1 : /*
2 : * jidctred.c
3 : *
4 : * Copyright (C) 1994-1998, 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 inverse-DCT routines that produce reduced-size output:
9 : * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
10 : *
11 : * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
12 : * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step
13 : * with an 8-to-4 step that produces the four averages of two adjacent outputs
14 : * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
15 : * These steps were derived by computing the corresponding values at the end
16 : * of the normal LL&M code, then simplifying as much as possible.
17 : *
18 : * 1x1 is trivial: just take the DC coefficient divided by 8.
19 : *
20 : * See jidctint.c for additional comments.
21 : */
22 :
23 : #define JPEG_INTERNALS
24 : #include "jinclude.h"
25 : #include "jpeglib.h"
26 : #include "jdct.h" /* Private declarations for DCT subsystem */
27 :
28 : #ifdef IDCT_SCALING_SUPPORTED
29 :
30 :
31 : /*
32 : * This module is specialized to the case DCTSIZE = 8.
33 : */
34 :
35 : #if DCTSIZE != 8
36 : Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
37 : #endif
38 :
39 :
40 : /* Scaling is the same as in jidctint.c. */
41 :
42 : #if BITS_IN_JSAMPLE == 8
43 : #define CONST_BITS 13
44 : #define PASS1_BITS 2
45 : #else
46 : #define CONST_BITS 13
47 : #define PASS1_BITS 1 /* lose a little precision to avoid overflow */
48 : #endif
49 :
50 : /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
51 : * causing a lot of useless floating-point operations at run time.
52 : * To get around this we use the following pre-calculated constants.
53 : * If you change CONST_BITS you may want to add appropriate values.
54 : * (With a reasonable C compiler, you can just rely on the FIX() macro...)
55 : */
56 :
57 : #if CONST_BITS == 13
58 : #define FIX_0_211164243 ((INT32) 1730) /* FIX(0.211164243) */
59 : #define FIX_0_509795579 ((INT32) 4176) /* FIX(0.509795579) */
60 : #define FIX_0_601344887 ((INT32) 4926) /* FIX(0.601344887) */
61 : #define FIX_0_720959822 ((INT32) 5906) /* FIX(0.720959822) */
62 : #define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */
63 : #define FIX_0_850430095 ((INT32) 6967) /* FIX(0.850430095) */
64 : #define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */
65 : #define FIX_1_061594337 ((INT32) 8697) /* FIX(1.061594337) */
66 : #define FIX_1_272758580 ((INT32) 10426) /* FIX(1.272758580) */
67 : #define FIX_1_451774981 ((INT32) 11893) /* FIX(1.451774981) */
68 : #define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */
69 : #define FIX_2_172734803 ((INT32) 17799) /* FIX(2.172734803) */
70 : #define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */
71 : #define FIX_3_624509785 ((INT32) 29692) /* FIX(3.624509785) */
72 : #else
73 : #define FIX_0_211164243 FIX(0.211164243)
74 : #define FIX_0_509795579 FIX(0.509795579)
75 : #define FIX_0_601344887 FIX(0.601344887)
76 : #define FIX_0_720959822 FIX(0.720959822)
77 : #define FIX_0_765366865 FIX(0.765366865)
78 : #define FIX_0_850430095 FIX(0.850430095)
79 : #define FIX_0_899976223 FIX(0.899976223)
80 : #define FIX_1_061594337 FIX(1.061594337)
81 : #define FIX_1_272758580 FIX(1.272758580)
82 : #define FIX_1_451774981 FIX(1.451774981)
83 : #define FIX_1_847759065 FIX(1.847759065)
84 : #define FIX_2_172734803 FIX(2.172734803)
85 : #define FIX_2_562915447 FIX(2.562915447)
86 : #define FIX_3_624509785 FIX(3.624509785)
87 : #endif
88 :
89 :
90 : /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
91 : * For 8-bit samples with the recommended scaling, all the variable
92 : * and constant values involved are no more than 16 bits wide, so a
93 : * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
94 : * For 12-bit samples, a full 32-bit multiplication will be needed.
95 : */
96 :
97 : #if BITS_IN_JSAMPLE == 8
98 : #define MULTIPLY(var,const) MULTIPLY16C16(var,const)
99 : #else
100 : #define MULTIPLY(var,const) ((var) * (const))
101 : #endif
102 :
103 :
104 : /* Dequantize a coefficient by multiplying it by the multiplier-table
105 : * entry; produce an int result. In this module, both inputs and result
106 : * are 16 bits or less, so either int or short multiply will work.
107 : */
108 :
109 : #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval))
110 :
111 :
112 : /*
113 : * Perform dequantization and inverse DCT on one block of coefficients,
114 : * producing a reduced-size 4x4 output block.
115 : */
116 :
117 : GLOBAL(void)
118 0 : jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
119 : JCOEFPTR coef_block,
120 : JSAMPARRAY output_buf, JDIMENSION output_col)
121 : {
122 : INT32 tmp0, tmp2, tmp10, tmp12;
123 : INT32 z1, z2, z3, z4;
124 : JCOEFPTR inptr;
125 : ISLOW_MULT_TYPE * quantptr;
126 : int * wsptr;
127 : JSAMPROW outptr;
128 0 : JSAMPLE *range_limit = IDCT_range_limit(cinfo);
129 : int ctr;
130 : int workspace[DCTSIZE*4]; /* buffers data between passes */
131 : SHIFT_TEMPS
132 :
133 : /* Pass 1: process columns from input, store into work array. */
134 :
135 0 : inptr = coef_block;
136 0 : quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
137 0 : wsptr = workspace;
138 0 : for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
139 : /* Don't bother to process column 4, because second pass won't use it */
140 0 : if (ctr == DCTSIZE-4)
141 0 : continue;
142 0 : if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
143 0 : inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 &&
144 0 : inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) {
145 : /* AC terms all zero; we need not examine term 4 for 4x4 output */
146 0 : int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
147 :
148 0 : wsptr[DCTSIZE*0] = dcval;
149 0 : wsptr[DCTSIZE*1] = dcval;
150 0 : wsptr[DCTSIZE*2] = dcval;
151 0 : wsptr[DCTSIZE*3] = dcval;
152 :
153 0 : continue;
154 : }
155 :
156 : /* Even part */
157 :
158 0 : tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
159 0 : tmp0 <<= (CONST_BITS+1);
160 :
161 0 : z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
162 0 : z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
163 :
164 0 : tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
165 :
166 0 : tmp10 = tmp0 + tmp2;
167 0 : tmp12 = tmp0 - tmp2;
168 :
169 : /* Odd part */
170 :
171 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
172 0 : z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
173 0 : z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
174 0 : z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
175 :
176 0 : tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
177 0 : + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
178 0 : + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
179 0 : + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
180 :
181 0 : tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
182 0 : + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
183 0 : + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
184 0 : + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
185 :
186 : /* Final output stage */
187 :
188 0 : wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
189 0 : wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
190 0 : wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
191 0 : wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1);
192 : }
193 :
194 : /* Pass 2: process 4 rows from work array, store into output array. */
195 :
196 0 : wsptr = workspace;
197 0 : for (ctr = 0; ctr < 4; ctr++) {
198 0 : outptr = output_buf[ctr] + output_col;
199 : /* It's not clear whether a zero row test is worthwhile here ... */
200 :
201 : #ifndef NO_ZERO_ROW_TEST
202 0 : if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
203 0 : wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
204 : /* AC terms all zero */
205 0 : JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
206 : & RANGE_MASK];
207 :
208 0 : outptr[0] = dcval;
209 0 : outptr[1] = dcval;
210 0 : outptr[2] = dcval;
211 0 : outptr[3] = dcval;
212 :
213 0 : wsptr += DCTSIZE; /* advance pointer to next row */
214 0 : continue;
215 : }
216 : #endif
217 :
218 : /* Even part */
219 :
220 0 : tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1);
221 :
222 0 : tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065)
223 0 : + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865);
224 :
225 0 : tmp10 = tmp0 + tmp2;
226 0 : tmp12 = tmp0 - tmp2;
227 :
228 : /* Odd part */
229 :
230 0 : z1 = (INT32) wsptr[7];
231 0 : z2 = (INT32) wsptr[5];
232 0 : z3 = (INT32) wsptr[3];
233 0 : z4 = (INT32) wsptr[1];
234 :
235 0 : tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
236 0 : + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
237 0 : + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
238 0 : + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
239 :
240 0 : tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
241 0 : + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
242 0 : + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
243 0 : + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
244 :
245 : /* Final output stage */
246 :
247 0 : outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
248 : CONST_BITS+PASS1_BITS+3+1)
249 : & RANGE_MASK];
250 0 : outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
251 : CONST_BITS+PASS1_BITS+3+1)
252 : & RANGE_MASK];
253 0 : outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
254 : CONST_BITS+PASS1_BITS+3+1)
255 : & RANGE_MASK];
256 0 : outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
257 : CONST_BITS+PASS1_BITS+3+1)
258 : & RANGE_MASK];
259 :
260 0 : wsptr += DCTSIZE; /* advance pointer to next row */
261 : }
262 0 : }
263 :
264 :
265 : /*
266 : * Perform dequantization and inverse DCT on one block of coefficients,
267 : * producing a reduced-size 2x2 output block.
268 : */
269 :
270 : GLOBAL(void)
271 0 : jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
272 : JCOEFPTR coef_block,
273 : JSAMPARRAY output_buf, JDIMENSION output_col)
274 : {
275 : INT32 tmp0, tmp10, z1;
276 : JCOEFPTR inptr;
277 : ISLOW_MULT_TYPE * quantptr;
278 : int * wsptr;
279 : JSAMPROW outptr;
280 0 : JSAMPLE *range_limit = IDCT_range_limit(cinfo);
281 : int ctr;
282 : int workspace[DCTSIZE*2]; /* buffers data between passes */
283 : SHIFT_TEMPS
284 :
285 : /* Pass 1: process columns from input, store into work array. */
286 :
287 0 : inptr = coef_block;
288 0 : quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
289 0 : wsptr = workspace;
290 0 : for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
291 : /* Don't bother to process columns 2,4,6 */
292 0 : if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
293 0 : continue;
294 0 : if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 &&
295 0 : inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) {
296 : /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
297 0 : int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
298 :
299 0 : wsptr[DCTSIZE*0] = dcval;
300 0 : wsptr[DCTSIZE*1] = dcval;
301 :
302 0 : continue;
303 : }
304 :
305 : /* Even part */
306 :
307 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
308 0 : tmp10 = z1 << (CONST_BITS+2);
309 :
310 : /* Odd part */
311 :
312 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
313 0 : tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
314 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
315 0 : tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
316 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
317 0 : tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
318 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
319 0 : tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
320 :
321 : /* Final output stage */
322 :
323 0 : wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
324 0 : wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2);
325 : }
326 :
327 : /* Pass 2: process 2 rows from work array, store into output array. */
328 :
329 0 : wsptr = workspace;
330 0 : for (ctr = 0; ctr < 2; ctr++) {
331 0 : outptr = output_buf[ctr] + output_col;
332 : /* It's not clear whether a zero row test is worthwhile here ... */
333 :
334 : #ifndef NO_ZERO_ROW_TEST
335 0 : if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
336 : /* AC terms all zero */
337 0 : JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
338 : & RANGE_MASK];
339 :
340 0 : outptr[0] = dcval;
341 0 : outptr[1] = dcval;
342 :
343 0 : wsptr += DCTSIZE; /* advance pointer to next row */
344 0 : continue;
345 : }
346 : #endif
347 :
348 : /* Even part */
349 :
350 0 : tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2);
351 :
352 : /* Odd part */
353 :
354 0 : tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
355 0 : + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
356 0 : + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
357 0 : + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
358 :
359 : /* Final output stage */
360 :
361 0 : outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
362 : CONST_BITS+PASS1_BITS+3+2)
363 : & RANGE_MASK];
364 0 : outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
365 : CONST_BITS+PASS1_BITS+3+2)
366 : & RANGE_MASK];
367 :
368 0 : wsptr += DCTSIZE; /* advance pointer to next row */
369 : }
370 0 : }
371 :
372 :
373 : /*
374 : * Perform dequantization and inverse DCT on one block of coefficients,
375 : * producing a reduced-size 1x1 output block.
376 : */
377 :
378 : GLOBAL(void)
379 0 : jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
380 : JCOEFPTR coef_block,
381 : JSAMPARRAY output_buf, JDIMENSION output_col)
382 : {
383 : int dcval;
384 : ISLOW_MULT_TYPE * quantptr;
385 0 : JSAMPLE *range_limit = IDCT_range_limit(cinfo);
386 : SHIFT_TEMPS
387 :
388 : /* We hardly need an inverse DCT routine for this: just take the
389 : * average pixel value, which is one-eighth of the DC coefficient.
390 : */
391 0 : quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
392 0 : dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
393 0 : dcval = (int) DESCALE((INT32) dcval, 3);
394 :
395 0 : output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
396 0 : }
397 :
398 : #endif /* IDCT_SCALING_SUPPORTED */
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