jddctmgr.cpp (10304B)
1 /* 2 * jddctmgr.c 3 * 4 * Copyright (C) 1994-1995, 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 my_idct_ptr idct = (my_idct_ptr) cinfo->idct; 91 int ci, i; 92 jpeg_component_info * compptr; 93 int method = 0; 94 inverse_DCT_method_ptr method_ptr = NULL; 95 JQUANT_TBL * qtbl; 96 97 for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 98 ci++, compptr++ ) { 99 /* Select the proper IDCT routine for this component's scaling */ 100 switch ( compptr->DCT_scaled_size ) { 101 #ifdef IDCT_SCALING_SUPPORTED 102 case 1: 103 method_ptr = jpeg_idct_1x1; 104 method = JDCT_ISLOW;/* jidctred uses islow-style table */ 105 break; 106 case 2: 107 method_ptr = jpeg_idct_2x2; 108 method = JDCT_ISLOW;/* jidctred uses islow-style table */ 109 break; 110 case 4: 111 method_ptr = jpeg_idct_4x4; 112 method = JDCT_ISLOW;/* jidctred uses islow-style table */ 113 break; 114 #endif 115 case DCTSIZE: 116 switch ( cinfo->dct_method ) { 117 #ifdef DCT_ISLOW_SUPPORTED 118 case JDCT_ISLOW: 119 method_ptr = jpeg_idct_islow; 120 method = JDCT_ISLOW; 121 break; 122 #endif 123 #ifdef DCT_IFAST_SUPPORTED 124 case JDCT_IFAST: 125 method_ptr = jpeg_idct_ifast; 126 method = JDCT_IFAST; 127 break; 128 #endif 129 #ifdef DCT_FLOAT_SUPPORTED 130 case JDCT_FLOAT: 131 method_ptr = jpeg_idct_float; 132 method = JDCT_FLOAT; 133 break; 134 #endif 135 default: 136 ERREXIT( cinfo, JERR_NOT_COMPILED ); 137 break; 138 } 139 break; 140 default: 141 ERREXIT1( cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size ); 142 break; 143 } 144 idct->pub.inverse_DCT[ci] = method_ptr; 145 /* Create multiplier table from quant table. 146 * However, we can skip this if the component is uninteresting 147 * or if we already built the table. Also, if no quant table 148 * has yet been saved for the component, we leave the 149 * multiplier table all-zero; we'll be reading zeroes from the 150 * coefficient controller's buffer anyway. 151 */ 152 if ( ( !compptr->component_needed ) || ( idct->cur_method[ci] == method ) ) { 153 continue; 154 } 155 qtbl = compptr->quant_table; 156 if ( qtbl == NULL ) {/* happens if no data yet for component */ 157 continue; 158 } 159 idct->cur_method[ci] = method; 160 switch ( method ) { 161 #ifdef PROVIDE_ISLOW_TABLES 162 case JDCT_ISLOW: 163 { 164 /* For LL&M IDCT method, multipliers are equal to raw quantization 165 * coefficients, but are stored in natural order as ints. 166 */ 167 ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table; 168 for ( i = 0; i < DCTSIZE2; i++ ) { 169 ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[jpeg_zigzag_order[i]]; 170 } 171 } 172 break; 173 #endif 174 #ifdef DCT_IFAST_SUPPORTED 175 case JDCT_IFAST: 176 { 177 /* For AA&N IDCT method, multipliers are equal to quantization 178 * coefficients scaled by scalefactor[row]*scalefactor[col], where 179 * scalefactor[0] = 1 180 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7 181 * For integer operation, the multiplier table is to be scaled by 182 * IFAST_SCALE_BITS. The multipliers are stored in natural order. 183 */ 184 IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table; 185 #define CONST_BITS 14 186 static const INT16 aanscales[DCTSIZE2] = { 187 /* precomputed values scaled up by 14 bits */ 188 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520, 189 22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270, 190 21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906, 191 19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315, 192 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520, 193 12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552, 194 8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446, 195 4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247 196 }; 197 SHIFT_TEMPS 198 199 for ( i = 0; i < DCTSIZE2; i++ ) { 200 ifmtbl[i] = (IFAST_MULT_TYPE) 201 DESCALE( MULTIPLY16V16( (INT32) qtbl->quantval[jpeg_zigzag_order[i]], 202 (INT32) aanscales[i] ), 203 CONST_BITS - IFAST_SCALE_BITS ); 204 } 205 } 206 break; 207 #endif 208 #ifdef DCT_FLOAT_SUPPORTED 209 case JDCT_FLOAT: 210 { 211 /* For float AA&N IDCT method, multipliers are equal to quantization 212 * coefficients scaled by scalefactor[row]*scalefactor[col], where 213 * scalefactor[0] = 1 214 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7 215 * The multipliers are stored in natural order. 216 */ 217 FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table; 218 int row, col; 219 static const double aanscalefactor[DCTSIZE] = { 220 1.0, 1.387039845, 1.306562965, 1.175875602, 221 1.0, 0.785694958, 0.541196100, 0.275899379 222 }; 223 224 i = 0; 225 for ( row = 0; row < DCTSIZE; row++ ) { 226 for ( col = 0; col < DCTSIZE; col++ ) { 227 fmtbl[i] = (FLOAT_MULT_TYPE) 228 ( (double) qtbl->quantval[jpeg_zigzag_order[i]] * 229 aanscalefactor[row] * aanscalefactor[col] ); 230 i++; 231 } 232 } 233 } 234 break; 235 #endif 236 default: 237 ERREXIT( cinfo, JERR_NOT_COMPILED ); 238 break; 239 } 240 } 241 } 242 243 244 /* 245 * Initialize IDCT manager. 246 */ 247 248 GLOBAL void 249 jinit_inverse_dct( j_decompress_ptr cinfo ) { 250 my_idct_ptr idct; 251 int ci; 252 jpeg_component_info * compptr; 253 254 idct = (my_idct_ptr) 255 ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE, 256 SIZEOF( my_idct_controller ) ); 257 cinfo->idct = (struct jpeg_inverse_dct *) idct; 258 idct->pub.start_pass = start_pass; 259 260 for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 261 ci++, compptr++ ) { 262 /* Allocate and pre-zero a multiplier table for each component */ 263 compptr->dct_table = 264 ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE, 265 SIZEOF( multiplier_table ) ); 266 MEMZERO( compptr->dct_table, SIZEOF( multiplier_table ) ); 267 /* Mark multiplier table not yet set up for any method */ 268 idct->cur_method[ci] = -1; 269 } 270 }