Line data Source code
1 : /*
2 : * jidctred.c
3 : *
4 : * This file was part of the Independent JPEG Group's software.
5 : * Copyright (C) 1994-1998, Thomas G. Lane.
6 : * libjpeg-turbo Modifications:
7 : * Copyright (C) 2015, D. R. Commander.
8 : * For conditions of distribution and use, see the accompanying README.ijg
9 : * file.
10 : *
11 : * This file contains inverse-DCT routines that produce reduced-size output:
12 : * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
13 : *
14 : * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
15 : * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step
16 : * with an 8-to-4 step that produces the four averages of two adjacent outputs
17 : * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
18 : * These steps were derived by computing the corresponding values at the end
19 : * of the normal LL&M code, then simplifying as much as possible.
20 : *
21 : * 1x1 is trivial: just take the DC coefficient divided by 8.
22 : *
23 : * See jidctint.c for additional comments.
24 : */
25 :
26 : #define JPEG_INTERNALS
27 : #include "jinclude.h"
28 : #include "jpeglib.h"
29 : #include "jdct.h" /* Private declarations for DCT subsystem */
30 :
31 : #ifdef IDCT_SCALING_SUPPORTED
32 :
33 :
34 : /*
35 : * This module is specialized to the case DCTSIZE = 8.
36 : */
37 :
38 : #if DCTSIZE != 8
39 : Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
40 : #endif
41 :
42 :
43 : /* Scaling is the same as in jidctint.c. */
44 :
45 : #if BITS_IN_JSAMPLE == 8
46 : #define CONST_BITS 13
47 : #define PASS1_BITS 2
48 : #else
49 : #define CONST_BITS 13
50 : #define PASS1_BITS 1 /* lose a little precision to avoid overflow */
51 : #endif
52 :
53 : /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
54 : * causing a lot of useless floating-point operations at run time.
55 : * To get around this we use the following pre-calculated constants.
56 : * If you change CONST_BITS you may want to add appropriate values.
57 : * (With a reasonable C compiler, you can just rely on the FIX() macro...)
58 : */
59 :
60 : #if CONST_BITS == 13
61 : #define FIX_0_211164243 ((JLONG) 1730) /* FIX(0.211164243) */
62 : #define FIX_0_509795579 ((JLONG) 4176) /* FIX(0.509795579) */
63 : #define FIX_0_601344887 ((JLONG) 4926) /* FIX(0.601344887) */
64 : #define FIX_0_720959822 ((JLONG) 5906) /* FIX(0.720959822) */
65 : #define FIX_0_765366865 ((JLONG) 6270) /* FIX(0.765366865) */
66 : #define FIX_0_850430095 ((JLONG) 6967) /* FIX(0.850430095) */
67 : #define FIX_0_899976223 ((JLONG) 7373) /* FIX(0.899976223) */
68 : #define FIX_1_061594337 ((JLONG) 8697) /* FIX(1.061594337) */
69 : #define FIX_1_272758580 ((JLONG) 10426) /* FIX(1.272758580) */
70 : #define FIX_1_451774981 ((JLONG) 11893) /* FIX(1.451774981) */
71 : #define FIX_1_847759065 ((JLONG) 15137) /* FIX(1.847759065) */
72 : #define FIX_2_172734803 ((JLONG) 17799) /* FIX(2.172734803) */
73 : #define FIX_2_562915447 ((JLONG) 20995) /* FIX(2.562915447) */
74 : #define FIX_3_624509785 ((JLONG) 29692) /* FIX(3.624509785) */
75 : #else
76 : #define FIX_0_211164243 FIX(0.211164243)
77 : #define FIX_0_509795579 FIX(0.509795579)
78 : #define FIX_0_601344887 FIX(0.601344887)
79 : #define FIX_0_720959822 FIX(0.720959822)
80 : #define FIX_0_765366865 FIX(0.765366865)
81 : #define FIX_0_850430095 FIX(0.850430095)
82 : #define FIX_0_899976223 FIX(0.899976223)
83 : #define FIX_1_061594337 FIX(1.061594337)
84 : #define FIX_1_272758580 FIX(1.272758580)
85 : #define FIX_1_451774981 FIX(1.451774981)
86 : #define FIX_1_847759065 FIX(1.847759065)
87 : #define FIX_2_172734803 FIX(2.172734803)
88 : #define FIX_2_562915447 FIX(2.562915447)
89 : #define FIX_3_624509785 FIX(3.624509785)
90 : #endif
91 :
92 :
93 : /* Multiply a JLONG variable by a JLONG constant to yield a JLONG result.
94 : * For 8-bit samples with the recommended scaling, all the variable
95 : * and constant values involved are no more than 16 bits wide, so a
96 : * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
97 : * For 12-bit samples, a full 32-bit multiplication will be needed.
98 : */
99 :
100 : #if BITS_IN_JSAMPLE == 8
101 : #define MULTIPLY(var,const) MULTIPLY16C16(var,const)
102 : #else
103 : #define MULTIPLY(var,const) ((var) * (const))
104 : #endif
105 :
106 :
107 : /* Dequantize a coefficient by multiplying it by the multiplier-table
108 : * entry; produce an int result. In this module, both inputs and result
109 : * are 16 bits or less, so either int or short multiply will work.
110 : */
111 :
112 : #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval))
113 :
114 :
115 : /*
116 : * Perform dequantization and inverse DCT on one block of coefficients,
117 : * producing a reduced-size 4x4 output block.
118 : */
119 :
120 : GLOBAL(void)
121 0 : jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info *compptr,
122 : JCOEFPTR coef_block,
123 : JSAMPARRAY output_buf, JDIMENSION output_col)
124 : {
125 : JLONG tmp0, tmp2, tmp10, tmp12;
126 : JLONG z1, z2, z3, z4;
127 : JCOEFPTR inptr;
128 : ISLOW_MULT_TYPE *quantptr;
129 : int *wsptr;
130 : JSAMPROW outptr;
131 0 : JSAMPLE *range_limit = IDCT_range_limit(cinfo);
132 : int ctr;
133 : int workspace[DCTSIZE*4]; /* buffers data between passes */
134 : SHIFT_TEMPS
135 :
136 : /* Pass 1: process columns from input, store into work array. */
137 :
138 0 : inptr = coef_block;
139 0 : quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
140 0 : wsptr = workspace;
141 0 : for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
142 : /* Don't bother to process column 4, because second pass won't use it */
143 0 : if (ctr == DCTSIZE-4)
144 0 : continue;
145 0 : if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
146 0 : inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 &&
147 0 : inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) {
148 : /* AC terms all zero; we need not examine term 4 for 4x4 output */
149 0 : int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]),
150 : PASS1_BITS);
151 :
152 0 : wsptr[DCTSIZE*0] = dcval;
153 0 : wsptr[DCTSIZE*1] = dcval;
154 0 : wsptr[DCTSIZE*2] = dcval;
155 0 : wsptr[DCTSIZE*3] = dcval;
156 :
157 0 : continue;
158 : }
159 :
160 : /* Even part */
161 :
162 0 : tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
163 0 : tmp0 = LEFT_SHIFT(tmp0, CONST_BITS+1);
164 :
165 0 : z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
166 0 : z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
167 :
168 0 : tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
169 :
170 0 : tmp10 = tmp0 + tmp2;
171 0 : tmp12 = tmp0 - tmp2;
172 :
173 : /* Odd part */
174 :
175 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
176 0 : z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
177 0 : z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
178 0 : z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
179 :
180 0 : tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
181 0 : + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
182 0 : + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
183 0 : + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
184 :
185 0 : tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
186 0 : + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
187 0 : + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
188 0 : + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
189 :
190 : /* Final output stage */
191 :
192 0 : wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
193 0 : wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
194 0 : wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
195 0 : wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1);
196 : }
197 :
198 : /* Pass 2: process 4 rows from work array, store into output array. */
199 :
200 0 : wsptr = workspace;
201 0 : for (ctr = 0; ctr < 4; ctr++) {
202 0 : outptr = output_buf[ctr] + output_col;
203 : /* It's not clear whether a zero row test is worthwhile here ... */
204 :
205 : #ifndef NO_ZERO_ROW_TEST
206 0 : if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
207 0 : wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
208 : /* AC terms all zero */
209 0 : JSAMPLE dcval = range_limit[(int) DESCALE((JLONG) wsptr[0], PASS1_BITS+3)
210 0 : & RANGE_MASK];
211 :
212 0 : outptr[0] = dcval;
213 0 : outptr[1] = dcval;
214 0 : outptr[2] = dcval;
215 0 : outptr[3] = dcval;
216 :
217 0 : wsptr += DCTSIZE; /* advance pointer to next row */
218 0 : continue;
219 : }
220 : #endif
221 :
222 : /* Even part */
223 :
224 0 : tmp0 = LEFT_SHIFT((JLONG) wsptr[0], CONST_BITS+1);
225 :
226 0 : tmp2 = MULTIPLY((JLONG) wsptr[2], FIX_1_847759065)
227 0 : + MULTIPLY((JLONG) wsptr[6], - FIX_0_765366865);
228 :
229 0 : tmp10 = tmp0 + tmp2;
230 0 : tmp12 = tmp0 - tmp2;
231 :
232 : /* Odd part */
233 :
234 0 : z1 = (JLONG) wsptr[7];
235 0 : z2 = (JLONG) wsptr[5];
236 0 : z3 = (JLONG) wsptr[3];
237 0 : z4 = (JLONG) wsptr[1];
238 :
239 0 : tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
240 0 : + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
241 0 : + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
242 0 : + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
243 :
244 0 : tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
245 0 : + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
246 0 : + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
247 0 : + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
248 :
249 : /* Final output stage */
250 :
251 0 : outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
252 : CONST_BITS+PASS1_BITS+3+1)
253 0 : & RANGE_MASK];
254 0 : outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
255 : CONST_BITS+PASS1_BITS+3+1)
256 0 : & RANGE_MASK];
257 0 : outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
258 : CONST_BITS+PASS1_BITS+3+1)
259 0 : & RANGE_MASK];
260 0 : outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
261 : CONST_BITS+PASS1_BITS+3+1)
262 0 : & RANGE_MASK];
263 :
264 0 : wsptr += DCTSIZE; /* advance pointer to next row */
265 : }
266 0 : }
267 :
268 :
269 : /*
270 : * Perform dequantization and inverse DCT on one block of coefficients,
271 : * producing a reduced-size 2x2 output block.
272 : */
273 :
274 : GLOBAL(void)
275 0 : jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info *compptr,
276 : JCOEFPTR coef_block,
277 : JSAMPARRAY output_buf, JDIMENSION output_col)
278 : {
279 : JLONG tmp0, tmp10, z1;
280 : JCOEFPTR inptr;
281 : ISLOW_MULT_TYPE *quantptr;
282 : int *wsptr;
283 : JSAMPROW outptr;
284 0 : JSAMPLE *range_limit = IDCT_range_limit(cinfo);
285 : int ctr;
286 : int workspace[DCTSIZE*2]; /* buffers data between passes */
287 : SHIFT_TEMPS
288 :
289 : /* Pass 1: process columns from input, store into work array. */
290 :
291 0 : inptr = coef_block;
292 0 : quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
293 0 : wsptr = workspace;
294 0 : for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
295 : /* Don't bother to process columns 2,4,6 */
296 0 : if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
297 0 : continue;
298 0 : if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 &&
299 0 : inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*7] == 0) {
300 : /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
301 0 : int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]),
302 : PASS1_BITS);
303 :
304 0 : wsptr[DCTSIZE*0] = dcval;
305 0 : wsptr[DCTSIZE*1] = dcval;
306 :
307 0 : continue;
308 : }
309 :
310 : /* Even part */
311 :
312 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
313 0 : tmp10 = LEFT_SHIFT(z1, CONST_BITS+2);
314 :
315 : /* Odd part */
316 :
317 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
318 0 : tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
319 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
320 0 : tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
321 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
322 0 : tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
323 0 : z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
324 0 : tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
325 :
326 : /* Final output stage */
327 :
328 0 : wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
329 0 : wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2);
330 : }
331 :
332 : /* Pass 2: process 2 rows from work array, store into output array. */
333 :
334 0 : wsptr = workspace;
335 0 : for (ctr = 0; ctr < 2; ctr++) {
336 0 : outptr = output_buf[ctr] + output_col;
337 : /* It's not clear whether a zero row test is worthwhile here ... */
338 :
339 : #ifndef NO_ZERO_ROW_TEST
340 0 : if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
341 : /* AC terms all zero */
342 0 : JSAMPLE dcval = range_limit[(int) DESCALE((JLONG) wsptr[0], PASS1_BITS+3)
343 0 : & RANGE_MASK];
344 :
345 0 : outptr[0] = dcval;
346 0 : outptr[1] = dcval;
347 :
348 0 : wsptr += DCTSIZE; /* advance pointer to next row */
349 0 : continue;
350 : }
351 : #endif
352 :
353 : /* Even part */
354 :
355 0 : tmp10 = LEFT_SHIFT((JLONG) wsptr[0], CONST_BITS+2);
356 :
357 : /* Odd part */
358 :
359 0 : tmp0 = MULTIPLY((JLONG) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
360 0 : + MULTIPLY((JLONG) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
361 0 : + MULTIPLY((JLONG) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
362 0 : + MULTIPLY((JLONG) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
363 :
364 : /* Final output stage */
365 :
366 0 : outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
367 : CONST_BITS+PASS1_BITS+3+2)
368 0 : & RANGE_MASK];
369 0 : outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
370 : CONST_BITS+PASS1_BITS+3+2)
371 0 : & RANGE_MASK];
372 :
373 0 : wsptr += DCTSIZE; /* advance pointer to next row */
374 : }
375 0 : }
376 :
377 :
378 : /*
379 : * Perform dequantization and inverse DCT on one block of coefficients,
380 : * producing a reduced-size 1x1 output block.
381 : */
382 :
383 : GLOBAL(void)
384 0 : jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info *compptr,
385 : JCOEFPTR coef_block,
386 : JSAMPARRAY output_buf, JDIMENSION output_col)
387 : {
388 : int dcval;
389 : ISLOW_MULT_TYPE *quantptr;
390 0 : JSAMPLE *range_limit = IDCT_range_limit(cinfo);
391 : SHIFT_TEMPS
392 :
393 : /* We hardly need an inverse DCT routine for this: just take the
394 : * average pixel value, which is one-eighth of the DC coefficient.
395 : */
396 0 : quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
397 0 : dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
398 0 : dcval = (int) DESCALE((JLONG) dcval, 3);
399 :
400 0 : output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
401 0 : }
402 :
403 : #endif /* IDCT_SCALING_SUPPORTED */
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