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jddctmgr.c (8293B)
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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 }