www.pudn.com > imgport.rar > jdcoefct.c, change:2008-11-05,size:26095b


/* 
 * jdcoefct.c 
 * 
 * Copyright (C) 1994-1997, 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 the coefficient buffer controller for decompression. 
 * This controller is the top level of the JPEG decompressor proper. 
 * The coefficient buffer lies between entropy decoding and inverse-DCT steps. 
 * 
 * In buffered-image mode, this controller is the interface between 
 * input-oriented processing and output-oriented processing. 
 * Also, the input side (only) is used when reading a file for transcoding. 
 */ 
 
#define JPEG_INTERNALS 
#include "jinclude.h" 
#include "jpeglib.h" 
 
/* Block smoothing is only applicable for progressive JPEG, so: */ 
#ifndef D_PROGRESSIVE_SUPPORTED 
#undef BLOCK_SMOOTHING_SUPPORTED 
#endif 
 
/* 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 */ 
  int MCU_vert_offset;		/* counts MCU rows within iMCU row */ 
  int MCU_rows_per_iMCU_row;	/* number of such rows needed */ 
 
  /* The output side's location is represented by cinfo->output_iMCU_row. */ 
 
  /* In single-pass modes, it's sufficient to buffer just one MCU. 
   * We allocate a workspace of D_MAX_BLOCKS_IN_MCU coefficient blocks, 
   * and let the entropy decoder write into that workspace each time. 
   * (On 80x86, the workspace is FAR even though it's not really very big; 
   * this is to keep the module interfaces unchanged when a large coefficient 
   * buffer is necessary.) 
   * In multi-pass modes, this array points to the current MCU's blocks 
   * within the virtual arrays; it is used only by the input side. 
   */ 
  JBLOCKROW MCU_buffer[D_MAX_BLOCKS_IN_MCU]; 
 
#ifdef D_MULTISCAN_FILES_SUPPORTED 
  /* In multi-pass modes, we need a virtual block array for each component. */ 
  jvirt_barray_ptr whole_image[MAX_COMPONENTS]; 
#endif 
 
#ifdef BLOCK_SMOOTHING_SUPPORTED 
  /* When doing block smoothing, we latch coefficient Al values here */ 
  int * coef_bits_latch; 
#define SAVED_COEFS  6		/* we save coef_bits[0..5] */ 
#endif 
} my_coef_controller; 
 
typedef my_coef_controller * my_coef_ptr; 
 
/* Forward declarations */ 
METHODDEF(int) decompress_onepass 
	JPP((j_decompress_ptr cinfo, JSAMPIMAGE output_buf)); 
#ifdef D_MULTISCAN_FILES_SUPPORTED 
METHODDEF(int) decompress_data 
	JPP((j_decompress_ptr cinfo, JSAMPIMAGE output_buf)); 
#endif 
#ifdef BLOCK_SMOOTHING_SUPPORTED 
LOCAL(boolean) smoothing_ok JPP((j_decompress_ptr cinfo)); 
METHODDEF(int) decompress_smooth_data 
	JPP((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_coef_ptr coef = (my_coef_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) { 
    coef->MCU_rows_per_iMCU_row = 1; 
  } else { 
    if (cinfo->input_iMCU_row < (cinfo->total_iMCU_rows-1)) 
      coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->v_samp_factor; 
    else 
      coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->last_row_height; 
  } 
 
  coef->MCU_ctr = 0; 
  coef->MCU_vert_offset = 0; 
} 
 
 
/* 
 * Initialize for an input processing pass. 
 */ 
 
METHODDEF(void) 
//#if defined(__VISAGECPP__) 
start_input_pass2 (j_decompress_ptr cinfo) 
//#else 
//start_input_pass (j_decompress_ptr cinfo) 
//#endif 
{ 
  cinfo->input_iMCU_row = 0; 
  start_iMCU_row(cinfo); 
} 
 
/* 
 * Initialize for an output processing pass. 
 */ 
 
METHODDEF(void) 
start_output_pass (j_decompress_ptr cinfo) 
{ 
#ifdef BLOCK_SMOOTHING_SUPPORTED 
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef; 
 
  /* If multipass, check to see whether to use block smoothing on this pass */ 
  if (coef->pub.coef_arrays != NULL) { 
    if (cinfo->do_block_smoothing && smoothing_ok(cinfo)) 
      coef->pub.decompress_data = decompress_smooth_data; 
    else 
      coef->pub.decompress_data = decompress_data; 
  } 
#endif 
  cinfo->output_iMCU_row = 0; 
} 
 
 
/* 
 * Decompress and return some data in the single-pass case. 
 * 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_onepass (j_decompress_ptr cinfo, JSAMPIMAGE output_buf) 
{ 
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef; 
  JDIMENSION MCU_col_num;	/* index of current MCU within row */ 
  JDIMENSION last_MCU_col = cinfo->MCUs_per_row - 1; 
  JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1; 
  int blkn, ci, xindex, yindex, yoffset, useful_width; 
  JSAMPARRAY output_ptr; 
  JDIMENSION start_col, output_col; 
  jpeg_component_info *compptr; 
  inverse_DCT_method_ptr inverse_DCT; 
 
  /* Loop to process as much as one whole iMCU row */ 
  for (yoffset = coef->MCU_vert_offset; yoffset < coef->MCU_rows_per_iMCU_row; 
       yoffset++) { 
    for (MCU_col_num = coef->MCU_ctr; MCU_col_num <= last_MCU_col; 
	 MCU_col_num++) { 
      /* Try to fetch an MCU.  Entropy decoder expects buffer to be zeroed. */ 
      jzero_far((void FAR *) coef->MCU_buffer[0], 
		(size_t) (cinfo->blocks_in_MCU * SIZEOF(JBLOCK))); 
      if (! (*cinfo->entropy->decode_mcu) (cinfo, coef->MCU_buffer)) { 
	/* Suspension forced; update state counters and exit */ 
	coef->MCU_vert_offset = yoffset; 
	coef->MCU_ctr = MCU_col_num; 
	return JPEG_SUSPENDED; 
      } 
      /* Determine where data should go in output_buf and do the IDCT thing. 
       * We skip dummy blocks at the right and bottom edges (but blkn gets 
       * incremented past them!).  Note the inner loop relies on having 
       * allocated the MCU_buffer[] blocks sequentially. 
       */ 
      blkn = 0;			/* index of current DCT block within MCU */ 
      for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 
	compptr = cinfo->cur_comp_info[ci]; 
	/* Don't bother to IDCT an uninteresting component. */ 
	if (! compptr->component_needed) { 
	  blkn += compptr->MCU_blocks; 
	  continue; 
	} 
	inverse_DCT = cinfo->idct->inverse_DCT[compptr->component_index]; 
	useful_width = (MCU_col_num < last_MCU_col) ? compptr->MCU_width 
						    : compptr->last_col_width; 
	output_ptr = output_buf[compptr->component_index] + 
	  yoffset * compptr->DCT_scaled_size; 
	start_col = MCU_col_num * compptr->MCU_sample_width; 
	for (yindex = 0; yindex < compptr->MCU_height; yindex++) { 
	  if (cinfo->input_iMCU_row < last_iMCU_row || 
	      yoffset+yindex < compptr->last_row_height) { 
	    output_col = start_col; 
	    for (xindex = 0; xindex < useful_width; xindex++) { 
	      (*inverse_DCT) (cinfo, compptr, 
			      (JCOEFPTR) coef->MCU_buffer[blkn+xindex], 
			      output_ptr, output_col); 
	      output_col += compptr->DCT_scaled_size; 
	    } 
	  } 
	  blkn += compptr->MCU_width; 
	  output_ptr += compptr->DCT_scaled_size; 
	} 
      } 
    } 
    /* Completed an MCU row, but perhaps not an iMCU row */ 
    coef->MCU_ctr = 0; 
  } 
  /* Completed the iMCU row, advance counters for next one */ 
  cinfo->output_iMCU_row++; 
  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 coefficient buffer. 
 * We read as much as one fully interleaved MCU row ("iMCU" row) per call, 
 * ie, v_samp_factor block 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_coef_ptr coef = (my_coef_ptr) cinfo->coef; 
  JDIMENSION MCU_col_num;	/* index of current MCU within row */ 
  int blkn, ci, xindex, yindex, yoffset; 
  JDIMENSION start_col; 
  JBLOCKARRAY buffer[MAX_COMPS_IN_SCAN]; 
  JBLOCKROW buffer_ptr; 
  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]; 
    buffer[ci] = (*cinfo->mem->access_virt_barray) 
      ((j_common_ptr) cinfo, coef->whole_image[compptr->component_index], 
       cinfo->input_iMCU_row * compptr->v_samp_factor, 
       (JDIMENSION) compptr->v_samp_factor, TRUE); 
    /* Note: entropy decoder expects buffer to be zeroed, 
     * but this is handled automatically by the memory manager 
     * because we requested a pre-zeroed array. 
     */ 
  } 
 
  /* Loop to process one whole iMCU row */ 
  for (yoffset = coef->MCU_vert_offset; yoffset < coef->MCU_rows_per_iMCU_row; 
       yoffset++) { 
    for (MCU_col_num = coef->MCU_ctr; MCU_col_num < cinfo->MCUs_per_row; 
	 MCU_col_num++) { 
      /* Construct list of pointers to DCT blocks belonging to this MCU */ 
      blkn = 0;			/* index of current DCT block within MCU */ 
      for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 
	compptr = cinfo->cur_comp_info[ci]; 
	start_col = MCU_col_num * compptr->MCU_width; 
	for (yindex = 0; yindex < compptr->MCU_height; yindex++) { 
	  buffer_ptr = buffer[ci][yindex+yoffset] + start_col; 
	  for (xindex = 0; xindex < compptr->MCU_width; xindex++) { 
	    coef->MCU_buffer[blkn++] = buffer_ptr++; 
	  } 
	} 
      } 
      /* Try to fetch the MCU. */ 
      if (! (*cinfo->entropy->decode_mcu) (cinfo, coef->MCU_buffer)) { 
	/* Suspension forced; update state counters and exit */ 
	coef->MCU_vert_offset = yoffset; 
	coef->MCU_ctr = MCU_col_num; 
	return JPEG_SUSPENDED; 
      } 
    } 
    /* Completed an MCU row, but perhaps not an iMCU row */ 
    coef->MCU_ctr = 0; 
  } 
  /* Completed the iMCU row, advance counters for next one */ 
  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; 
} 
 
 
/* 
 * Decompress and return some data 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) 
decompress_data (j_decompress_ptr cinfo, JSAMPIMAGE output_buf) 
{ 
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef; 
  JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1; 
  JDIMENSION block_num; 
  int ci, block_row, block_rows; 
  JBLOCKARRAY buffer; 
  JBLOCKROW buffer_ptr; 
  JSAMPARRAY output_ptr; 
  JDIMENSION output_col; 
  jpeg_component_info *compptr; 
  inverse_DCT_method_ptr inverse_DCT; 
 
  /* 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++) { 
    /* Don't bother to IDCT an uninteresting component. */ 
    if (! compptr->component_needed) 
      continue; 
    /* Align the virtual buffer for this component. */ 
    buffer = (*cinfo->mem->access_virt_barray) 
      ((j_common_ptr) cinfo, coef->whole_image[ci], 
       cinfo->output_iMCU_row * compptr->v_samp_factor, 
       (JDIMENSION) compptr->v_samp_factor, FALSE); 
    /* Count non-dummy DCT block rows in this iMCU row. */ 
    if (cinfo->output_iMCU_row < last_iMCU_row) 
      block_rows = compptr->v_samp_factor; 
    else { 
      /* NB: can't use last_row_height here; it is input-side-dependent! */ 
      block_rows = (int) (compptr->height_in_blocks % compptr->v_samp_factor); 
      if (block_rows == 0) block_rows = compptr->v_samp_factor; 
    } 
    inverse_DCT = cinfo->idct->inverse_DCT[ci]; 
    output_ptr = output_buf[ci]; 
    /* Loop over all DCT blocks to be processed. */ 
    for (block_row = 0; block_row < block_rows; block_row++) { 
      buffer_ptr = buffer[block_row]; 
      output_col = 0; 
      for (block_num = 0; block_num < compptr->width_in_blocks; block_num++) { 
	(*inverse_DCT) (cinfo, compptr, (JCOEFPTR) buffer_ptr, 
			output_ptr, output_col); 
	buffer_ptr++; 
	output_col += compptr->DCT_scaled_size; 
      } 
      output_ptr += compptr->DCT_scaled_size; 
    } 
  } 
 
  if (++(cinfo->output_iMCU_row) < cinfo->total_iMCU_rows) 
    return JPEG_ROW_COMPLETED; 
  return JPEG_SCAN_COMPLETED; 
} 
 
#endif /* D_MULTISCAN_FILES_SUPPORTED */ 
 
 
#ifdef BLOCK_SMOOTHING_SUPPORTED 
 
/* 
 * This code applies interblock smoothing as described by section K.8 
 * of the JPEG standard: the first 5 AC coefficients are estimated from 
 * the DC values of a DCT block and its 8 neighboring blocks. 
 * We apply smoothing only for progressive JPEG decoding, and only if 
 * the coefficients it can estimate are not yet known to full precision. 
 */ 
 
/* Natural-order array positions of the first 5 zigzag-order coefficients */ 
#define Q01_POS  1 
#define Q10_POS  8 
#define Q20_POS  16 
#define Q11_POS  9 
#define Q02_POS  2 
 
/* 
 * Determine whether block smoothing is applicable and safe. 
 * We also latch the current states of the coef_bits[] entries for the 
 * AC coefficients; otherwise, if the input side of the decompressor 
 * advances into a new scan, we might think the coefficients are known 
 * more accurately than they really are. 
 */ 
 
LOCAL(boolean) 
smoothing_ok (j_decompress_ptr cinfo) 
{ 
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef; 
  boolean smoothing_useful = FALSE; 
  int ci, coefi; 
  jpeg_component_info *compptr; 
  JQUANT_TBL * qtable; 
  int * coef_bits; 
  int * coef_bits_latch; 
 
  if (! cinfo->progressive_mode || cinfo->coef_bits == NULL) 
    return FALSE; 
 
  /* Allocate latch area if not already done */ 
  if (coef->coef_bits_latch == NULL) 
    coef->coef_bits_latch = (int *) 
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				  cinfo->num_components * 
				  (SAVED_COEFS * SIZEOF(int))); 
  coef_bits_latch = coef->coef_bits_latch; 
 
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 
       ci++, compptr++) { 
    /* All components' quantization values must already be latched. */ 
    if ((qtable = compptr->quant_table) == NULL) 
      return FALSE; 
    /* Verify DC & first 5 AC quantizers are nonzero to avoid zero-divide. */ 
    if (qtable->quantval[0] == 0 || 
	qtable->quantval[Q01_POS] == 0 || 
	qtable->quantval[Q10_POS] == 0 || 
	qtable->quantval[Q20_POS] == 0 || 
	qtable->quantval[Q11_POS] == 0 || 
	qtable->quantval[Q02_POS] == 0) 
      return FALSE; 
    /* DC values must be at least partly known for all components. */ 
    coef_bits = cinfo->coef_bits[ci]; 
    if (coef_bits[0] < 0) 
      return FALSE; 
    /* Block smoothing is helpful if some AC coefficients remain inaccurate. */ 
    for (coefi = 1; coefi <= 5; coefi++) { 
      coef_bits_latch[coefi] = coef_bits[coefi]; 
      if (coef_bits[coefi] != 0) 
	smoothing_useful = TRUE; 
    } 
    coef_bits_latch += SAVED_COEFS; 
  } 
 
  return smoothing_useful; 
} 
 
 
/* 
 * Variant of decompress_data for use when doing block smoothing. 
 */ 
 
METHODDEF(int) 
decompress_smooth_data (j_decompress_ptr cinfo, JSAMPIMAGE output_buf) 
{ 
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef; 
  JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1; 
  JDIMENSION block_num, last_block_column; 
  int ci, block_row, block_rows, access_rows; 
  JBLOCKARRAY buffer; 
  JBLOCKROW buffer_ptr, prev_block_row, next_block_row; 
  JSAMPARRAY output_ptr; 
  JDIMENSION output_col; 
  jpeg_component_info *compptr; 
  inverse_DCT_method_ptr inverse_DCT; 
  boolean first_row, last_row; 
  JBLOCK workspace; 
  int *coef_bits; 
  JQUANT_TBL *quanttbl; 
  JPEG_INT32 Q00,Q01,Q02,Q10,Q11,Q20, num; 
  int DC1,DC2,DC3,DC4,DC5,DC6,DC7,DC8,DC9; 
  int Al, pred; 
 
  /* Force some input to be done if we are getting ahead of the input. */ 
  while (cinfo->input_scan_number <= cinfo->output_scan_number && 
	 ! cinfo->inputctl->eoi_reached) { 
    if (cinfo->input_scan_number == cinfo->output_scan_number) { 
      /* If input is working on current scan, we ordinarily want it to 
       * have completed the current row.  But if input scan is DC, 
       * we want it to keep one row ahead so that next block row's DC 
       * values are up to date. 
       */ 
      JDIMENSION delta = (cinfo->Ss == 0) ? 1 : 0; 
      if (cinfo->input_iMCU_row > cinfo->output_iMCU_row+delta) 
	break; 
    } 
    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++) { 
    /* Don't bother to IDCT an uninteresting component. */ 
    if (! compptr->component_needed) 
      continue; 
    /* Count non-dummy DCT block rows in this iMCU row. */ 
    if (cinfo->output_iMCU_row < last_iMCU_row) { 
      block_rows = compptr->v_samp_factor; 
      access_rows = block_rows * 2; /* this and next iMCU row */ 
      last_row = FALSE; 
    } else { 
      /* NB: can't use last_row_height here; it is input-side-dependent! */ 
      block_rows = (int) (compptr->height_in_blocks % compptr->v_samp_factor); 
      if (block_rows == 0) block_rows = compptr->v_samp_factor; 
      access_rows = block_rows; /* this iMCU row only */ 
      last_row = TRUE; 
    } 
    /* Align the virtual buffer for this component. */ 
    if (cinfo->output_iMCU_row > 0) { 
      access_rows += compptr->v_samp_factor; /* prior iMCU row too */ 
      buffer = (*cinfo->mem->access_virt_barray) 
	((j_common_ptr) cinfo, coef->whole_image[ci], 
	 (cinfo->output_iMCU_row - 1) * compptr->v_samp_factor, 
	 (JDIMENSION) access_rows, FALSE); 
      buffer += compptr->v_samp_factor;	/* point to current iMCU row */ 
      first_row = FALSE; 
    } else { 
      buffer = (*cinfo->mem->access_virt_barray) 
	((j_common_ptr) cinfo, coef->whole_image[ci], 
	 (JDIMENSION) 0, (JDIMENSION) access_rows, FALSE); 
      first_row = TRUE; 
    } 
    /* Fetch component-dependent info */ 
    coef_bits = coef->coef_bits_latch + (ci * SAVED_COEFS); 
    quanttbl = compptr->quant_table; 
    Q00 = quanttbl->quantval[0]; 
    Q01 = quanttbl->quantval[Q01_POS]; 
    Q10 = quanttbl->quantval[Q10_POS]; 
    Q20 = quanttbl->quantval[Q20_POS]; 
    Q11 = quanttbl->quantval[Q11_POS]; 
    Q02 = quanttbl->quantval[Q02_POS]; 
    inverse_DCT = cinfo->idct->inverse_DCT[ci]; 
    output_ptr = output_buf[ci]; 
    /* Loop over all DCT blocks to be processed. */ 
    for (block_row = 0; block_row < block_rows; block_row++) { 
      buffer_ptr = buffer[block_row]; 
      if (first_row && block_row == 0) 
	prev_block_row = buffer_ptr; 
      else 
	prev_block_row = buffer[block_row-1]; 
      if (last_row && block_row == block_rows-1) 
	next_block_row = buffer_ptr; 
      else 
	next_block_row = buffer[block_row+1]; 
      /* We fetch the surrounding DC values using a sliding-register approach. 
       * Initialize all nine here so as to do the right thing on narrow pics. 
       */ 
      DC1 = DC2 = DC3 = (int) prev_block_row[0][0]; 
      DC4 = DC5 = DC6 = (int) buffer_ptr[0][0]; 
      DC7 = DC8 = DC9 = (int) next_block_row[0][0]; 
      output_col = 0; 
      last_block_column = compptr->width_in_blocks - 1; 
      for (block_num = 0; block_num <= last_block_column; block_num++) { 
	/* Fetch current DCT block into workspace so we can modify it. */ 
	jcopy_block_row(buffer_ptr, (JBLOCKROW) workspace, (JDIMENSION) 1); 
	/* Update DC values */ 
	if (block_num < last_block_column) { 
	  DC3 = (int) prev_block_row[1][0]; 
	  DC6 = (int) buffer_ptr[1][0]; 
	  DC9 = (int) next_block_row[1][0]; 
	} 
	/* Compute coefficient estimates per K.8. 
	 * An estimate is applied only if coefficient is still zero, 
	 * and is not known to be fully accurate. 
	 */ 
	/* AC01 */ 
	if ((Al=coef_bits[1]) != 0 && workspace[1] == 0) { 
	  num = 36 * Q00 * (DC4 - DC6); 
	  if (num >= 0) { 
	    pred = (int) (((Q01<<7) + num) / (Q01<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	  } else { 
	    pred = (int) (((Q01<<7) - num) / (Q01<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	    pred = -pred; 
	  } 
	  workspace[1] = (JCOEF) pred; 
	} 
	/* AC10 */ 
	if ((Al=coef_bits[2]) != 0 && workspace[8] == 0) { 
	  num = 36 * Q00 * (DC2 - DC8); 
	  if (num >= 0) { 
	    pred = (int) (((Q10<<7) + num) / (Q10<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	  } else { 
	    pred = (int) (((Q10<<7) - num) / (Q10<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	    pred = -pred; 
	  } 
	  workspace[8] = (JCOEF) pred; 
	} 
	/* AC20 */ 
	if ((Al=coef_bits[3]) != 0 && workspace[16] == 0) { 
	  num = 9 * Q00 * (DC2 + DC8 - 2*DC5); 
	  if (num >= 0) { 
	    pred = (int) (((Q20<<7) + num) / (Q20<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	  } else { 
	    pred = (int) (((Q20<<7) - num) / (Q20<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	    pred = -pred; 
	  } 
	  workspace[16] = (JCOEF) pred; 
	} 
	/* AC11 */ 
	if ((Al=coef_bits[4]) != 0 && workspace[9] == 0) { 
	  num = 5 * Q00 * (DC1 - DC3 - DC7 + DC9); 
	  if (num >= 0) { 
	    pred = (int) (((Q11<<7) + num) / (Q11<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	  } else { 
	    pred = (int) (((Q11<<7) - num) / (Q11<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	    pred = -pred; 
	  } 
	  workspace[9] = (JCOEF) pred; 
	} 
	/* AC02 */ 
	if ((Al=coef_bits[5]) != 0 && workspace[2] == 0) { 
	  num = 9 * Q00 * (DC4 + DC6 - 2*DC5); 
	  if (num >= 0) { 
	    pred = (int) (((Q02<<7) + num) / (Q02<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	  } else { 
	    pred = (int) (((Q02<<7) - num) / (Q02<<8)); 
	    if (Al > 0 && pred >= (1<<Al)) 
	      pred = (1<<Al)-1; 
	    pred = -pred; 
	  } 
	  workspace[2] = (JCOEF) pred; 
	} 
	/* OK, do the IDCT */ 
	(*inverse_DCT) (cinfo, compptr, (JCOEFPTR) workspace, 
			output_ptr, output_col); 
	/* Advance for next column */ 
	DC1 = DC2; DC2 = DC3; 
	DC4 = DC5; DC5 = DC6; 
	DC7 = DC8; DC8 = DC9; 
	buffer_ptr++, prev_block_row++, next_block_row++; 
	output_col += compptr->DCT_scaled_size; 
      } 
      output_ptr += compptr->DCT_scaled_size; 
    } 
  } 
 
  if (++(cinfo->output_iMCU_row) < cinfo->total_iMCU_rows) 
    return JPEG_ROW_COMPLETED; 
  return JPEG_SCAN_COMPLETED; 
} 
 
#endif /* BLOCK_SMOOTHING_SUPPORTED */ 
 
 
/* 
 * Initialize coefficient buffer controller. 
 */ 
 
GLOBAL(void) 
jinit_d_coef_controller (j_decompress_ptr cinfo, boolean need_full_buffer) 
{ 
  my_coef_ptr coef; 
 
  coef = (my_coef_ptr) 
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				SIZEOF(my_coef_controller)); 
  cinfo->coef = (struct jpeg_d_coef_controller *) coef; 
//#if defined(__VISAGECPP__) 
  coef->pub.start_input_pass = start_input_pass2; 
//#else 
//  coef->pub.start_input_pass = start_input_pass; 
//#endif 
 
  coef->pub.start_output_pass = start_output_pass; 
#ifdef BLOCK_SMOOTHING_SUPPORTED 
  coef->coef_bits_latch = NULL; 
#endif 
 
  /* Create the coefficient buffer. */ 
  if (need_full_buffer) { 
#ifdef D_MULTISCAN_FILES_SUPPORTED 
    /* Allocate a full-image virtual array for each component, */ 
    /* padded to a multiple of samp_factor DCT blocks in each direction. */ 
    /* Note we ask for a pre-zeroed array. */ 
    int ci, access_rows; 
    jpeg_component_info *compptr; 
 
    for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 
	 ci++, compptr++) { 
      access_rows = compptr->v_samp_factor; 
#ifdef BLOCK_SMOOTHING_SUPPORTED 
      /* If block smoothing could be used, need a bigger window */ 
      if (cinfo->progressive_mode) 
	access_rows *= 3; 
#endif 
      coef->whole_image[ci] = (*cinfo->mem->request_virt_barray) 
	((j_common_ptr) cinfo, JPOOL_IMAGE, TRUE, 
	 (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); 
    } 
    coef->pub.consume_data = consume_data; 
    coef->pub.decompress_data = decompress_data; 
    coef->pub.coef_arrays = coef->whole_image; /* link to virtual arrays */ 
#else 
    ERREXIT(cinfo, JERR_NOT_COMPILED); 
#endif 
  } else { 
    /* We only need a single-MCU buffer. */ 
    JBLOCKROW buffer; 
    int i; 
 
    buffer = (JBLOCKROW) 
      (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE, 
				  D_MAX_BLOCKS_IN_MCU * SIZEOF(JBLOCK)); 
    for (i = 0; i < D_MAX_BLOCKS_IN_MCU; i++) { 
      coef->MCU_buffer[i] = buffer + i; 
    } 
    coef->pub.consume_data = dummy_consume_data; 
    coef->pub.decompress_data = decompress_onepass; 
    coef->pub.coef_arrays = NULL; /* flag for no virtual arrays */ 
  } 
}