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 */
29 #include "jpegapicomp.h"
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 */
117 if (jsimd_can_idct_2x2())
118 method_ptr = jsimd_idct_2x2;
121 method_ptr = _jpeg_idct_2x2;
122 method = JDCT_ISLOW; /* jidctred uses islow-style table */
125 method_ptr = _jpeg_idct_3x3;
126 method = JDCT_ISLOW; /* jidctint uses islow-style table */
130 if (jsimd_can_idct_4x4())
131 method_ptr = jsimd_idct_4x4;
134 method_ptr = _jpeg_idct_4x4;
135 method = JDCT_ISLOW; /* jidctred uses islow-style table */
138 method_ptr = _jpeg_idct_5x5;
139 method = JDCT_ISLOW; /* jidctint uses islow-style table */
142 #if defined(WITH_SIMD) && defined(__mips__)
143 if (jsimd_can_idct_6x6())
144 method_ptr = jsimd_idct_6x6;
147 method_ptr = _jpeg_idct_6x6;
148 method = JDCT_ISLOW; /* jidctint uses islow-style table */
151 method_ptr = _jpeg_idct_7x7;
152 method = JDCT_ISLOW; /* jidctint uses islow-style table */
156 switch (cinfo->dct_method) {
157 #ifdef DCT_ISLOW_SUPPORTED
160 if (jsimd_can_idct_islow())
161 method_ptr = jsimd_idct_islow;
164 method_ptr = _jpeg_idct_islow;
168 #ifdef DCT_IFAST_SUPPORTED
171 if (jsimd_can_idct_ifast())
172 method_ptr = jsimd_idct_ifast;
175 method_ptr = _jpeg_idct_ifast;
179 #ifdef DCT_FLOAT_SUPPORTED
182 if (jsimd_can_idct_float())
183 method_ptr = jsimd_idct_float;
186 method_ptr = _jpeg_idct_float;
191 ERREXIT(cinfo, JERR_NOT_COMPILED);
195 #ifdef IDCT_SCALING_SUPPORTED
197 method_ptr = _jpeg_idct_9x9;
198 method = JDCT_ISLOW; /* jidctint uses islow-style table */
201 method_ptr = _jpeg_idct_10x10;
202 method = JDCT_ISLOW; /* jidctint uses islow-style table */
205 method_ptr = _jpeg_idct_11x11;
206 method = JDCT_ISLOW; /* jidctint uses islow-style table */
209 #if defined(WITH_SIMD) && defined(__mips__)
210 if (jsimd_can_idct_12x12())
211 method_ptr = jsimd_idct_12x12;
214 method_ptr = _jpeg_idct_12x12;
215 method = JDCT_ISLOW; /* jidctint uses islow-style table */
218 method_ptr = _jpeg_idct_13x13;
219 method = JDCT_ISLOW; /* jidctint uses islow-style table */
222 method_ptr = _jpeg_idct_14x14;
223 method = JDCT_ISLOW; /* jidctint uses islow-style table */
226 method_ptr = _jpeg_idct_15x15;
227 method = JDCT_ISLOW; /* jidctint uses islow-style table */
230 method_ptr = _jpeg_idct_16x16;
231 method = JDCT_ISLOW; /* jidctint uses islow-style table */
235 ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->_DCT_scaled_size);
238 idct->pub._inverse_DCT[ci] = method_ptr;
239 /* Create multiplier table from quant table.
240 * However, we can skip this if the component is uninteresting
241 * or if we already built the table. Also, if no quant table
242 * has yet been saved for the component, we leave the
243 * multiplier table all-zero; we'll be reading zeroes from the
244 * coefficient controller's buffer anyway.
246 if (!compptr->component_needed || idct->cur_method[ci] == method)
248 qtbl = compptr->quant_table;
249 if (qtbl == NULL) /* happens if no data yet for component */
251 idct->cur_method[ci] = method;
253 #ifdef PROVIDE_ISLOW_TABLES
256 /* For LL&M IDCT method, multipliers are equal to raw quantization
257 * coefficients, but are stored as ints to ensure access efficiency.
259 ISLOW_MULT_TYPE *ismtbl = (ISLOW_MULT_TYPE *)compptr->dct_table;
260 for (i = 0; i < DCTSIZE2; i++) {
261 ismtbl[i] = (ISLOW_MULT_TYPE)qtbl->quantval[i];
266 #ifdef DCT_IFAST_SUPPORTED
269 /* For AA&N IDCT method, multipliers are equal to quantization
270 * coefficients scaled by scalefactor[row]*scalefactor[col], where
272 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
273 * For integer operation, the multiplier table is to be scaled by
276 IFAST_MULT_TYPE *ifmtbl = (IFAST_MULT_TYPE *)compptr->dct_table;
277 #define CONST_BITS 14
278 static const INT16 aanscales[DCTSIZE2] = {
279 /* precomputed values scaled up by 14 bits */
280 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
281 22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270,
282 21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906,
283 19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315,
284 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
285 12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552,
286 8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446,
287 4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247
291 for (i = 0; i < DCTSIZE2; i++) {
292 ifmtbl[i] = (IFAST_MULT_TYPE)
293 DESCALE(MULTIPLY16V16((JLONG)qtbl->quantval[i],
294 (JLONG)aanscales[i]),
295 CONST_BITS - IFAST_SCALE_BITS);
300 #ifdef DCT_FLOAT_SUPPORTED
303 /* For float AA&N IDCT method, multipliers are equal to quantization
304 * coefficients scaled by scalefactor[row]*scalefactor[col], where
306 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
308 FLOAT_MULT_TYPE *fmtbl = (FLOAT_MULT_TYPE *)compptr->dct_table;
310 static const double aanscalefactor[DCTSIZE] = {
311 1.0, 1.387039845, 1.306562965, 1.175875602,
312 1.0, 0.785694958, 0.541196100, 0.275899379
316 for (row = 0; row < DCTSIZE; row++) {
317 for (col = 0; col < DCTSIZE; col++) {
318 fmtbl[i] = (FLOAT_MULT_TYPE)
319 ((double)qtbl->quantval[i] *
320 aanscalefactor[row] * aanscalefactor[col]);
328 ERREXIT(cinfo, JERR_NOT_COMPILED);
336 * Initialize IDCT manager.
340 _jinit_inverse_dct(j_decompress_ptr cinfo)
344 jpeg_component_info *compptr;
346 if (cinfo->data_precision != BITS_IN_JSAMPLE)
347 ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);
350 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
351 sizeof(my_idct_controller));
352 cinfo->idct = (struct jpeg_inverse_dct *)idct;
353 idct->pub.start_pass = start_pass;
355 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
357 /* Allocate and pre-zero a multiplier table for each component */
359 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
360 sizeof(multiplier_table));
361 memset(compptr->dct_table, 0, sizeof(multiplier_table));
362 /* Mark multiplier table not yet set up for any method */
363 idct->cur_method[ci] = -1;