    /*
     * 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 short 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((long) qtbl->quantval[i],
    				  (long) 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;
      }
    }