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)
start_pass(j_decompress_ptr cinfo)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)
jinit_inverse_dct(j_decompress_ptr cinfo)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 }
270