4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1994-1996, Thomas G. Lane.
6 * Modified 2002-2010 by Guido Vollbeding.
7 * libjpeg-turbo Modifications:
8 * Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
9 * Copyright (C) 2010, 2015, 2022, D. R. Commander.
10 * Copyright (C) 2013, MIPS Technologies, Inc., California.
11 * For conditions of distribution and use, see the accompanying README.ijg
14 * This file contains the inverse-DCT management logic.
15 * This code selects a particular IDCT implementation to be used,
16 * and it performs related housekeeping chores. No code in this file
17 * is executed per IDCT step, only during output pass setup.
19 * Note that the IDCT routines are responsible for performing coefficient
20 * dequantization as well as the IDCT proper. This module sets up the
21 * dequantization multiplier table needed by the IDCT routine.
24 #define JPEG_INTERNALS
27 #include "jdct.h" /* Private declarations for DCT subsystem */
33 * The decompressor input side (jdinput.c) saves away the appropriate
34 * quantization table for each component at the start of the first scan
35 * involving that component. (This is necessary in order to correctly
36 * decode files that reuse Q-table slots.)
37 * When we are ready to make an output pass, the saved Q-table is converted
38 * to a multiplier table that will actually be used by the IDCT routine.
39 * The multiplier table contents are IDCT-method-dependent. To support
40 * application changes in IDCT method between scans, we can remake the
41 * multiplier tables if necessary.
42 * In buffered-image mode, the first output pass may occur before any data
43 * has been seen for some components, and thus before their Q-tables have
44 * been saved away. To handle this case, multiplier tables are preset
45 * to zeroes; the result of the IDCT will be a neutral gray level.
49 /* Private subobject for this module */
52 struct jpeg_inverse_dct pub; /* public fields */
54 /* This array contains the IDCT method code that each multiplier table
55 * is currently set up for, or -1 if it's not yet set up.
56 * The actual multiplier tables are pointed to by dct_table in the
57 * per-component comp_info structures.
59 int cur_method[MAX_COMPONENTS];
62 typedef my_idct_controller *my_idct_ptr;
65 /* Allocated multiplier tables: big enough for any supported variant */
68 ISLOW_MULT_TYPE islow_array[DCTSIZE2];
69 #ifdef DCT_IFAST_SUPPORTED
70 IFAST_MULT_TYPE ifast_array[DCTSIZE2];
72 #ifdef DCT_FLOAT_SUPPORTED
73 FLOAT_MULT_TYPE float_array[DCTSIZE2];
78 /* The current scaled-IDCT routines require ISLOW-style multiplier tables,
79 * so be sure to compile that code if either ISLOW or SCALING is requested.
81 #ifdef DCT_ISLOW_SUPPORTED
82 #define PROVIDE_ISLOW_TABLES
84 #ifdef IDCT_SCALING_SUPPORTED
85 #define PROVIDE_ISLOW_TABLES
91 * Prepare for an output pass.
92 * Here we select the proper IDCT routine for each component and build
93 * a matching multiplier table.
97 start_pass(j_decompress_ptr cinfo)
99 my_idct_ptr idct = (my_idct_ptr)cinfo->idct;
101 jpeg_component_info *compptr;
103 inverse_DCT_method_ptr method_ptr = NULL;
106 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
108 /* Select the proper IDCT routine for this component's scaling */
109 switch (compptr->_DCT_scaled_size) {
110 #ifdef IDCT_SCALING_SUPPORTED
112 method_ptr = jpeg_idct_1x1;
113 method = JDCT_ISLOW; /* jidctred uses islow-style table */
116 if (jsimd_can_idct_2x2())
117 method_ptr = jsimd_idct_2x2;
119 method_ptr = jpeg_idct_2x2;
120 method = JDCT_ISLOW; /* jidctred uses islow-style table */
123 method_ptr = jpeg_idct_3x3;
124 method = JDCT_ISLOW; /* jidctint uses islow-style table */
127 if (jsimd_can_idct_4x4())
128 method_ptr = jsimd_idct_4x4;
130 method_ptr = jpeg_idct_4x4;
131 method = JDCT_ISLOW; /* jidctred uses islow-style table */
134 method_ptr = jpeg_idct_5x5;
135 method = JDCT_ISLOW; /* jidctint uses islow-style table */
138 #if defined(__mips__)
139 if (jsimd_can_idct_6x6())
140 method_ptr = jsimd_idct_6x6;
143 method_ptr = jpeg_idct_6x6;
144 method = JDCT_ISLOW; /* jidctint uses islow-style table */
147 method_ptr = jpeg_idct_7x7;
148 method = JDCT_ISLOW; /* jidctint uses islow-style table */
152 switch (cinfo->dct_method) {
153 #ifdef DCT_ISLOW_SUPPORTED
155 if (jsimd_can_idct_islow())
156 method_ptr = jsimd_idct_islow;
158 method_ptr = jpeg_idct_islow;
162 #ifdef DCT_IFAST_SUPPORTED
164 if (jsimd_can_idct_ifast())
165 method_ptr = jsimd_idct_ifast;
167 method_ptr = jpeg_idct_ifast;
171 #ifdef DCT_FLOAT_SUPPORTED
173 if (jsimd_can_idct_float())
174 method_ptr = jsimd_idct_float;
176 method_ptr = jpeg_idct_float;
181 ERREXIT(cinfo, JERR_NOT_COMPILED);
185 #ifdef IDCT_SCALING_SUPPORTED
187 method_ptr = jpeg_idct_9x9;
188 method = JDCT_ISLOW; /* jidctint uses islow-style table */
191 method_ptr = jpeg_idct_10x10;
192 method = JDCT_ISLOW; /* jidctint uses islow-style table */
195 method_ptr = jpeg_idct_11x11;
196 method = JDCT_ISLOW; /* jidctint uses islow-style table */
199 #if defined(__mips__)
200 if (jsimd_can_idct_12x12())
201 method_ptr = jsimd_idct_12x12;
204 method_ptr = jpeg_idct_12x12;
205 method = JDCT_ISLOW; /* jidctint uses islow-style table */
208 method_ptr = jpeg_idct_13x13;
209 method = JDCT_ISLOW; /* jidctint uses islow-style table */
212 method_ptr = jpeg_idct_14x14;
213 method = JDCT_ISLOW; /* jidctint uses islow-style table */
216 method_ptr = jpeg_idct_15x15;
217 method = JDCT_ISLOW; /* jidctint uses islow-style table */
220 method_ptr = jpeg_idct_16x16;
221 method = JDCT_ISLOW; /* jidctint uses islow-style table */
225 ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->_DCT_scaled_size);
228 idct->pub.inverse_DCT[ci] = method_ptr;
229 /* Create multiplier table from quant table.
230 * However, we can skip this if the component is uninteresting
231 * or if we already built the table. Also, if no quant table
232 * has yet been saved for the component, we leave the
233 * multiplier table all-zero; we'll be reading zeroes from the
234 * coefficient controller's buffer anyway.
236 if (!compptr->component_needed || idct->cur_method[ci] == method)
238 qtbl = compptr->quant_table;
239 if (qtbl == NULL) /* happens if no data yet for component */
241 idct->cur_method[ci] = method;
243 #ifdef PROVIDE_ISLOW_TABLES
246 /* For LL&M IDCT method, multipliers are equal to raw quantization
247 * coefficients, but are stored as ints to ensure access efficiency.
249 ISLOW_MULT_TYPE *ismtbl = (ISLOW_MULT_TYPE *)compptr->dct_table;
250 for (i = 0; i < DCTSIZE2; i++) {
251 ismtbl[i] = (ISLOW_MULT_TYPE)qtbl->quantval[i];
256 #ifdef DCT_IFAST_SUPPORTED
259 /* For AA&N IDCT method, multipliers are equal to quantization
260 * coefficients scaled by scalefactor[row]*scalefactor[col], where
262 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
263 * For integer operation, the multiplier table is to be scaled by
266 IFAST_MULT_TYPE *ifmtbl = (IFAST_MULT_TYPE *)compptr->dct_table;
267 #define CONST_BITS 14
268 static const INT16 aanscales[DCTSIZE2] = {
269 /* precomputed values scaled up by 14 bits */
270 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
271 22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270,
272 21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906,
273 19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315,
274 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
275 12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552,
276 8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446,
277 4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247
281 for (i = 0; i < DCTSIZE2; i++) {
282 ifmtbl[i] = (IFAST_MULT_TYPE)
283 DESCALE(MULTIPLY16V16((JLONG)qtbl->quantval[i],
284 (JLONG)aanscales[i]),
285 CONST_BITS - IFAST_SCALE_BITS);
290 #ifdef DCT_FLOAT_SUPPORTED
293 /* For float AA&N IDCT method, multipliers are equal to quantization
294 * coefficients scaled by scalefactor[row]*scalefactor[col], where
296 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
298 FLOAT_MULT_TYPE *fmtbl = (FLOAT_MULT_TYPE *)compptr->dct_table;
300 static const double aanscalefactor[DCTSIZE] = {
301 1.0, 1.387039845, 1.306562965, 1.175875602,
302 1.0, 0.785694958, 0.541196100, 0.275899379
306 for (row = 0; row < DCTSIZE; row++) {
307 for (col = 0; col < DCTSIZE; col++) {
308 fmtbl[i] = (FLOAT_MULT_TYPE)
309 ((double)qtbl->quantval[i] *
310 aanscalefactor[row] * aanscalefactor[col]);
318 ERREXIT(cinfo, JERR_NOT_COMPILED);
326 * Initialize IDCT manager.
330 jinit_inverse_dct(j_decompress_ptr cinfo)
334 jpeg_component_info *compptr;
337 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
338 sizeof(my_idct_controller));
339 cinfo->idct = (struct jpeg_inverse_dct *)idct;
340 idct->pub.start_pass = start_pass;
342 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
344 /* Allocate and pre-zero a multiplier table for each component */
346 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
347 sizeof(multiplier_table));
348 memset(compptr->dct_table, 0, sizeof(multiplier_table));
349 /* Mark multiplier table not yet set up for any method */
350 idct->cur_method[ci] = -1;