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 } 270
