1 /*
2 * reserved comment block
3 * DO NOT REMOVE OR ALTER!
4 */
5 /*
6 * jidctred.c
7 *
8 * Copyright (C) 1994-1998, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
10 * For conditions of distribution and use, see the accompanying README file.
11 *
12 * This file contains inverse-DCT routines that produce reduced-size output:
13 * either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
14 *
15 * The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
16 * algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step
17 * with an 8-to-4 step that produces the four averages of two adjacent outputs
18 * (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
19 * These steps were derived by computing the corresponding values at the end
20 * of the normal LL&M code, then simplifying as much as possible.
21 *
22 * 1x1 is trivial: just take the DC coefficient divided by 8.
23 *
24 * See jidctint.c for additional comments.
25 */
26
27 #define JPEG_INTERNALS
28 #include "jinclude.h"
29 #include "jpeglib.h"
30 #include "jdct.h" /* Private declarations for DCT subsystem */
31
32 #ifdef IDCT_SCALING_SUPPORTED
33
34
35 /*
36 * This module is specialized to the case DCTSIZE = 8.
37 */
38
39 #if DCTSIZE != 8
40 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
41 #endif
42
43
44 /* Scaling is the same as in jidctint.c. */
45
46 #if BITS_IN_JSAMPLE == 8
47 #define CONST_BITS 13
48 #define PASS1_BITS 2
49 #else
50 #define CONST_BITS 13
51 #define PASS1_BITS 1 /* lose a little precision to avoid overflow */
52 #endif
53
54 /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
55 * causing a lot of useless floating-point operations at run time.
56 * To get around this we use the following pre-calculated constants.
57 * If you change CONST_BITS you may want to add appropriate values.
58 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
59 */
60
61 #if CONST_BITS == 13
62 #define FIX_0_211164243 ((INT32) 1730) /* FIX(0.211164243) */
63 #define FIX_0_509795579 ((INT32) 4176) /* FIX(0.509795579) */
64 #define FIX_0_601344887 ((INT32) 4926) /* FIX(0.601344887) */
65 #define FIX_0_720959822 ((INT32) 5906) /* FIX(0.720959822) */
66 #define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */
67 #define FIX_0_850430095 ((INT32) 6967) /* FIX(0.850430095) */
68 #define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */
69 #define FIX_1_061594337 ((INT32) 8697) /* FIX(1.061594337) */
70 #define FIX_1_272758580 ((INT32) 10426) /* FIX(1.272758580) */
71 #define FIX_1_451774981 ((INT32) 11893) /* FIX(1.451774981) */
72 #define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */
73 #define FIX_2_172734803 ((INT32) 17799) /* FIX(2.172734803) */
74 #define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */
75 #define FIX_3_624509785 ((INT32) 29692) /* FIX(3.624509785) */
76 #else
77 #define FIX_0_211164243 FIX(0.211164243)
78 #define FIX_0_509795579 FIX(0.509795579)
79 #define FIX_0_601344887 FIX(0.601344887)
80 #define FIX_0_720959822 FIX(0.720959822)
81 #define FIX_0_765366865 FIX(0.765366865)
82 #define FIX_0_850430095 FIX(0.850430095)
83 #define FIX_0_899976223 FIX(0.899976223)
84 #define FIX_1_061594337 FIX(1.061594337)
85 #define FIX_1_272758580 FIX(1.272758580)
86 #define FIX_1_451774981 FIX(1.451774981)
87 #define FIX_1_847759065 FIX(1.847759065)
88 #define FIX_2_172734803 FIX(2.172734803)
89 #define FIX_2_562915447 FIX(2.562915447)
90 #define FIX_3_624509785 FIX(3.624509785)
91 #endif
92
93
94 /* Multiply an INT32 variable by an INT32 constant to yield an INT32 result.
95 * For 8-bit samples with the recommended scaling, all the variable
96 * and constant values involved are no more than 16 bits wide, so a
97 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
98 * For 12-bit samples, a full 32-bit multiplication will be needed.
99 */
100
101 #if BITS_IN_JSAMPLE == 8
102 #define MULTIPLY(var,const) MULTIPLY16C16(var,const)
103 #else
104 #define MULTIPLY(var,const) ((var) * (const))
105 #endif
106
107
108 /* Dequantize a coefficient by multiplying it by the multiplier-table
109 * entry; produce an int result. In this module, both inputs and result
110 * are 16 bits or less, so either int or short multiply will work.
111 */
112
113 #define DEQUANTIZE(coef,quantval) (((ISLOW_MULT_TYPE) (coef)) * (quantval))
114
115
116 /*
117 * Perform dequantization and inverse DCT on one block of coefficients,
118 * producing a reduced-size 4x4 output block.
119 */
120
121 GLOBAL(void)
122 jpeg_idct_4x4 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
123 JCOEFPTR coef_block,
124 JSAMPARRAY output_buf, JDIMENSION output_col)
125 {
126 INT32 tmp0, tmp2, tmp10, tmp12;
127 INT32 z1, z2, z3, z4;
128 JCOEFPTR inptr;
129 ISLOW_MULT_TYPE * quantptr;
130 int * wsptr;
131 JSAMPROW outptr;
132 JSAMPLE *range_limit = IDCT_range_limit(cinfo);
133 int ctr;
134 int workspace[DCTSIZE*4]; /* buffers data between passes */
135 SHIFT_TEMPS
136
137 /* Pass 1: process columns from input, store into work array. */
138
139 inptr = coef_block;
140 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
141 wsptr = workspace;
142 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
143 /* Don't bother to process column 4, because second pass won't use it */
144 if (ctr == DCTSIZE-4)
145 continue;
146 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
147 inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*5] == 0 &&
148 inptr[DCTSIZE*6] == 0 && inptr[DCTSIZE*7] == 0) {
149 /* AC terms all zero; we need not examine term 4 for 4x4 output */
150 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
151
152 wsptr[DCTSIZE*0] = dcval;
153 wsptr[DCTSIZE*1] = dcval;
154 wsptr[DCTSIZE*2] = dcval;
155 wsptr[DCTSIZE*3] = dcval;
156
157 continue;
158 }
159
160 /* Even part */
161
162 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
163 tmp0 <<= (CONST_BITS+1);
164
165 z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
166 z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
167
168 tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
169
170 tmp10 = tmp0 + tmp2;
171 tmp12 = tmp0 - tmp2;
172
173 /* Odd part */
174
175 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
176 z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
177 z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
178 z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
179
180 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
181 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
182 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
183 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
184
185 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
186 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
187 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
188 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
189
190 /* Final output stage */
191
192 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
193 wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
194 wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
195 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 wsptr = workspace;
201 for (ctr = 0; ctr < 4; ctr++) {
202 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 if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
207 wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
208 /* AC terms all zero */
209 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
210 & RANGE_MASK];
211
212 outptr[0] = dcval;
213 outptr[1] = dcval;
214 outptr[2] = dcval;
215 outptr[3] = dcval;
216
217 wsptr += DCTSIZE; /* advance pointer to next row */
218 continue;
219 }
220 #endif
221
222 /* Even part */
223
224 tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1);
225
226 tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065)
227 + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865);
228
229 tmp10 = tmp0 + tmp2;
230 tmp12 = tmp0 - tmp2;
231
232 /* Odd part */
233
234 z1 = (INT32) wsptr[7];
235 z2 = (INT32) wsptr[5];
236 z3 = (INT32) wsptr[3];
237 z4 = (INT32) wsptr[1];
238
239 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
240 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
241 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
242 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
243
244 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
245 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
246 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
247 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
248
249 /* Final output stage */
250
251 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
252 CONST_BITS+PASS1_BITS+3+1)
253 & RANGE_MASK];
254 outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
255 CONST_BITS+PASS1_BITS+3+1)
256 & RANGE_MASK];
257 outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
258 CONST_BITS+PASS1_BITS+3+1)
259 & RANGE_MASK];
260 outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
261 CONST_BITS+PASS1_BITS+3+1)
262 & RANGE_MASK];
263
264 wsptr += DCTSIZE; /* advance pointer to next row */
265 }
266 }
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)
jpeg_idct_2x2(j_decompress_ptr cinfo,jpeg_component_info * compptr,JCOEFPTR coef_block,JSAMPARRAY output_buf,JDIMENSION output_col)275 jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
276 JCOEFPTR coef_block,
277 JSAMPARRAY output_buf, JDIMENSION output_col)
278 {
279 INT32 tmp0, tmp10, z1;
280 JCOEFPTR inptr;
281 ISLOW_MULT_TYPE * quantptr;
282 int * wsptr;
283 JSAMPROW outptr;
284 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 inptr = coef_block;
292 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
293 wsptr = workspace;
294 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
295 /* Don't bother to process columns 2,4,6 */
296 if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
297 continue;
298 if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*3] == 0 &&
299 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 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
302
303 wsptr[DCTSIZE*0] = dcval;
304 wsptr[DCTSIZE*1] = dcval;
305
306 continue;
307 }
308
309 /* Even part */
310
311 z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
312 tmp10 = z1 << (CONST_BITS+2);
313
314 /* Odd part */
315
316 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
317 tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
318 z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
319 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
320 z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
321 tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
322 z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
323 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
324
325 /* Final output stage */
326
327 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
328 wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2);
329 }
330
331 /* Pass 2: process 2 rows from work array, store into output array. */
332
333 wsptr = workspace;
334 for (ctr = 0; ctr < 2; ctr++) {
335 outptr = output_buf[ctr] + output_col;
336 /* It's not clear whether a zero row test is worthwhile here ... */
337
338 #ifndef NO_ZERO_ROW_TEST
339 if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
340 /* AC terms all zero */
341 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
342 & RANGE_MASK];
343
344 outptr[0] = dcval;
345 outptr[1] = dcval;
346
347 wsptr += DCTSIZE; /* advance pointer to next row */
348 continue;
349 }
350 #endif
351
352 /* Even part */
353
354 tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2);
355
356 /* Odd part */
357
358 tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
359 + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
360 + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
361 + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
362
363 /* Final output stage */
364
365 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
366 CONST_BITS+PASS1_BITS+3+2)
367 & RANGE_MASK];
368 outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
369 CONST_BITS+PASS1_BITS+3+2)
370 & RANGE_MASK];
371
372 wsptr += DCTSIZE; /* advance pointer to next row */
373 }
374 }
375
376
377 /*
378 * Perform dequantization and inverse DCT on one block of coefficients,
379 * producing a reduced-size 1x1 output block.
380 */
381
382 GLOBAL(void)
jpeg_idct_1x1(j_decompress_ptr cinfo,jpeg_component_info * compptr,JCOEFPTR coef_block,JSAMPARRAY output_buf,JDIMENSION output_col)383 jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
384 JCOEFPTR coef_block,
385 JSAMPARRAY output_buf, JDIMENSION output_col)
386 {
387 int dcval;
388 ISLOW_MULT_TYPE * quantptr;
389 JSAMPLE *range_limit = IDCT_range_limit(cinfo);
390 SHIFT_TEMPS
391
392 /* We hardly need an inverse DCT routine for this: just take the
393 * average pixel value, which is one-eighth of the DC coefficient.
394 */
395 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
396 dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
397 dcval = (int) DESCALE((INT32) dcval, 3);
398
399 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
400 }
401
402 #endif /* IDCT_SCALING_SUPPORTED */
403