text: /*
   * 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:
        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_ifast;
  	method = JDCT_IFAST;
  	break;
  #endif
  #ifdef DCT_FLOAT_SUPPORTED
        case JDCT_FLOAT:
  	method_ptr = jpeg_idct_float;
  	method = JDCT_FLOAT;
  	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 AA&N IDCT method, multipliers are equal to quantization
  	 * coefficients scaled by scalefactor[row]*scalefactor[col], where
  	 *   scalefactor[0] = 1
  	 *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
  	 * For integer operation, the multiplier table is to be scaled by
  	 * IFAST_SCALE_BITS.
  	 */
  	IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table;
  #define CONST_BITS 14
  	static const INT16 aanscales[DCTSIZE2] = {
  	  /* precomputed values scaled up by 14 bits */
  	  16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
  	  22725, 31521, 29692, 26722, 22725, 17855, 12299,  6270,
  	  21407, 29692, 27969, 25172, 21407, 16819, 11585,  5906,
  	  19266, 26722, 25172, 22654, 19266, 15137, 10426,  5315,
  	  16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
  	  12873, 17855, 16819, 15137, 12873, 10114,  6967,  3552,
  	   8867, 12299, 11585, 10426,  8867,  6967,  4799,  2446,
  	   4520,  6270,  5906,  5315,  4520,  3552,  2446,  1247
  	};
  	SHIFT_TEMPS
  
  	for (i = 0; i < DCTSIZE2; i++) {
  	  ifmtbl[i] = (IFAST_MULT_TYPE)
  	    DESCALE(MULTIPLY16V16((JPEG_INT32) qtbl->quantval[i],
  				  (JPEG_INT32) aanscales[i]),
  		    CONST_BITS-IFAST_SCALE_BITS);
  	}
        }
        break;
  #endif
  #ifdef DCT_FLOAT_SUPPORTED
      case JDCT_FLOAT:
        {
  	/* For float AA&N IDCT method, multipliers are equal to quantization
  	 * coefficients scaled by scalefactor[row]*scalefactor[col], where
  	 *   scalefactor[0] = 1
  	 *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
  	 */
  	FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table;
  	int row, col;
  	static const double aanscalefactor[DCTSIZE] = {
  	  1.0, 1.387039845, 1.306562965, 1.175875602,
  	  1.0, 0.785694958, 0.541196100, 0.275899379
  	};
  
  	i = 0;
  	for (row = 0; row < DCTSIZE; row++) {
  	  for (col = 0; col < DCTSIZE; col++) {
  	    fmtbl[i] = (FLOAT_MULT_TYPE)
  	      ((double) qtbl->quantval[i] *
  	       aanscalefactor[row] * aanscalefactor[col]);
  	    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;
    }
  }
  