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jidctred.c (13528B)
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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 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 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 inptr = coef_block;
136 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
137 wsptr = workspace;
138 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 if (ctr == DCTSIZE-4)
141 continue;
142 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
143 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 &&
144 inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) {
145 /* AC terms all zero; we need not examine term 4 for 4x4 output */
146 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
147
148 wsptr[DCTSIZE*0] = dcval;
149 wsptr[DCTSIZE*1] = dcval;
150 wsptr[DCTSIZE*2] = dcval;
151 wsptr[DCTSIZE*3] = dcval;
152
153 continue;
154 }
155
156 /* Even part */
157
158 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
159 tmp0 <<= (CONST_BITS+1);
160
161 z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
162 z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
163
164 tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
165
166 tmp10 = tmp0 + tmp2;
167 tmp12 = tmp0 - tmp2;
168
169 /* Odd part */
170
171 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
172 z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
173 z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
174 z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
175
176 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
177 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
178 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
179 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
180
181 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
182 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
183 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
184 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
185
186 /* Final output stage */
187
188 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
189 wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
190 wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
191 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 wsptr = workspace;
197 for (ctr = 0; ctr < 4; ctr++) {
198 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 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
203 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
204 /* AC terms all zero */
205 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
206 & RANGE_MASK];
207
208 outptr[0] = dcval;
209 outptr[1] = dcval;
210 outptr[2] = dcval;
211 outptr[3] = dcval;
212
213 wsptr += DCTSIZE; /* advance pointer to next row */
214 continue;
215 }
216 #endif
217
218 /* Even part */
219
220 tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1);
221
222 tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065)
223 + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865);
224
225 tmp10 = tmp0 + tmp2;
226 tmp12 = tmp0 - tmp2;
227
228 /* Odd part */
229
230 z1 = (INT32) wsptr[7];
231 z2 = (INT32) wsptr[5];
232 z3 = (INT32) wsptr[3];
233 z4 = (INT32) wsptr[1];
234
235 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
236 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
237 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
238 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
239
240 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
241 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
242 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
243 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
244
245 /* Final output stage */
246
247 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
248 CONST_BITS+PASS1_BITS+3+1)
249 & RANGE_MASK];
250 outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
251 CONST_BITS+PASS1_BITS+3+1)
252 & RANGE_MASK];
253 outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
254 CONST_BITS+PASS1_BITS+3+1)
255 & RANGE_MASK];
256 outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
257 CONST_BITS+PASS1_BITS+3+1)
258 & RANGE_MASK];
259
260 wsptr += DCTSIZE; /* advance pointer to next row */
261 }
262 }
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 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 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 inptr = coef_block;
288 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
289 wsptr = workspace;
290 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
291 /* Don't bother to process columns 2,4,6 */
292 if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
293 continue;
294 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 &&
295 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 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
298
299 wsptr[DCTSIZE*0] = dcval;
300 wsptr[DCTSIZE*1] = dcval;
301
302 continue;
303 }
304
305 /* Even part */
306
307 z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
308 tmp10 = z1 << (CONST_BITS+2);
309
310 /* Odd part */
311
312 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
313 tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
314 z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
315 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
316 z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
317 tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
318 z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
319 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
320
321 /* Final output stage */
322
323 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
324 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 wsptr = workspace;
330 for (ctr = 0; ctr < 2; ctr++) {
331 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 if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
336 /* AC terms all zero */
337 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
338 & RANGE_MASK];
339
340 outptr[0] = dcval;
341 outptr[1] = dcval;
342
343 wsptr += DCTSIZE; /* advance pointer to next row */
344 continue;
345 }
346 #endif
347
348 /* Even part */
349
350 tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2);
351
352 /* Odd part */
353
354 tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
355 + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
356 + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
357 + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
358
359 /* Final output stage */
360
361 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
362 CONST_BITS+PASS1_BITS+3+2)
363 & RANGE_MASK];
364 outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
365 CONST_BITS+PASS1_BITS+3+2)
366 & RANGE_MASK];
367
368 wsptr += DCTSIZE; /* advance pointer to next row */
369 }
370 }
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 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 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 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
392 dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
393 dcval = (int) DESCALE((INT32) dcval, 3);
394
395 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
396 }
397
398 #endif /* IDCT_SCALING_SUPPORTED */