4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
6 * Copyright (C) 2010, D. R. Commander.
7 * This file is part of the Independent JPEG Group's software.
8 * For conditions of distribution and use, see the accompanying README file.
10 * This file contains the inverse-DCT management logic.
11 * This code selects a particular IDCT implementation to be used,
12 * and it performs related housekeeping chores. No code in this file
13 * is executed per IDCT step, only during output pass setup.
15 * Note that the IDCT routines are responsible for performing coefficient
16 * dequantization as well as the IDCT proper. This module sets up the
17 * dequantization multiplier table needed by the IDCT routine.
20 #define JPEG_INTERNALS
23 #include "jdct.h" /* Private declarations for DCT subsystem */
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.
45 /* Private subobject for this module */
48 struct jpeg_inverse_dct pub; /* public fields */
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.
55 int cur_method[MAX_COMPONENTS];
58 typedef my_idct_controller * my_idct_ptr;
61 /* Allocated multiplier tables: big enough for any supported variant */
64 ISLOW_MULT_TYPE islow_array[DCTSIZE2];
65 #ifdef DCT_IFAST_SUPPORTED
66 IFAST_MULT_TYPE ifast_array[DCTSIZE2];
68 #ifdef DCT_FLOAT_SUPPORTED
69 FLOAT_MULT_TYPE float_array[DCTSIZE2];
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.
77 #ifdef DCT_ISLOW_SUPPORTED
78 #define PROVIDE_ISLOW_TABLES
80 #ifdef IDCT_SCALING_SUPPORTED
81 #define PROVIDE_ISLOW_TABLES
87 * Prepare for an output pass.
88 * Here we select the proper IDCT routine for each component and build
89 * a matching multiplier table.
93 start_pass (j_decompress_ptr cinfo)
95 my_idct_ptr idct = (my_idct_ptr) cinfo->idct;
97 jpeg_component_info *compptr;
99 inverse_DCT_method_ptr method_ptr = NULL;
102 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
104 /* Select the proper IDCT routine for this component's scaling */
105 switch (compptr->_DCT_scaled_size) {
106 #ifdef IDCT_SCALING_SUPPORTED
108 method_ptr = jpeg_idct_1x1;
109 method = JDCT_ISLOW; /* jidctred uses islow-style table */
112 if (jsimd_can_idct_2x2())
113 method_ptr = jsimd_idct_2x2;
115 method_ptr = jpeg_idct_2x2;
116 method = JDCT_ISLOW; /* jidctred uses islow-style table */
119 if (jsimd_can_idct_4x4())
120 method_ptr = jsimd_idct_4x4;
122 method_ptr = jpeg_idct_4x4;
123 method = JDCT_ISLOW; /* jidctred uses islow-style table */
127 switch (cinfo->dct_method) {
128 #ifdef DCT_ISLOW_SUPPORTED
130 if (jsimd_can_idct_islow())
131 method_ptr = jsimd_idct_islow;
133 method_ptr = jpeg_idct_islow;
137 #ifdef DCT_IFAST_SUPPORTED
139 if (jsimd_can_idct_ifast())
140 method_ptr = jsimd_idct_ifast;
142 method_ptr = jpeg_idct_ifast;
146 #ifdef DCT_FLOAT_SUPPORTED
148 if (jsimd_can_idct_float())
149 method_ptr = jsimd_idct_float;
151 method_ptr = jpeg_idct_float;
156 ERREXIT(cinfo, JERR_NOT_COMPILED);
161 ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->_DCT_scaled_size);
164 idct->pub.inverse_DCT[ci] = method_ptr;
165 /* Create multiplier table from quant table.
166 * However, we can skip this if the component is uninteresting
167 * or if we already built the table. Also, if no quant table
168 * has yet been saved for the component, we leave the
169 * multiplier table all-zero; we'll be reading zeroes from the
170 * coefficient controller's buffer anyway.
172 if (! compptr->component_needed || idct->cur_method[ci] == method)
174 qtbl = compptr->quant_table;
175 if (qtbl == NULL) /* happens if no data yet for component */
177 idct->cur_method[ci] = method;
179 #ifdef PROVIDE_ISLOW_TABLES
182 /* For LL&M IDCT method, multipliers are equal to raw quantization
183 * coefficients, but are stored as ints to ensure access efficiency.
185 ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
186 for (i = 0; i < DCTSIZE2; i++) {
187 ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[i];
192 #ifdef DCT_IFAST_SUPPORTED
195 /* For AA&N IDCT method, multipliers are equal to quantization
196 * coefficients scaled by scalefactor[row]*scalefactor[col], where
198 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
199 * For integer operation, the multiplier table is to be scaled by
202 IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table;
203 #define CONST_BITS 14
204 static const INT16 aanscales[DCTSIZE2] = {
205 /* precomputed values scaled up by 14 bits */
206 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
207 22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270,
208 21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906,
209 19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315,
210 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520,
211 12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552,
212 8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446,
213 4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247
217 for (i = 0; i < DCTSIZE2; i++) {
218 ifmtbl[i] = (IFAST_MULT_TYPE)
219 DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i],
220 (INT32) aanscales[i]),
221 CONST_BITS-IFAST_SCALE_BITS);
226 #ifdef DCT_FLOAT_SUPPORTED
229 /* For float AA&N IDCT method, multipliers are equal to quantization
230 * coefficients scaled by scalefactor[row]*scalefactor[col], where
232 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
234 FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table;
236 static const double aanscalefactor[DCTSIZE] = {
237 1.0, 1.387039845, 1.306562965, 1.175875602,
238 1.0, 0.785694958, 0.541196100, 0.275899379
242 for (row = 0; row < DCTSIZE; row++) {
243 for (col = 0; col < DCTSIZE; col++) {
244 fmtbl[i] = (FLOAT_MULT_TYPE)
245 ((double) qtbl->quantval[i] *
246 aanscalefactor[row] * aanscalefactor[col]);
254 ERREXIT(cinfo, JERR_NOT_COMPILED);
262 * Initialize IDCT manager.
266 jinit_inverse_dct (j_decompress_ptr cinfo)
270 jpeg_component_info *compptr;
273 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
274 SIZEOF(my_idct_controller));
275 cinfo->idct = (struct jpeg_inverse_dct *) idct;
276 idct->pub.start_pass = start_pass;
278 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
280 /* Allocate and pre-zero a multiplier table for each component */
282 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
283 SIZEOF(multiplier_table));
284 MEMZERO(compptr->dct_table, SIZEOF(multiplier_table));
285 /* Mark multiplier table not yet set up for any method */
286 idct->cur_method[ci] = -1;