/* * 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((INT32) qtbl->quantval[i],				  (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;  }}