jdcoefct.c

/*
 * jdcoefct.c
 *
 * Copyright (C) 1994, 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.
 */

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


/* Private buffer controller object */

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

  JDIMENSION MCU_col_num;	/* saves next MCU column to process */
  JDIMENSION MCU_row_num;	/* keep track of MCU row # within image */

  /* In single-pass modes without block smoothing, it's sufficient to buffer
   * just one MCU (although this may prove a bit slow in practice).
   * We allocate a workspace of 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.
   */
  JBLOCKROW MCU_buffer[MAX_BLOCKS_IN_MCU];

  /* In multi-pass modes, we need a virtual block array for each component. */
  jvirt_barray_ptr whole_image[MAX_COMPONENTS];
} my_coef_controller;

typedef my_coef_controller * my_coef_ptr;


/* Forward declarations */
METHODDEF boolean decompress_data
	JPP((j_decompress_ptr cinfo, JSAMPIMAGE output_buf));
#ifdef D_MULTISCAN_FILES_SUPPORTED
METHODDEF boolean decompress_read
	JPP((j_decompress_ptr cinfo, JSAMPIMAGE output_buf));
METHODDEF boolean decompress_output
	JPP((j_decompress_ptr cinfo, JSAMPIMAGE output_buf));
#endif


/*
 * Initialize for a processing pass.
 */

METHODDEF void
start_pass_coef (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
{
  my_coef_ptr coef = (my_coef_ptr) cinfo->coef;

  coef->MCU_col_num = 0;
  coef->MCU_row_num = 0;

  switch (pass_mode) {
  case JBUF_PASS_THRU:
    if (coef->whole_image[0] != NULL)