1/*
2 * reserved comment block
3 * DO NOT REMOVE OR ALTER!
4 */
5/*
6 * jddctmgr.c
7 *
8 * Copyright (C) 1994-1996, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
10 * For conditions of distribution and use, see the accompanying README file.
11 *
12 * This file contains the inverse-DCT management logic.
13 * This code selects a particular IDCT implementation to be used,
14 * and it performs related housekeeping chores. No code in this file
15 * is executed per IDCT step, only during output pass setup.
16 *
17 * Note that the IDCT routines are responsible for performing coefficient
18 * dequantization as well as the IDCT proper. This module sets up the
19 * dequantization multiplier table needed by the IDCT routine.
20 */
21
22#define JPEG_INTERNALS
23#include "jinclude.h"
24#include "jpeglib.h"
25#include "jdct.h" /* Private declarations for DCT subsystem */
26
27
28/*
29 * The decompressor input side (jdinput.c) saves away the appropriate
30 * quantization table for each component at the start of the first scan
31 * involving that component. (This is necessary in order to correctly
32 * decode files that reuse Q-table slots.)
33 * When we are ready to make an output pass, the saved Q-table is converted
34 * to a multiplier table that will actually be used by the IDCT routine.
35 * The multiplier table contents are IDCT-method-dependent. To support
36 * application changes in IDCT method between scans, we can remake the
37 * multiplier tables if necessary.
38 * In buffered-image mode, the first output pass may occur before any data
39 * has been seen for some components, and thus before their Q-tables have
40 * been saved away. To handle this case, multiplier tables are preset
41 * to zeroes; the result of the IDCT will be a neutral gray level.
42 */
43
44
45/* Private subobject for this module */
46
47typedef struct {
48 struct jpeg_inverse_dct pub; /* public fields */
49
50 /* This array contains the IDCT method code that each multiplier table
51 * is currently set up for, or -1 if it's not yet set up.
52 * The actual multiplier tables are pointed to by dct_table in the
53 * per-component comp_info structures.
54 */
55 int cur_method[MAX_COMPONENTS];
56} my_idct_controller;
57
58typedef my_idct_controller * my_idct_ptr;
59
60
61/* Allocated multiplier tables: big enough for any supported variant */
62
63typedef union {
64 ISLOW_MULT_TYPE islow_array[DCTSIZE2];
65#ifdef DCT_IFAST_SUPPORTED
66 IFAST_MULT_TYPE ifast_array[DCTSIZE2];
67#endif
68#ifdef DCT_FLOAT_SUPPORTED
69 FLOAT_MULT_TYPE float_array[DCTSIZE2];
70#endif
71} multiplier_table;
72
73
74/* The current scaled-IDCT routines require ISLOW-style multiplier tables,
75 * so be sure to compile that code if either ISLOW or SCALING is requested.
76 */
77#ifdef DCT_ISLOW_SUPPORTED
78#define PROVIDE_ISLOW_TABLES
79#else
80#ifdef IDCT_SCALING_SUPPORTED
81#define PROVIDE_ISLOW_TABLES
82#endif
83#endif
84
85
86/*
87 * Prepare for an output pass.
88 * Here we select the proper IDCT routine for each component and build
89 * a matching multiplier table.
90 */
91
92METHODDEF(void)
93start_pass (j_decompress_ptr cinfo)
94{
95 my_idct_ptr idct = (my_idct_ptr) cinfo->idct;
96 int ci, i;
97 jpeg_component_info *compptr;
98 int method = 0;
99 inverse_DCT_method_ptr method_ptr = NULL;
100 JQUANT_TBL * qtbl;
101
102 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
103 ci++, compptr++) {
104 /* Select the proper IDCT routine for this component's scaling */
105 switch (compptr->DCT_scaled_size) {
106#ifdef IDCT_SCALING_SUPPORTED
107 case 1:
108 method_ptr = jpeg_idct_1x1;
109 method = JDCT_ISLOW; /* jidctred uses islow-style table */
110 break;
111 case 2:
112 method_ptr = jpeg_idct_2x2;
113 method = JDCT_ISLOW; /* jidctred uses islow-style table */
114 break;
115 case 4:
116 method_ptr = jpeg_idct_4x4;
117 method = JDCT_ISLOW; /* jidctred uses islow-style table */
118 break;
119#endif
120 case DCTSIZE:
121 switch (cinfo->dct_method) {
122#ifdef DCT_ISLOW_SUPPORTED
123 case JDCT_ISLOW:
124 method_ptr = jpeg_idct_islow;
125 method = JDCT_ISLOW;
126 break;
127#endif
128#ifdef DCT_IFAST_SUPPORTED
129 case JDCT_IFAST:
130 method_ptr = jpeg_idct_ifast;
131 method = JDCT_IFAST;
132 break;
133#endif
134#ifdef DCT_FLOAT_SUPPORTED
135 case JDCT_FLOAT:
136 method_ptr = jpeg_idct_float;
137 method = JDCT_FLOAT;
138 break;
139#endif
140 default:
141 ERREXIT(cinfo, JERR_NOT_COMPILED);
142 break;
143 }
144 break;
145 default:
146 ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size);
147 break;
148 }
149 idct->pub.inverse_DCT[ci] = method_ptr;
150 /* Create multiplier table from quant table.
151 * However, we can skip this if the component is uninteresting
152 * or if we already built the table. Also, if no quant table
153 * has yet been saved for the component, we leave the
154 * multiplier table all-zero; we'll be reading zeroes from the
155 * coefficient controller's buffer anyway.
156 */
157 if (! compptr->component_needed || idct->cur_method[ci] == method)
158 continue;
159 qtbl = compptr->quant_table;
160 if (qtbl == NULL) /* happens if no data yet for component */
161 continue;
162 idct->cur_method[ci] = method;
163 switch (method) {
164#ifdef PROVIDE_ISLOW_TABLES
165 case JDCT_ISLOW:
166 {
167 /* For LL&M IDCT method, multipliers are equal to raw quantization
168 * coefficients, but are stored as ints to ensure access efficiency.
169 */
170 ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
171 for (i = 0; i < DCTSIZE2; i++) {
172 ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[i];
173 }
174 }
175 break;
176#endif
177#ifdef DCT_IFAST_SUPPORTED
178 case JDCT_IFAST:
179 {
180 /* For AA&N IDCT method, multipliers are equal to quantization
181 * coefficients scaled by scalefactor[row]*scalefactor[col], where
182 * scalefactor[0] = 1
183 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
184 * For integer operation, the multiplier table is to be scaled by
185 * IFAST_SCALE_BITS.
186 */
187 IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table;
188#define CONST_BITS 14
189 static const INT16 aanscales[DCTSIZE2] = {
190 /* precomputed values scaled up by 14 bits */
191 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
192 22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270,
193 21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906,
194 19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315,
195 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
196 12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552,
197 8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446,
198 4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247
199 };
200 SHIFT_TEMPS
201
202 for (i = 0; i < DCTSIZE2; i++) {
203 ifmtbl[i] = (IFAST_MULT_TYPE)
204 DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i],
205 (INT32) aanscales[i]),
206 CONST_BITS-IFAST_SCALE_BITS);
207 }
208 }
209 break;
210#endif
211#ifdef DCT_FLOAT_SUPPORTED
212 case JDCT_FLOAT:
213 {
214 /* For float AA&N IDCT method, multipliers are equal to quantization
215 * coefficients scaled by scalefactor[row]*scalefactor[col], where
216 * scalefactor[0] = 1
217 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
218 */
219 FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table;
220 int row, col;
221 static const double aanscalefactor[DCTSIZE] = {
222 1.0, 1.387039845, 1.306562965, 1.175875602,
223 1.0, 0.785694958, 0.541196100, 0.275899379
224 };
225
226 i = 0;
227 for (row = 0; row < DCTSIZE; row++) {
228 for (col = 0; col < DCTSIZE; col++) {
229 fmtbl[i] = (FLOAT_MULT_TYPE)
230 ((double) qtbl->quantval[i] *
231 aanscalefactor[row] * aanscalefactor[col]);
232 i++;
233 }
234 }
235 }
236 break;
237#endif
238 default:
239 ERREXIT(cinfo, JERR_NOT_COMPILED);
240 break;
241 }
242 }
243}
244
245
246/*
247 * Initialize IDCT manager.
248 */
249
250GLOBAL(void)
251jinit_inverse_dct (j_decompress_ptr cinfo)
252{
253 my_idct_ptr idct;
254 int ci;
255 jpeg_component_info *compptr;
256
257 idct = (my_idct_ptr)
258 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
259 SIZEOF(my_idct_controller));
260 cinfo->idct = (struct jpeg_inverse_dct *) idct;
261 idct->pub.start_pass = start_pass;
262
263 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
264 ci++, compptr++) {
265 /* Allocate and pre-zero a multiplier table for each component */
266 compptr->dct_table =
267 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
268 SIZEOF(multiplier_table));
269 MEMZERO(compptr->dct_table, SIZEOF(multiplier_table));
270 /* Mark multiplier table not yet set up for any method */
271 idct->cur_method[ci] = -1;
272 }
273}
274