jddctmgr.c

PictureBrowser 是基于Altera 的DE2 开发板设计图像浏览器

/*
 * jddctmgr.c
 *
 * Copyright (C) 1994-1996, 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 inverse-DCT management logic.
 * This code selects a particular IDCT implementation to be used,
 * and it performs related housekeeping chores.  No code in this
file
 * is executed per IDCT step, only during output pass setup.
 *
 * Note that the IDCT routines are responsible for performing
coefficient
 * dequantization as well as the IDCT proper.  This module sets up
the
 * dequantization multiplier table needed by the IDCT routine.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h"                /* Private declarations for DCT subsystem */


/*
 * The decompressor input side (jdinput.c) saves away the
appropriate
 * quantization table for each component at the start of the first
scan
 * involving that component.  (This is necessary in order to
correctly
 * decode files that reuse Q-table slots.)
 * When we are ready to make an output pass, the saved Q-table is
converted
 * to a multiplier table that will actually be used by the IDCT
routine.
 * The multiplier table contents are IDCT-method-dependent.  To
support
 * application changes in IDCT method between scans, we can remake
the
 * multiplier tables if necessary.
 * In buffered-image mode, the first output pass may occur before
any data
 * has been seen for some components, and thus before their Q-tables
have
 * been saved away.  To handle this case, multiplier tables are
preset
 * to zeroes; the result of the IDCT will be a neutral gray level.
 */


/* Private subobject for this module */

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

  /* This array contains the IDCT method code that each multiplier
table
   * is currently set up for, or -1 if it's not yet set up.
   * The actual multiplier tables are pointed to by dct_table in the
   * per-component comp_info structures.
   */
  int cur_method[MAX_COMPONENTS];
} my_idct_controller;

typedef my_idct_controller * my_idct_ptr;


/* Allocated multiplier tables: big enough for any supported variant
*/

typedef union {
  ISLOW_MULT_TYPE islow_array[DCTSIZE2];
#ifdef DCT_IFAST_SUPPORTED
  IFAST_MULT_TYPE ifast_array[DCTSIZE2];
#endif
#ifdef DCT_FLOAT_SUPPORTED
  FLOAT_MULT_TYPE float_array[DCTSIZE2];
#endif
} multiplier_table;


/* The current scaled-IDCT routines require ISLOW-style multiplier
tables,
 * so be sure to compile that code if either ISLOW or SCALING is
requested.
 */
#ifdef DCT_ISLOW_SUPPORTED
#define PROVIDE_ISLOW_TABLES
#else
#ifdef IDCT_SCALING_SUPPORTED
#define PROVIDE_ISLOW_TABLES
#endif
#endif


/*
 * Prepare for an output pass.
 * Here we select the proper IDCT routine for each component and
build
 * a matching multiplier table.
 */

METHODDEF(void)
start_pass (j_decompress_ptr cinfo)
{
  my_idct_ptr idct = (my_idct_ptr) cinfo->idct;
  int ci, i;
  jpeg_component_info *compptr;
  int method = 0;
  inverse_DCT_method_ptr method_ptr = NULL;
  JQUANT_TBL * qtbl;

  for (ci = 0, compptr = cinfo->comp_info; ci <
cinfo->num_components;
       ci++, compptr++) {
    /* Select the proper IDCT routine for this component's scaling
*/
    switch (compptr->DCT_scaled_size) {
#ifdef IDCT_SCALING_SUPPORTED
    case 1:
      method_ptr = jpeg_idct_1x1;
      method = JDCT_ISLOW;        /* jidctred uses islow-style table */
      break;
    case 2:
      method_ptr = jpeg_idct_2x2;
      method = JDCT_ISLOW;        /* jidctred uses islow-style table */
      break;
    case 4:
      method_ptr = jpeg_idct_4x4;
      method = JDCT_ISLOW;        /* jidctred uses islow-style table */
      break;
#endif
    case DCTSIZE:
      method_ptr = jpeg_idct_islow;
      method = JDCT_ISLOW;
      break;

      switch (cinfo->dct_method) {
#ifdef DCT_ISLOW_SUPPORTED
      case JDCT_ISLOW:
        method_ptr = jpeg_idct_islow;
        method = JDCT_ISLOW;
        break;
#endif
#ifdef DCT_IFAST_SUPPORTED
      case JDCT_IFAST:
        method_ptr = jpeg_idct_islow;
        method = JDCT_ISLOW;
        break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
      case JDCT_FLOAT:
        method_ptr = jpeg_idct_islow;
        method = JDCT_ISLOW;
        break;
#endif
      default:
        ERREXIT(cinfo, JERR_NOT_COMPILED);
        break;
      }
      break;
    default:
      ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size);
      break;
    }
    idct->pub.inverse_DCT[ci] = method_ptr;
    /* Create multiplier table from quant table.
     * However, we can skip this if the component is uninteresting
     * or if we already built the table.  Also, if no quant table
     * has yet been saved for the component, we leave the
     * multiplier table all-zero; we'll be reading zeroes from the
     * coefficient controller's buffer anyway.
     */
    if (! compptr->component_needed || idct->cur_method[ci] ==
method)
      continue;
    qtbl = compptr->quant_table;
    if (qtbl == NULL)                /* happens if no data yet for component */
      continue;
    idct->cur_method[ci] = method;
    switch (method) {
#ifdef PROVIDE_ISLOW_TABLES
    case JDCT_ISLOW:
      {
        /* For LL&M IDCT method, multipliers are equal to raw quantization
         * coefficients, but are stored as ints to ensure access
efficiency.
         */
        ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
        for (i = 0; i < DCTSIZE2; i++) {
    ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[i];
    }
       }
       break;
#endif
#ifdef DCT_IFAST_SUPPORTED
     case JDCT_IFAST:
      {
        /* For LL&M IDCT method, multipliers are equal to raw quantization
         * coefficients, but are stored as ints to ensure access
efficiency.
         */
        ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
        for (i = 0; i < DCTSIZE2; i++) {
    ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[i];
    }
       }
       break;
#endif
#ifdef DCT_FLOAT_SUPPORTED
    case JDCT_FLOAT:
      {
        /* For LL&M IDCT method, multipliers are equal to raw quantization
         * coefficients, but are stored as ints to ensure access
efficiency.
         */
        ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
        for (i = 0; i < DCTSIZE2; i++) {
    ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[i];
    }
       }
       break;
#endif
    default:
      ERREXIT(cinfo, JERR_NOT_COMPILED);
      break;
      }
  }
}



/*
 * Initialize IDCT manager.
 */

GLOBAL(void)
jinit_inverse_dct (j_decompress_ptr cinfo)
{
  my_idct_ptr idct;
  int ci;
  jpeg_component_info *compptr;

  idct = (my_idct_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                SIZEOF(my_idct_controller));
  cinfo->idct = (struct jpeg_inverse_dct *) idct;
  idct->pub.start_pass = start_pass;

  for (ci = 0, compptr = cinfo->comp_info; ci <
cinfo->num_components;
       ci++, compptr++) {
    /* Allocate and pre-zero a multiplier table for each component
*/
    compptr->dct_table =
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                  SIZEOF(multiplier_table));
    MEMZERO(compptr->dct_table, SIZEOF(multiplier_table));
    /* Mark multiplier table not yet set up for any method */
    idct->cur_method[ci] = -1;
  }
}