:
	if (diff->whole_image[0] != NULL)
	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
	diff->pub._compress_data = compress_data;
	break;
	#ifdef FULL_SAMP_BUFFER_SUPPORTED
	case JBUF_SAVE_AND_PASS:
	if (diff->whole_image[0] == NULL)
	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
	diff->pub._compress_data = compress_first_pass;
	break;
	case JBUF_CRANK_DEST:
	if (diff->whole_image[0] == NULL)
	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
	diff->pub._compress_data = compress_output;
	break;
	#endif
	default:
	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
	break;
	}
	}


	#define SWAP_ROWS(rowa, rowb) { \
	_JSAMPROW temp = rowa; \
	rowa = rowb; rowb = temp; \
	}

	/*
	* Process some data in the single-pass case.
	* We process the equivalent of one fully interleaved MCU row ("iMCU" row)
	* per call, ie, v_samp_factor rows for each component in the image.
	* Returns TRUE if the iMCU row is completed, FALSE if suspended.
	*
	* NB: input_buf contains a plane for each component in image,
	* which we index according to the component's SOF position.
	*/

	METHODDEF(boolean)
	compress_data(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
	lossless_comp_ptr losslessc = (lossless_comp_ptr)cinfo->fdct;
	JDIMENSION MCU_col_num; /* index of current MCU within row */
	JDIMENSION MCU_count; /* number of MCUs encoded */
	JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
	int ci, compi, yoffset, samp_row, samp_rows, samps_across;
	jpeg_component_info *compptr;

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

	MCU_col_num = diff->mcu_ctr;

	/* Scale and predict each scanline of the MCU row separately.
	*
	* Note: We only do this if we are at the start of an MCU row, ie,
	* we don't want to reprocess a row suspended by the output.
	*/
	if (MCU_col_num == 0) {
	for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
	compptr = cinfo->cur_comp_info[ci];
	compi = compptr->component_index;
	if (diff->iMCU_row_num < last_iMCU_row)
	samp_rows = compptr->v_samp_factor;
	else {
	/* NB: can't use last_row_height here, since may not be set! */
	samp_rows =
	(int)(compptr->height_in_blocks % compptr->v_samp_factor);
	if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
	else {
	/* Fill dummy difference rows at the bottom edge with zeros, which
	* will encode to the smallest amount of data.
	*/
	for (samp_row = samp_rows; samp_row < compptr->v_samp_factor;
	samp_row++)
	memset(diff->diff_buf[compi][samp_row], 0,
	jround_up((long)compptr->width_in_blocks,
	(long)compptr->h_samp_factor) * sizeof(JDIFF));
	}
	}
	samps_across = compptr->width_in_blocks;

	for (samp_row = 0; samp_row < samp_rows; samp_row++) {
	(*losslessc->scaler_scale) (cinfo,
	input_buf[compi][samp_row],
	diff->cur_row[compi],
	samps_across);
	(*losslessc->predict_difference[compi])
	(cinfo, compi, diff->cur_row[compi], diff->prev_row[compi],
	diff->diff_buf[compi][samp_row], samps_across);
	SWAP_ROWS(diff->cur_row[compi], diff->prev_row[compi]);
	}
	}
	}
	/* Try to write the MCU row (or remaining portion of suspended MCU row). */
	MCU_count =
	(*cinfo->entropy->encode_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_col_num;
	return FALSE;
	}
	/* Completed an MCU row, but perhaps not an iMCU row */
	diff->mcu_ctr = 0;
	}
	/* Completed the iMCU row, advance counters for next one */
	diff->iMCU_row_num++;
	start_iMCU_row(cinfo);
	return TRUE;
	}


	#ifdef FULL_SAMP_BUFFER_SUPPORTED

	/*
	* Process some data in the first pass of a multi-pass case.
	* We process the equivalent of one fully interleaved MCU row ("iMCU" row)
	* per call, ie, v_samp_factor rows for each component in the image.
	* This amount of data is read from the source buffer and saved into the
	* virtual arrays.
	*
	* We must also emit the data to the compressor. This is conveniently
	* done by calling compress_output() after we've loaded the current strip
	* of the virtual arrays.
	*
	* NB: input_buf contains a plane for each component in image. All components
	* are loaded into the virtual arrays in this pass. However, it may be that
	* only a subset of the components are emitted to the compressor during
	* this first pass; be careful about looking at the scan-dependent variables
	* (MCU dimensions, etc).
	*/

	METHODDEF(boolean)
	compress_first_pass(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
	{
	my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
	JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
	JDIMENSION samps_across;
	int ci, samp_row, samp_rows;
	_JSAMPARRAY buffer;
	jpeg_component_info *compptr;

	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],
	diff->iMCU_row_num * compptr->v_samp_factor,
	(JDIMENSION)compptr->v_samp_factor, TRUE);

	/* Count non-dummy sample rows in this iMCU row. */
	if (diff->iMCU_row_num < last_iMCU_row)
	samp_rows = compptr->v_samp_factor;
	else {
	/* NB: can't use last_row_height here, since may not be set! */
	samp_rows = (int)(compptr->height_in_blocks % compptr->v_samp_factor);
	if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
	}
	samps_across = compptr->width_in_blocks;

	/* Perform point transform scaling and prediction/differencing for all
	* non-dummy rows in this iMCU row. Each call on these functions
	* processes a complete row of samples.
	*/
	for (samp_row = 0; samp_row < samp_rows; samp_row++) {
	memcpy(buffer[samp_row], input_buf[ci][samp_row],
	samps_across * sizeof(_JSAMPLE));
	}
	}
	/* NB: compress_output will increment iMCU_row_num if successful.
	* A suspension return will result in redoing all the work above next time.
	*/

	/* Emit data to the compressor, sharing code with subsequent passes */
	return compress_output(cinfo, input_buf);
	}


	/*
	* Process some data in subsequent passes of a multi-pass case.
	* We process the equivalent of one fully interleaved MCU row ("iMCU" row)
	* per call, ie, v_samp_factor rows for each component in the scan.
	* The data is obtained from the virtual arrays and fed to the compressor.
	* Returns TRUE if the iMCU row is completed, FALSE if suspended.
	*
	* NB: input_buf is ignored; it is likely to be a NULL pointer.
	*/

	METHODDEF(boolean)
	compress_output(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
	{
	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.
	* NB: during first pass, this is safe only because the buffers will
	* already be aligned properly, so jmemmgr.c won't need to do any I/O.
	*/
	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],
	diff->iMCU_row_num * compptr->v_samp_factor,
	(JDIMENSION)compptr->v_samp_factor, FALSE);
	}

	return compress_data(cinfo, buffer);
	}

	#endif /* FULL_SAMP_BUFFER_SUPPORTED */


	/*
	* Initialize difference buffer controller.
	*/

	GLOBAL(void)
	_jinit_c_diff_controller(j_compress_ptr cinfo, boolean need_full_buffer)
	{
	my_diff_ptr diff;
	int ci, row;
	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_c_coef_controller *)diff;
	diff->pub.start_pass = start_pass_diff;

	/* Create the prediction row buffers. */
	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	ci++, compptr++) {
	diff->cur_row[ci] = (_JSAMPARRAY)(cinfo->mem->alloc_sarray)
	((j_common_ptr)cinfo, JPOOL_IMAGE,
	(JDIMENSION)jround_up((long)compptr->width_in_blocks,
	(long)compptr->h_samp_factor),
	(JDIMENSION)1);
	diff->prev_row[ci] = (_JSAMPARRAY)(cinfo->mem->alloc_sarray)
	((j_common_ptr)cinfo, JPOOL_IMAGE,
	(JDIMENSION)jround_up((long)compptr->width_in_blocks,
	(long)compptr->h_samp_factor),
	(JDIMENSION)1);
	}

	/* Create the difference buffer. */
	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);
	/* Prefill difference rows with zeros. We do this because only actual
	* data is placed in the buffers during prediction/differencing, leaving
	* any dummy differences at the right edge as zeros, which will encode
	* to the smallest amount of data.
	*/
	for (row = 0; row < compptr->v_samp_factor; row++)
	memset(diff->diff_buf[ci][row], 0,
	jround_up((long)compptr->width_in_blocks,
	(long)compptr->h_samp_factor) * sizeof(JDIFF));
	}

	/* Create the sample buffer. */
	if (need_full_buffer) {
	#ifdef FULL_SAMP_BUFFER_SUPPORTED
	/* Allocate a full-image virtual array for each component, */
	/* padded to a multiple of samp_factor differences in each direction. */
	for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
	ci++, compptr++) {
	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)compptr->v_samp_factor);
	}
	#else
	ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
	#endif
	} else
	diff->whole_image[0] = NULL; /* flag for no virtual arrays */
	}

	#endif /* C_LOSSLESS_SUPPORTED */