jdcoefct.c

这是从一款商业嵌入式浏览器中节选出来的代码

    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.
 */

/*
 * Determine whether block smoothing is applicable and safe.
 */

LOCAL boolean
smoothing_ok (j_decompress_ptr cinfo)
{
  boolean smoothing_useful = FALSE;
  int ci, coefi;
  jpeg_component_info *compptr;
  JQUANT_TBL * qtable;
  int * coef_bits;

  if (! cinfo->progressive_mode || cinfo->coef_bits == NULL)
    return FALSE;
  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. */
    for (coefi = 0; coefi <= 5; coefi++) {
      if (qtable->quantval[coefi] == 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++) {
      if (coef_bits[coefi] != 0)
	smoothing_useful = TRUE;
    }
  }

  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;
  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 = cinfo->coef_bits[ci];
    quanttbl = compptr->quant_table;
    Q00 = quanttbl->quantval[0];
    Q01 = quanttbl->quantval[1];
    Q10 = quanttbl->quantval[2];
    Q20 = quanttbl->quantval[3];
    Q11 = quanttbl->quantval[4];
    Q02 = quanttbl->quantval[5];
    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;
  coef->pub.start_input_pass = start_input_pass;
  coef->pub.start_output_pass = start_output_pass;

  /* 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 */
  }
}