src/jpeg/jddctmgr.c

   1 /*
   2  * jddctmgr.c
   3  *
   4  * Copyright (C) 1994-1996, Thomas G. Lane.
   5  * This file is part of the Independent JPEG Group's software.
   6  * For conditions of distribution and use, see the accompanying README file.
   7  *
   8  * This file contains the inverse-DCT management logic.
   9  * This code selects a particular IDCT implementation to be used,
  10  * and it performs related housekeeping chores.  No code in this file
  11  * is executed per IDCT step, only during output pass setup.
  12  *
  13  * Note that the IDCT routines are responsible for performing coefficient
  14  * dequantization as well as the IDCT proper.  This module sets up the
  15  * dequantization multiplier table needed by the IDCT routine.
  16  */
  17
  18 #define JPEG_INTERNALS
  19 #include "jinclude.h"
  20 #include "jpeglib.h"
  21 #include "jdct.h"               /* Private declarations for DCT subsystem */
  22
  23
  24 /*
  25  * The decompressor input side (jdinput.c) saves away the appropriate
  26  * quantization table for each component at the start of the first scan
  27  * involving that component.  (This is necessary in order to correctly
  28  * decode files that reuse Q-table slots.)
  29  * When we are ready to make an output pass, the saved Q-table is converted
  30  * to a multiplier table that will actually be used by the IDCT routine.
  31  * The multiplier table contents are IDCT-method-dependent.  To support
  32  * application changes in IDCT method between scans, we can remake the
  33  * multiplier tables if necessary.
  34  * In buffered-image mode, the first output pass may occur before any data
  35  * has been seen for some components, and thus before their Q-tables have
  36  * been saved away.  To handle this case, multiplier tables are preset
  37  * to zeroes; the result of the IDCT will be a neutral gray level.
  38  */
  39
  40
  41 /* Private subobject for this module */
  42
  43 typedef struct {
  44   struct jpeg_inverse_dct pub;  /* public fields */
  45
  46   /* This array contains the IDCT method code that each multiplier table
  47    * is currently set up for, or -1 if it's not yet set up.
  48    * The actual multiplier tables are pointed to by dct_table in the
  49    * per-component comp_info structures.
  50    */
  51   int cur_method[MAX_COMPONENTS];
  52 } my_idct_controller;
  53
  54 typedef my_idct_controller * my_idct_ptr;
  55
  56
  57 /* Allocated multiplier tables: big enough for any supported variant */
  58
  59 typedef union {
  60   ISLOW_MULT_TYPE islow_array[DCTSIZE2];
  61 #ifdef DCT_IFAST_SUPPORTED
  62   IFAST_MULT_TYPE ifast_array[DCTSIZE2];
  63 #endif
  64 #ifdef DCT_FLOAT_SUPPORTED
  65   FLOAT_MULT_TYPE float_array[DCTSIZE2];
  66 #endif
  67 } multiplier_table;
  68
  69
  70 /* The current scaled-IDCT routines require ISLOW-style multiplier tables,
  71  * so be sure to compile that code if either ISLOW or SCALING is requested.
  72  */
  73 #ifdef DCT_ISLOW_SUPPORTED
  74 #define PROVIDE_ISLOW_TABLES
  75 #else
  76 #ifdef IDCT_SCALING_SUPPORTED
  77 #define PROVIDE_ISLOW_TABLES
  78 #endif
  79 #endif
  80
  81
  82 /*
  83  * Prepare for an output pass.
  84  * Here we select the proper IDCT routine for each component and build
  85  * a matching multiplier table.
  86  */
  87
  88 METHODDEF(void)
  89 start_pass (j_decompress_ptr cinfo)
  90 {
  91   my_idct_ptr idct = (my_idct_ptr) cinfo->idct;
  92   int ci, i;
  93   jpeg_component_info *compptr;
  94   int method = 0;
  95   inverse_DCT_method_ptr method_ptr = NULL;
  96   JQUANT_TBL * qtbl;
  97
  98   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
  99        ci++, compptr++) {
 100     /* Select the proper IDCT routine for this component's scaling */
 101     switch (compptr->DCT_scaled_size) {
 102 #ifdef IDCT_SCALING_SUPPORTED
 103     case 1:
 104       method_ptr = jpeg_idct_1x1;
 105       method = JDCT_ISLOW;      /* jidctred uses islow-style table */
 106       break;
 107     case 2:
 108       method_ptr = jpeg_idct_2x2;
 109       method = JDCT_ISLOW;      /* jidctred uses islow-style table */
 110       break;
 111     case 4:
 112       method_ptr = jpeg_idct_4x4;
 113       method = JDCT_ISLOW;      /* jidctred uses islow-style table */
 114       break;
 115 #endif
 116     case DCTSIZE:
 117       switch (cinfo->dct_method) {
 118 #ifdef DCT_ISLOW_SUPPORTED
 119       case JDCT_ISLOW:
 120         method_ptr = jpeg_idct_islow;
 121         method = JDCT_ISLOW;
 122         break;
 123 #endif
 124 #ifdef DCT_IFAST_SUPPORTED
 125       case JDCT_IFAST:
 126         method_ptr = jpeg_idct_ifast;
 127         method = JDCT_IFAST;
 128         break;
 129 #endif
 130 #ifdef DCT_FLOAT_SUPPORTED
 131       case JDCT_FLOAT:
 132         method_ptr = jpeg_idct_float;
 133         method = JDCT_FLOAT;
 134         break;
 135 #endif
 136       default:
 137         ERREXIT(cinfo, JERR_NOT_COMPILED);
 138         break;
 139       }
 140       break;
 141     default:
 142       ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size);
 143       break;
 144     }
 145     idct->pub.inverse_DCT[ci] = method_ptr;
 146     /* Create multiplier table from quant table.
 147      * However, we can skip this if the component is uninteresting
 148      * or if we already built the table.  Also, if no quant table
 149      * has yet been saved for the component, we leave the
 150      * multiplier table all-zero; we'll be reading zeroes from the
 151      * coefficient controller's buffer anyway.
 152      */
 153     if (! compptr->component_needed || idct->cur_method[ci] == method)
 154       continue;
 155     qtbl = compptr->quant_table;
 156     if (qtbl == NULL)           /* happens if no data yet for component */
 157       continue;
 158     idct->cur_method[ci] = method;
 159     switch (method) {
 160 #ifdef PROVIDE_ISLOW_TABLES
 161     case JDCT_ISLOW:
 162       {
 163         /* For LL&M IDCT method, multipliers are equal to raw quantization
 164          * coefficients, but are stored as ints to ensure access efficiency.
 165          */
 166         ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
 167         for (i = 0; i < DCTSIZE2; i++) {
 168           ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[i];
 169         }
 170       }
 171       break;
 172 #endif
 173 #ifdef DCT_IFAST_SUPPORTED
 174     case JDCT_IFAST:
 175       {
 176         /* For AA&N IDCT method, multipliers are equal to quantization
 177          * coefficients scaled by scalefactor[row]*scalefactor[col], where
 178          *   scalefactor[0] = 1
 179          *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
 180          * For integer operation, the multiplier table is to be scaled by
 181          * IFAST_SCALE_BITS.
 182          */
 183         IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table;
 184 #define CONST_BITS 14
 185         static const INT16 aanscales[DCTSIZE2] = {
 186           /* precomputed values scaled up by 14 bits */
 187           16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
 188           22725, 31521, 29692, 26722, 22725, 17855, 12299,  6270,
 189           21407, 29692, 27969, 25172, 21407, 16819, 11585,  5906,
 190           19266, 26722, 25172, 22654, 19266, 15137, 10426,  5315,
 191           16384, 22725, 21407, 19266, 16384, 12873,  8867,  4520,
 192           12873, 17855, 16819, 15137, 12873, 10114,  6967,  3552,
 193            8867, 12299, 11585, 10426,  8867,  6967,  4799,  2446,
 194            4520,  6270,  5906,  5315,  4520,  3552,  2446,  1247
 195         };
 196         SHIFT_TEMPS
 197
 198         for (i = 0; i < DCTSIZE2; i++) {
 199           ifmtbl[i] = (IFAST_MULT_TYPE)
 200             DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i],
 201                                   (INT32) aanscales[i]),
 202                     CONST_BITS-IFAST_SCALE_BITS);
 203         }
 204       }
 205       break;
 206 #endif
 207 #ifdef DCT_FLOAT_SUPPORTED
 208     case JDCT_FLOAT:
 209       {
 210         /* For float AA&N IDCT method, multipliers are equal to quantization
 211          * coefficients scaled by scalefactor[row]*scalefactor[col], where
 212          *   scalefactor[0] = 1
 213          *   scalefactor[k] = cos(k*PI/16) * sqrt(2)    for k=1..7
 214          */
 215         FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table;
 216         int row, col;
 217         static const double aanscalefactor[DCTSIZE] = {
 218           1.0, 1.387039845, 1.306562965, 1.175875602,
 219           1.0, 0.785694958, 0.541196100, 0.275899379
 220         };
 221
 222         i = 0;
 223         for (row = 0; row < DCTSIZE; row++) {
 224           for (col = 0; col < DCTSIZE; col++) {
 225             fmtbl[i] = (FLOAT_MULT_TYPE)
 226               ((double) qtbl->quantval[i] *
 227                aanscalefactor[row] * aanscalefactor[col]);
 228             i++;
 229           }
 230         }
 231       }
 232       break;
 233 #endif
 234     default:
 235       ERREXIT(cinfo, JERR_NOT_COMPILED);
 236       break;
 237     }
 238   }
 239 }
 240
 241
 242 /*
 243  * Initialize IDCT manager.
 244  */
 245
 246 GLOBAL(void)
 247 jinit_inverse_dct (j_decompress_ptr cinfo)
 248 {
 249   my_idct_ptr idct;
 250   int ci;
 251   jpeg_component_info *compptr;
 252
 253   idct = (my_idct_ptr)
 254     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 255                                 SIZEOF(my_idct_controller));
 256   cinfo->idct = (struct jpeg_inverse_dct *) idct;
 257   idct->pub.start_pass = start_pass;
 258
 259   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 260        ci++, compptr++) {
 261     /* Allocate and pre-zero a multiplier table for each component */
 262     compptr->dct_table =
 263       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 264                                   SIZEOF(multiplier_table));
 265     MEMZERO(compptr->dct_table, SIZEOF(multiplier_table));
 266     /* Mark multiplier table not yet set up for any method */
 267     idct->cur_method[ci] = -1;
 268   }
 269 }