1 /*
2 * jidctred.c
3 *
4 * Copyright (C) 1994, 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] | inptr[DCTSIZE*2] | inptr[DCTSIZE*3] |
143 inptr[DCTSIZE*5] | inptr[DCTSIZE*6] | inptr[DCTSIZE*7]) == 0) {
144 /* AC terms all zero; we need not examine term 4 for 4x4 output */
145 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
146
147 wsptr[DCTSIZE*0] = dcval;
148 wsptr[DCTSIZE*1] = dcval;
149 wsptr[DCTSIZE*2] = dcval;
150 wsptr[DCTSIZE*3] = dcval;
151
152 continue;
153 }
154
155 /* Even part */
156
157 tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
158 tmp0 <<= (CONST_BITS+1);
159
160 z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
161 z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
162
163 tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, - FIX_0_765366865);
164
165 tmp10 = tmp0 + tmp2;
166 tmp12 = tmp0 - tmp2;
167
168 /* Odd part */
169
170 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
171 z2 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
172 z3 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
173 z4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
174
175 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
176 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
177 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
178 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
179
180 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
181 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
182 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
183 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
184
185 /* Final output stage */
186
187 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp2, CONST_BITS-PASS1_BITS+1);
188 wsptr[DCTSIZE*3] = (int) DESCALE(tmp10 - tmp2, CONST_BITS-PASS1_BITS+1);
189 wsptr[DCTSIZE*1] = (int) DESCALE(tmp12 + tmp0, CONST_BITS-PASS1_BITS+1);
190 wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 - tmp0, CONST_BITS-PASS1_BITS+1);
191 }
192
193 /* Pass 2: process 4 rows from work array, store into output array. */
194
195 wsptr = workspace;
196 for (ctr = 0; ctr < 4; ctr++) {
197 outptr = output_buf[ctr] + output_col;
198 /* It's not clear whether a zero row test is worthwhile here ... */
199
200 #ifndef NO_ZERO_ROW_TEST
201 if ((wsptr[1] | wsptr[2] | wsptr[3] | wsptr[5] | wsptr[6] |
202 wsptr[7]) == 0) {
203 /* AC terms all zero */
204 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
205 & RANGE_MASK];
206
207 outptr[0] = dcval;
208 outptr[1] = dcval;
209 outptr[2] = dcval;
210 outptr[3] = dcval;
211
212 wsptr += DCTSIZE; /* advance pointer to next row */
213 continue;
214 }
215 #endif
216
217 /* Even part */
218
219 tmp0 = ((INT32) wsptr[0]) << (CONST_BITS+1);
220
221 tmp2 = MULTIPLY((INT32) wsptr[2], FIX_1_847759065)
222 + MULTIPLY((INT32) wsptr[6], - FIX_0_765366865);
223
224 tmp10 = tmp0 + tmp2;
225 tmp12 = tmp0 - tmp2;
226
227 /* Odd part */
228
229 z1 = (INT32) wsptr[7];
230 z2 = (INT32) wsptr[5];
231 z3 = (INT32) wsptr[3];
232 z4 = (INT32) wsptr[1];
233
234 tmp0 = MULTIPLY(z1, - FIX_0_211164243) /* sqrt(2) * (c3-c1) */
235 + MULTIPLY(z2, FIX_1_451774981) /* sqrt(2) * (c3+c7) */
236 + MULTIPLY(z3, - FIX_2_172734803) /* sqrt(2) * (-c1-c5) */
237 + MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * (c5+c7) */
238
239 tmp2 = MULTIPLY(z1, - FIX_0_509795579) /* sqrt(2) * (c7-c5) */
240 + MULTIPLY(z2, - FIX_0_601344887) /* sqrt(2) * (c5-c1) */
241 + MULTIPLY(z3, FIX_0_899976223) /* sqrt(2) * (c3-c7) */
242 + MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
243
244 /* Final output stage */
245
246 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
247 CONST_BITS+PASS1_BITS+3+1)
248 & RANGE_MASK];
249 outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
250 CONST_BITS+PASS1_BITS+3+1)
251 & RANGE_MASK];
252 outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
253 CONST_BITS+PASS1_BITS+3+1)
254 & RANGE_MASK];
255 outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
256 CONST_BITS+PASS1_BITS+3+1)
257 & RANGE_MASK];
258
259 wsptr += DCTSIZE; /* advance pointer to next row */
260 }
261 }
262
263
264 /*
265 * Perform dequantization and inverse DCT on one block of coefficients,
266 * producing a reduced-size 2x2 output block.
267 */
268
269 GLOBAL void
jpeg_idct_2x2(j_decompress_ptr cinfo,jpeg_component_info * compptr,JCOEFPTR coef_block,JSAMPARRAY output_buf,JDIMENSION output_col)270 jpeg_idct_2x2 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
271 JCOEFPTR coef_block,
272 JSAMPARRAY output_buf, JDIMENSION output_col)
273 {
274 INT32 tmp0, tmp10, z1;
275 JCOEFPTR inptr;
276 ISLOW_MULT_TYPE * quantptr;
277 int * wsptr;
278 JSAMPROW outptr;
279 JSAMPLE *range_limit = IDCT_range_limit(cinfo);
280 int ctr;
281 int workspace[DCTSIZE*2]; /* buffers data between passes */
282 SHIFT_TEMPS
283
284 /* Pass 1: process columns from input, store into work array. */
285
286 inptr = coef_block;
287 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
288 wsptr = workspace;
289 for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
290 /* Don't bother to process columns 2,4,6 */
291 if (ctr == DCTSIZE-2 || ctr == DCTSIZE-4 || ctr == DCTSIZE-6)
292 continue;
293 if ((inptr[DCTSIZE*1] | inptr[DCTSIZE*3] |
294 inptr[DCTSIZE*5] | inptr[DCTSIZE*7]) == 0) {
295 /* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
296 int dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]) << PASS1_BITS;
297
298 wsptr[DCTSIZE*0] = dcval;
299 wsptr[DCTSIZE*1] = dcval;
300
301 continue;
302 }
303
304 /* Even part */
305
306 z1 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
307 tmp10 = z1 << (CONST_BITS+2);
308
309 /* Odd part */
310
311 z1 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
312 tmp0 = MULTIPLY(z1, - FIX_0_720959822); /* sqrt(2) * (c7-c5+c3-c1) */
313 z1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
314 tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
315 z1 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
316 tmp0 += MULTIPLY(z1, - FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
317 z1 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
318 tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
319
320 /* Final output stage */
321
322 wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp0, CONST_BITS-PASS1_BITS+2);
323 wsptr[DCTSIZE*1] = (int) DESCALE(tmp10 - tmp0, CONST_BITS-PASS1_BITS+2);
324 }
325
326 /* Pass 2: process 2 rows from work array, store into output array. */
327
328 wsptr = workspace;
329 for (ctr = 0; ctr < 2; ctr++) {
330 outptr = output_buf[ctr] + output_col;
331 /* It's not clear whether a zero row test is worthwhile here ... */
332
333 #ifndef NO_ZERO_ROW_TEST
334 if ((wsptr[1] | wsptr[3] | wsptr[5] | wsptr[7]) == 0) {
335 /* AC terms all zero */
336 JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
337 & RANGE_MASK];
338
339 outptr[0] = dcval;
340 outptr[1] = dcval;
341
342 wsptr += DCTSIZE; /* advance pointer to next row */
343 continue;
344 }
345 #endif
346
347 /* Even part */
348
349 tmp10 = ((INT32) wsptr[0]) << (CONST_BITS+2);
350
351 /* Odd part */
352
353 tmp0 = MULTIPLY((INT32) wsptr[7], - FIX_0_720959822) /* sqrt(2) * (c7-c5+c3-c1) */
354 + MULTIPLY((INT32) wsptr[5], FIX_0_850430095) /* sqrt(2) * (-c1+c3+c5+c7) */
355 + MULTIPLY((INT32) wsptr[3], - FIX_1_272758580) /* sqrt(2) * (-c1+c3-c5-c7) */
356 + MULTIPLY((INT32) wsptr[1], FIX_3_624509785); /* sqrt(2) * (c1+c3+c5+c7) */
357
358 /* Final output stage */
359
360 outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp0,
361 CONST_BITS+PASS1_BITS+3+2)
362 & RANGE_MASK];
363 outptr[1] = range_limit[(int) DESCALE(tmp10 - tmp0,
364 CONST_BITS+PASS1_BITS+3+2)
365 & RANGE_MASK];
366
367 wsptr += DCTSIZE; /* advance pointer to next row */
368 }
369 }
370
371
372 /*
373 * Perform dequantization and inverse DCT on one block of coefficients,
374 * producing a reduced-size 1x1 output block.
375 */
376
377 GLOBAL void
jpeg_idct_1x1(j_decompress_ptr cinfo,jpeg_component_info * compptr,JCOEFPTR coef_block,JSAMPARRAY output_buf,JDIMENSION output_col)378 jpeg_idct_1x1 (j_decompress_ptr cinfo, jpeg_component_info * compptr,
379 JCOEFPTR coef_block,
380 JSAMPARRAY output_buf, JDIMENSION output_col)
381 {
382 int dcval;
383 ISLOW_MULT_TYPE * quantptr;
384 JSAMPLE *range_limit = IDCT_range_limit(cinfo);
385 SHIFT_TEMPS
386
387 /* We hardly need an inverse DCT routine for this: just take the
388 * average pixel value, which is one-eighth of the DC coefficient.
389 */
390 quantptr = (ISLOW_MULT_TYPE *) compptr->dct_table;
391 dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
392 dcval = (int) DESCALE((INT32) dcval, 3);
393
394 output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
395 }
396
397 #endif /* IDCT_SCALING_SUPPORTED */
398