jrevdct.c@ 9441

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1	/*
2	* jrevdct.c
3	*
4	* Copyright (C) 1991, 1992, 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 the basic inverse-DCT transformation subroutine.
9	*
10	* This implementation is based on an algorithm described in
11	* C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
12	* Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
13	* Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
14	* The primary algorithm described there uses 11 multiplies and 29 adds.
15	* We use their alternate method with 12 multiplies and 32 adds.
16	* The advantage of this method is that no data path contains more than one
17	* multiplication; this allows a very simple and accurate implementation in
18	* scaled fixed-point arithmetic, with a minimal number of shifts.
19	*
20	* I've made lots of modifications to attempt to take advantage of the
21	* sparse nature of the DCT matrices we're getting. Although the logic
22	* is cumbersome, it's straightforward and the resulting code is much
23	* faster.
24	*
25	* A better way to do this would be to pass in the DCT block as a sparse
26	* matrix, perhaps with the difference cases encoded.
27	*/
28
29	/**
30	* @file jrevdct.c
31	* Independent JPEG Group's LLM idct.
32	*/
33
34	#include "common.h"
35	#include "dsputil.h"
36
37	#define EIGHT_BIT_SAMPLES
38
39	#define DCTSIZE 8
40	#define DCTSIZE2 64
41
42	#define GLOBAL
43
44	#define RIGHT_SHIFT(x, n) ((x) >> (n))
45
46	typedef DCTELEM DCTBLOCK[DCTSIZE2];
47
48	#define CONST_BITS 13
49
50	/*
51	* This routine is specialized to the case DCTSIZE = 8.
52	*/
53
54	#if DCTSIZE != 8
55	Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
56	#endif
57
58
59	/*
60	* A 2-D IDCT can be done by 1-D IDCT on each row followed by 1-D IDCT
61	* on each column. Direct algorithms are also available, but they are
62	* much more complex and seem not to be any faster when reduced to code.
63	*
64	* The poop on this scaling stuff is as follows:
65	*
66	* Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
67	* larger than the true IDCT outputs. The final outputs are therefore
68	* a factor of N larger than desired; since N=8 this can be cured by
69	* a simple right shift at the end of the algorithm. The advantage of
70	* this arrangement is that we save two multiplications per 1-D IDCT,
71	* because the y0 and y4 inputs need not be divided by sqrt(N).
72	*
73	* We have to do addition and subtraction of the integer inputs, which
74	* is no problem, and multiplication by fractional constants, which is
75	* a problem to do in integer arithmetic. We multiply all the constants
76	* by CONST_SCALE and convert them to integer constants (thus retaining
77	* CONST_BITS bits of precision in the constants). After doing a
78	* multiplication we have to divide the product by CONST_SCALE, with proper
79	* rounding, to produce the correct output. This division can be done
80	* cheaply as a right shift of CONST_BITS bits. We postpone shifting
81	* as long as possible so that partial sums can be added together with
82	* full fractional precision.
83	*
84	* The outputs of the first pass are scaled up by PASS1_BITS bits so that
85	* they are represented to better-than-integral precision. These outputs
86	* require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
87	* with the recommended scaling. (To scale up 12-bit sample data further, an
88	* intermediate int32 array would be needed.)
89	*
90	* To avoid overflow of the 32-bit intermediate results in pass 2, we must
91	* have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26. Error analysis
92	* shows that the values given below are the most effective.
93	*/
94
95	#ifdef EIGHT_BIT_SAMPLES
96	#define PASS1_BITS 2
97	#else
98	#define PASS1_BITS 1 /* lose a little precision to avoid overflow */
99	#endif
100
101	#define ONE ((int32_t) 1)
102
103	#define CONST_SCALE (ONE << CONST_BITS)
104
105	/* Convert a positive real constant to an integer scaled by CONST_SCALE.
106	* IMPORTANT: if your compiler doesn't do this arithmetic at compile time,
107	* you will pay a significant penalty in run time. In that case, figure
108	* the correct integer constant values and insert them by hand.
109	*/
110
111	/* Actually FIX is no longer used, we precomputed them all */
112	#define FIX(x) ((int32_t) ((x) * CONST_SCALE + 0.5))
113
114	/* Descale and correctly round an int32_t value that's scaled by N bits.
115	* We assume RIGHT_SHIFT rounds towards minus infinity, so adding
116	* the fudge factor is correct for either sign of X.
117	*/
118
119	#define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)
120
121	/* Multiply an int32_t variable by an int32_t constant to yield an int32_t result.
122	* For 8-bit samples with the recommended scaling, all the variable
123	* and constant values involved are no more than 16 bits wide, so a
124	* 16x16->32 bit multiply can be used instead of a full 32x32 multiply;
125	* this provides a useful speedup on many machines.
126	* There is no way to specify a 16x16->32 multiply in portable C, but
127	* some C compilers will do the right thing if you provide the correct
128	* combination of casts.
129	* NB: for 12-bit samples, a full 32-bit multiplication will be needed.
130	*/
131
132	#ifdef EIGHT_BIT_SAMPLES
133	#ifdef SHORTxSHORT_32 /* may work if 'int' is 32 bits */
134	#define MULTIPLY(var,const) (((int16_t) (var)) * ((int16_t) (const)))
135	#endif
136	#ifdef SHORTxLCONST_32 /* known to work with Microsoft C 6.0 */
137	#define MULTIPLY(var,const) (((int16_t) (var)) * ((int32_t) (const)))
138	#endif
139	#endif
140
141	#ifndef MULTIPLY /* default definition */
142	#define MULTIPLY(var,const) ((var) * (const))
143	#endif
144
145
146	/*
147	Unlike our decoder where we approximate the FIXes, we need to use exact
148	ones here or successive P-frames will drift too much with Reference frame coding
149	*/
150	#define FIX_0_211164243 1730
151	#define FIX_0_275899380 2260
152	#define FIX_0_298631336 2446
153	#define FIX_0_390180644 3196
154	#define FIX_0_509795579 4176
155	#define FIX_0_541196100 4433
156	#define FIX_0_601344887 4926
157	#define FIX_0_765366865 6270
158	#define FIX_0_785694958 6436
159	#define FIX_0_899976223 7373
160	#define FIX_1_061594337 8697
161	#define FIX_1_111140466 9102
162	#define FIX_1_175875602 9633
163	#define FIX_1_306562965 10703
164	#define FIX_1_387039845 11363
165	#define FIX_1_451774981 11893
166	#define FIX_1_501321110 12299
167	#define FIX_1_662939225 13623
168	#define FIX_1_847759065 15137
169	#define FIX_1_961570560 16069
170	#define FIX_2_053119869 16819
171	#define FIX_2_172734803 17799
172	#define FIX_2_562915447 20995
173	#define FIX_3_072711026 25172
174
175	/*
176	* Perform the inverse DCT on one block of coefficients.
177	*/
178
179	void j_rev_dct(DCTBLOCK data)
180	{
181	int32_t tmp0, tmp1, tmp2, tmp3;
182	int32_t tmp10, tmp11, tmp12, tmp13;
183	int32_t z1, z2, z3, z4, z5;
184	int32_t d0, d1, d2, d3, d4, d5, d6, d7;
185	register DCTELEM *dataptr;
186	int rowctr;
187
188	/* Pass 1: process rows. */
189	/* Note results are scaled up by sqrt(8) compared to a true IDCT; */
190	/* furthermore, we scale the results by 2*PASS1_BITS. /
191
192	dataptr = data;
193
194	for (rowctr = DCTSIZE-1; rowctr >= 0; rowctr--) {
195	/* Due to quantization, we will usually find that many of the input
196	* coefficients are zero, especially the AC terms. We can exploit this
197	* by short-circuiting the IDCT calculation for any row in which all
198	* the AC terms are zero. In that case each output is equal to the
199	* DC coefficient (with scale factor as needed).
200	* With typical images and quantization tables, half or more of the
201	* row DCT calculations can be simplified this way.
202	*/
203
204	register int idataptr = (int)dataptr;
205
206	/* WARNING: we do the same permutation as MMX idct to simplify the
207	video core */
208	d0 = dataptr[0];
209	d2 = dataptr[1];
210	d4 = dataptr[2];
211	d6 = dataptr[3];
212	d1 = dataptr[4];
213	d3 = dataptr[5];
214	d5 = dataptr[6];
215	d7 = dataptr[7];
216
217	if ((d1 \| d2 \| d3 \| d4 \| d5 \| d6 \| d7) == 0) {
218	/* AC terms all zero */
219	if (d0) {
220	/* Compute a 32 bit value to assign. */
221	DCTELEM dcval = (DCTELEM) (d0 << PASS1_BITS);
222	register int v = (dcval & 0xffff) \| ((dcval << 16) & 0xffff0000);
223
224	idataptr[0] = v;
225	idataptr[1] = v;
226	idataptr[2] = v;
227	idataptr[3] = v;
228	}
229
230	dataptr += DCTSIZE; /* advance pointer to next row */
231	continue;
232	}
233
234	/* Even part: reverse the even part of the forward DCT. */
235	/* The rotator is sqrt(2)c(-6). /
236	{
237	if (d6) {
238	if (d2) {
239	/* d0 != 0, d2 != 0, d4 != 0, d6 != 0 */
240	z1 = MULTIPLY(d2 + d6, FIX_0_541196100);
241	tmp2 = z1 + MULTIPLY(-d6, FIX_1_847759065);
242	tmp3 = z1 + MULTIPLY(d2, FIX_0_765366865);
243
244	tmp0 = (d0 + d4) << CONST_BITS;
245	tmp1 = (d0 - d4) << CONST_BITS;
246
247	tmp10 = tmp0 + tmp3;
248	tmp13 = tmp0 - tmp3;
249	tmp11 = tmp1 + tmp2;
250	tmp12 = tmp1 - tmp2;
251	} else {
252	/* d0 != 0, d2 == 0, d4 != 0, d6 != 0 */
253	tmp2 = MULTIPLY(-d6, FIX_1_306562965);
254	tmp3 = MULTIPLY(d6, FIX_0_541196100);
255
256	tmp0 = (d0 + d4) << CONST_BITS;
257	tmp1 = (d0 - d4) << CONST_BITS;
258
259	tmp10 = tmp0 + tmp3;
260	tmp13 = tmp0 - tmp3;
261	tmp11 = tmp1 + tmp2;
262	tmp12 = tmp1 - tmp2;
263	}
264	} else {
265	if (d2) {
266	/* d0 != 0, d2 != 0, d4 != 0, d6 == 0 */
267	tmp2 = MULTIPLY(d2, FIX_0_541196100);
268	tmp3 = MULTIPLY(d2, FIX_1_306562965);
269
270	tmp0 = (d0 + d4) << CONST_BITS;
271	tmp1 = (d0 - d4) << CONST_BITS;
272
273	tmp10 = tmp0 + tmp3;
274	tmp13 = tmp0 - tmp3;
275	tmp11 = tmp1 + tmp2;
276	tmp12 = tmp1 - tmp2;
277	} else {
278	/* d0 != 0, d2 == 0, d4 != 0, d6 == 0 */
279	tmp10 = tmp13 = (d0 + d4) << CONST_BITS;
280	tmp11 = tmp12 = (d0 - d4) << CONST_BITS;
281	}
282	}
283
284	/* Odd part per figure 8; the matrix is unitary and hence its
285	* transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively.
286	*/
287
288	if (d7) {
289	if (d5) {
290	if (d3) {
291	if (d1) {
292	/* d1 != 0, d3 != 0, d5 != 0, d7 != 0 */
293	z1 = d7 + d1;
294	z2 = d5 + d3;
295	z3 = d7 + d3;
296	z4 = d5 + d1;
297	z5 = MULTIPLY(z3 + z4, FIX_1_175875602);
298
299	tmp0 = MULTIPLY(d7, FIX_0_298631336);
300	tmp1 = MULTIPLY(d5, FIX_2_053119869);
301	tmp2 = MULTIPLY(d3, FIX_3_072711026);
302	tmp3 = MULTIPLY(d1, FIX_1_501321110);
303	z1 = MULTIPLY(-z1, FIX_0_899976223);
304	z2 = MULTIPLY(-z2, FIX_2_562915447);
305	z3 = MULTIPLY(-z3, FIX_1_961570560);
306	z4 = MULTIPLY(-z4, FIX_0_390180644);
307
308	z3 += z5;
309	z4 += z5;
310
311	tmp0 += z1 + z3;
312	tmp1 += z2 + z4;
313	tmp2 += z2 + z3;
314	tmp3 += z1 + z4;
315	} else {
316	/* d1 == 0, d3 != 0, d5 != 0, d7 != 0 */
317	z2 = d5 + d3;
318	z3 = d7 + d3;
319	z5 = MULTIPLY(z3 + d5, FIX_1_175875602);
320
321	tmp0 = MULTIPLY(d7, FIX_0_298631336);
322	tmp1 = MULTIPLY(d5, FIX_2_053119869);
323	tmp2 = MULTIPLY(d3, FIX_3_072711026);
324	z1 = MULTIPLY(-d7, FIX_0_899976223);
325	z2 = MULTIPLY(-z2, FIX_2_562915447);
326	z3 = MULTIPLY(-z3, FIX_1_961570560);
327	z4 = MULTIPLY(-d5, FIX_0_390180644);
328
329	z3 += z5;
330	z4 += z5;
331
332	tmp0 += z1 + z3;
333	tmp1 += z2 + z4;
334	tmp2 += z2 + z3;
335	tmp3 = z1 + z4;
336	}
337	} else {
338	if (d1) {
339	/* d1 != 0, d3 == 0, d5 != 0, d7 != 0 */
340	z1 = d7 + d1;
341	z4 = d5 + d1;
342	z5 = MULTIPLY(d7 + z4, FIX_1_175875602);
343
344	tmp0 = MULTIPLY(d7, FIX_0_298631336);
345	tmp1 = MULTIPLY(d5, FIX_2_053119869);
346	tmp3 = MULTIPLY(d1, FIX_1_501321110);
347	z1 = MULTIPLY(-z1, FIX_0_899976223);
348	z2 = MULTIPLY(-d5, FIX_2_562915447);
349	z3 = MULTIPLY(-d7, FIX_1_961570560);
350	z4 = MULTIPLY(-z4, FIX_0_390180644);
351
352	z3 += z5;
353	z4 += z5;
354
355	tmp0 += z1 + z3;
356	tmp1 += z2 + z4;
357	tmp2 = z2 + z3;
358	tmp3 += z1 + z4;
359	} else {
360	/* d1 == 0, d3 == 0, d5 != 0, d7 != 0 */
361	tmp0 = MULTIPLY(-d7, FIX_0_601344887);
362	z1 = MULTIPLY(-d7, FIX_0_899976223);
363	z3 = MULTIPLY(-d7, FIX_1_961570560);
364	tmp1 = MULTIPLY(-d5, FIX_0_509795579);
365	z2 = MULTIPLY(-d5, FIX_2_562915447);
366	z4 = MULTIPLY(-d5, FIX_0_390180644);
367	z5 = MULTIPLY(d5 + d7, FIX_1_175875602);
368
369	z3 += z5;
370	z4 += z5;
371
372	tmp0 += z3;
373	tmp1 += z4;
374	tmp2 = z2 + z3;
375	tmp3 = z1 + z4;
376	}
377	}
378	} else {
379	if (d3) {
380	if (d1) {
381	/* d1 != 0, d3 != 0, d5 == 0, d7 != 0 */
382	z1 = d7 + d1;
383	z3 = d7 + d3;
384	z5 = MULTIPLY(z3 + d1, FIX_1_175875602);
385
386	tmp0 = MULTIPLY(d7, FIX_0_298631336);
387	tmp2 = MULTIPLY(d3, FIX_3_072711026);
388	tmp3 = MULTIPLY(d1, FIX_1_501321110);
389	z1 = MULTIPLY(-z1, FIX_0_899976223);
390	z2 = MULTIPLY(-d3, FIX_2_562915447);
391	z3 = MULTIPLY(-z3, FIX_1_961570560);
392	z4 = MULTIPLY(-d1, FIX_0_390180644);
393
394	z3 += z5;
395	z4 += z5;
396
397	tmp0 += z1 + z3;
398	tmp1 = z2 + z4;
399	tmp2 += z2 + z3;
400	tmp3 += z1 + z4;
401	} else {
402	/* d1 == 0, d3 != 0, d5 == 0, d7 != 0 */
403	z3 = d7 + d3;
404
405	tmp0 = MULTIPLY(-d7, FIX_0_601344887);
406	z1 = MULTIPLY(-d7, FIX_0_899976223);
407	tmp2 = MULTIPLY(d3, FIX_0_509795579);
408	z2 = MULTIPLY(-d3, FIX_2_562915447);
409	z5 = MULTIPLY(z3, FIX_1_175875602);
410	z3 = MULTIPLY(-z3, FIX_0_785694958);
411
412	tmp0 += z3;
413	tmp1 = z2 + z5;
414	tmp2 += z3;
415	tmp3 = z1 + z5;
416	}
417	} else {
418	if (d1) {
419	/* d1 != 0, d3 == 0, d5 == 0, d7 != 0 */
420	z1 = d7 + d1;
421	z5 = MULTIPLY(z1, FIX_1_175875602);
422
423	z1 = MULTIPLY(z1, FIX_0_275899380);
424	z3 = MULTIPLY(-d7, FIX_1_961570560);
425	tmp0 = MULTIPLY(-d7, FIX_1_662939225);
426	z4 = MULTIPLY(-d1, FIX_0_390180644);
427	tmp3 = MULTIPLY(d1, FIX_1_111140466);
428
429	tmp0 += z1;
430	tmp1 = z4 + z5;
431	tmp2 = z3 + z5;
432	tmp3 += z1;
433	} else {
434	/* d1 == 0, d3 == 0, d5 == 0, d7 != 0 */
435	tmp0 = MULTIPLY(-d7, FIX_1_387039845);
436	tmp1 = MULTIPLY(d7, FIX_1_175875602);
437	tmp2 = MULTIPLY(-d7, FIX_0_785694958);
438	tmp3 = MULTIPLY(d7, FIX_0_275899380);
439	}
440	}
441	}
442	} else {
443	if (d5) {
444	if (d3) {
445	if (d1) {
446	/* d1 != 0, d3 != 0, d5 != 0, d7 == 0 */
447	z2 = d5 + d3;
448	z4 = d5 + d1;
449	z5 = MULTIPLY(d3 + z4, FIX_1_175875602);
450
451	tmp1 = MULTIPLY(d5, FIX_2_053119869);
452	tmp2 = MULTIPLY(d3, FIX_3_072711026);
453	tmp3 = MULTIPLY(d1, FIX_1_501321110);
454	z1 = MULTIPLY(-d1, FIX_0_899976223);
455	z2 = MULTIPLY(-z2, FIX_2_562915447);
456	z3 = MULTIPLY(-d3, FIX_1_961570560);
457	z4 = MULTIPLY(-z4, FIX_0_390180644);
458
459	z3 += z5;
460	z4 += z5;
461
462	tmp0 = z1 + z3;
463	tmp1 += z2 + z4;
464	tmp2 += z2 + z3;
465	tmp3 += z1 + z4;
466	} else {
467	/* d1 == 0, d3 != 0, d5 != 0, d7 == 0 */
468	z2 = d5 + d3;
469
470	z5 = MULTIPLY(z2, FIX_1_175875602);
471	tmp1 = MULTIPLY(d5, FIX_1_662939225);
472	z4 = MULTIPLY(-d5, FIX_0_390180644);
473	z2 = MULTIPLY(-z2, FIX_1_387039845);
474	tmp2 = MULTIPLY(d3, FIX_1_111140466);
475	z3 = MULTIPLY(-d3, FIX_1_961570560);
476
477	tmp0 = z3 + z5;
478	tmp1 += z2;
479	tmp2 += z2;
480	tmp3 = z4 + z5;
481	}
482	} else {
483	if (d1) {
484	/* d1 != 0, d3 == 0, d5 != 0, d7 == 0 */
485	z4 = d5 + d1;
486
487	z5 = MULTIPLY(z4, FIX_1_175875602);
488	z1 = MULTIPLY(-d1, FIX_0_899976223);
489	tmp3 = MULTIPLY(d1, FIX_0_601344887);
490	tmp1 = MULTIPLY(-d5, FIX_0_509795579);
491	z2 = MULTIPLY(-d5, FIX_2_562915447);
492	z4 = MULTIPLY(z4, FIX_0_785694958);
493
494	tmp0 = z1 + z5;
495	tmp1 += z4;
496	tmp2 = z2 + z5;
497	tmp3 += z4;
498	} else {
499	/* d1 == 0, d3 == 0, d5 != 0, d7 == 0 */
500	tmp0 = MULTIPLY(d5, FIX_1_175875602);
501	tmp1 = MULTIPLY(d5, FIX_0_275899380);
502	tmp2 = MULTIPLY(-d5, FIX_1_387039845);
503	tmp3 = MULTIPLY(d5, FIX_0_785694958);
504	}
505	}
506	} else {
507	if (d3) {
508	if (d1) {
509	/* d1 != 0, d3 != 0, d5 == 0, d7 == 0 */
510	z5 = d1 + d3;
511	tmp3 = MULTIPLY(d1, FIX_0_211164243);
512	tmp2 = MULTIPLY(-d3, FIX_1_451774981);
513	z1 = MULTIPLY(d1, FIX_1_061594337);
514	z2 = MULTIPLY(-d3, FIX_2_172734803);
515	z4 = MULTIPLY(z5, FIX_0_785694958);
516	z5 = MULTIPLY(z5, FIX_1_175875602);
517
518	tmp0 = z1 - z4;
519	tmp1 = z2 + z4;
520	tmp2 += z5;
521	tmp3 += z5;
522	} else {
523	/* d1 == 0, d3 != 0, d5 == 0, d7 == 0 */
524	tmp0 = MULTIPLY(-d3, FIX_0_785694958);
525	tmp1 = MULTIPLY(-d3, FIX_1_387039845);
526	tmp2 = MULTIPLY(-d3, FIX_0_275899380);
527	tmp3 = MULTIPLY(d3, FIX_1_175875602);
528	}
529	} else {
530	if (d1) {
531	/* d1 != 0, d3 == 0, d5 == 0, d7 == 0 */
532	tmp0 = MULTIPLY(d1, FIX_0_275899380);
533	tmp1 = MULTIPLY(d1, FIX_0_785694958);
534	tmp2 = MULTIPLY(d1, FIX_1_175875602);
535	tmp3 = MULTIPLY(d1, FIX_1_387039845);
536	} else {
537	/* d1 == 0, d3 == 0, d5 == 0, d7 == 0 */
538	tmp0 = tmp1 = tmp2 = tmp3 = 0;
539	}
540	}
541	}
542	}
543	}
544	/* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
545
546	dataptr[0] = (DCTELEM) DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS);
547	dataptr[7] = (DCTELEM) DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS);
548	dataptr[1] = (DCTELEM) DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS);
549	dataptr[6] = (DCTELEM) DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS);
550	dataptr[2] = (DCTELEM) DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS);
551	dataptr[5] = (DCTELEM) DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS);
552	dataptr[3] = (DCTELEM) DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS);
553	dataptr[4] = (DCTELEM) DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS);
554
555	dataptr += DCTSIZE; /* advance pointer to next row */
556	}
557
558	/* Pass 2: process columns. */
559	/* Note that we must descale the results by a factor of 8 == 2*3, /
560	/* and also undo the PASS1_BITS scaling. */
561
562	dataptr = data;
563	for (rowctr = DCTSIZE-1; rowctr >= 0; rowctr--) {
564	/* Columns of zeroes can be exploited in the same way as we did with rows.
565	* However, the row calculation has created many nonzero AC terms, so the
566	* simplification applies less often (typically 5% to 10% of the time).
567	* On machines with very fast multiplication, it's possible that the
568	* test takes more time than it's worth. In that case this section
569	* may be commented out.
570	*/
571
572	d0 = dataptr[DCTSIZE*0];
573	d1 = dataptr[DCTSIZE*1];
574	d2 = dataptr[DCTSIZE*2];
575	d3 = dataptr[DCTSIZE*3];
576	d4 = dataptr[DCTSIZE*4];
577	d5 = dataptr[DCTSIZE*5];
578	d6 = dataptr[DCTSIZE*6];
579	d7 = dataptr[DCTSIZE*7];
580
581	/* Even part: reverse the even part of the forward DCT. */
582	/* The rotator is sqrt(2)c(-6). /
583	if (d6) {
584	if (d2) {
585	/* d0 != 0, d2 != 0, d4 != 0, d6 != 0 */
586	z1 = MULTIPLY(d2 + d6, FIX_0_541196100);
587	tmp2 = z1 + MULTIPLY(-d6, FIX_1_847759065);
588	tmp3 = z1 + MULTIPLY(d2, FIX_0_765366865);
589
590	tmp0 = (d0 + d4) << CONST_BITS;
591	tmp1 = (d0 - d4) << CONST_BITS;
592
593	tmp10 = tmp0 + tmp3;
594	tmp13 = tmp0 - tmp3;
595	tmp11 = tmp1 + tmp2;
596	tmp12 = tmp1 - tmp2;
597	} else {
598	/* d0 != 0, d2 == 0, d4 != 0, d6 != 0 */
599	tmp2 = MULTIPLY(-d6, FIX_1_306562965);
600	tmp3 = MULTIPLY(d6, FIX_0_541196100);
601
602	tmp0 = (d0 + d4) << CONST_BITS;
603	tmp1 = (d0 - d4) << CONST_BITS;
604
605	tmp10 = tmp0 + tmp3;
606	tmp13 = tmp0 - tmp3;
607	tmp11 = tmp1 + tmp2;
608	tmp12 = tmp1 - tmp2;
609	}
610	} else {
611	if (d2) {
612	/* d0 != 0, d2 != 0, d4 != 0, d6 == 0 */
613	tmp2 = MULTIPLY(d2, FIX_0_541196100);
614	tmp3 = MULTIPLY(d2, FIX_1_306562965);
615
616	tmp0 = (d0 + d4) << CONST_BITS;
617	tmp1 = (d0 - d4) << CONST_BITS;
618
619	tmp10 = tmp0 + tmp3;
620	tmp13 = tmp0 - tmp3;
621	tmp11 = tmp1 + tmp2;
622	tmp12 = tmp1 - tmp2;
623	} else {
624	/* d0 != 0, d2 == 0, d4 != 0, d6 == 0 */
625	tmp10 = tmp13 = (d0 + d4) << CONST_BITS;
626	tmp11 = tmp12 = (d0 - d4) << CONST_BITS;
627	}
628	}
629
630	/* Odd part per figure 8; the matrix is unitary and hence its
631	* transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively.
632	*/
633	if (d7) {
634	if (d5) {
635	if (d3) {
636	if (d1) {
637	/* d1 != 0, d3 != 0, d5 != 0, d7 != 0 */
638	z1 = d7 + d1;
639	z2 = d5 + d3;
640	z3 = d7 + d3;
641	z4 = d5 + d1;
642	z5 = MULTIPLY(z3 + z4, FIX_1_175875602);
643
644	tmp0 = MULTIPLY(d7, FIX_0_298631336);
645	tmp1 = MULTIPLY(d5, FIX_2_053119869);
646	tmp2 = MULTIPLY(d3, FIX_3_072711026);
647	tmp3 = MULTIPLY(d1, FIX_1_501321110);
648	z1 = MULTIPLY(-z1, FIX_0_899976223);
649	z2 = MULTIPLY(-z2, FIX_2_562915447);
650	z3 = MULTIPLY(-z3, FIX_1_961570560);
651	z4 = MULTIPLY(-z4, FIX_0_390180644);
652
653	z3 += z5;
654	z4 += z5;
655
656	tmp0 += z1 + z3;
657	tmp1 += z2 + z4;
658	tmp2 += z2 + z3;
659	tmp3 += z1 + z4;
660	} else {
661	/* d1 == 0, d3 != 0, d5 != 0, d7 != 0 */
662	z1 = d7;
663	z2 = d5 + d3;
664	z3 = d7 + d3;
665	z5 = MULTIPLY(z3 + d5, FIX_1_175875602);
666
667	tmp0 = MULTIPLY(d7, FIX_0_298631336);
668	tmp1 = MULTIPLY(d5, FIX_2_053119869);
669	tmp2 = MULTIPLY(d3, FIX_3_072711026);
670	z1 = MULTIPLY(-d7, FIX_0_899976223);
671	z2 = MULTIPLY(-z2, FIX_2_562915447);
672	z3 = MULTIPLY(-z3, FIX_1_961570560);
673	z4 = MULTIPLY(-d5, FIX_0_390180644);
674
675	z3 += z5;
676	z4 += z5;
677
678	tmp0 += z1 + z3;
679	tmp1 += z2 + z4;
680	tmp2 += z2 + z3;
681	tmp3 = z1 + z4;
682	}
683	} else {
684	if (d1) {
685	/* d1 != 0, d3 == 0, d5 != 0, d7 != 0 */
686	z1 = d7 + d1;
687	z2 = d5;
688	z3 = d7;
689	z4 = d5 + d1;
690	z5 = MULTIPLY(z3 + z4, FIX_1_175875602);
691
692	tmp0 = MULTIPLY(d7, FIX_0_298631336);
693	tmp1 = MULTIPLY(d5, FIX_2_053119869);
694	tmp3 = MULTIPLY(d1, FIX_1_501321110);
695	z1 = MULTIPLY(-z1, FIX_0_899976223);
696	z2 = MULTIPLY(-d5, FIX_2_562915447);
697	z3 = MULTIPLY(-d7, FIX_1_961570560);
698	z4 = MULTIPLY(-z4, FIX_0_390180644);
699
700	z3 += z5;
701	z4 += z5;
702
703	tmp0 += z1 + z3;
704	tmp1 += z2 + z4;
705	tmp2 = z2 + z3;
706	tmp3 += z1 + z4;
707	} else {
708	/* d1 == 0, d3 == 0, d5 != 0, d7 != 0 */
709	tmp0 = MULTIPLY(-d7, FIX_0_601344887);
710	z1 = MULTIPLY(-d7, FIX_0_899976223);
711	z3 = MULTIPLY(-d7, FIX_1_961570560);
712	tmp1 = MULTIPLY(-d5, FIX_0_509795579);
713	z2 = MULTIPLY(-d5, FIX_2_562915447);
714	z4 = MULTIPLY(-d5, FIX_0_390180644);
715	z5 = MULTIPLY(d5 + d7, FIX_1_175875602);
716
717	z3 += z5;
718	z4 += z5;
719
720	tmp0 += z3;
721	tmp1 += z4;
722	tmp2 = z2 + z3;
723	tmp3 = z1 + z4;
724	}
725	}
726	} else {
727	if (d3) {
728	if (d1) {
729	/* d1 != 0, d3 != 0, d5 == 0, d7 != 0 */
730	z1 = d7 + d1;
731	z3 = d7 + d3;
732	z5 = MULTIPLY(z3 + d1, FIX_1_175875602);
733
734	tmp0 = MULTIPLY(d7, FIX_0_298631336);
735	tmp2 = MULTIPLY(d3, FIX_3_072711026);
736	tmp3 = MULTIPLY(d1, FIX_1_501321110);
737	z1 = MULTIPLY(-z1, FIX_0_899976223);
738	z2 = MULTIPLY(-d3, FIX_2_562915447);
739	z3 = MULTIPLY(-z3, FIX_1_961570560);
740	z4 = MULTIPLY(-d1, FIX_0_390180644);
741
742	z3 += z5;
743	z4 += z5;
744
745	tmp0 += z1 + z3;
746	tmp1 = z2 + z4;
747	tmp2 += z2 + z3;
748	tmp3 += z1 + z4;
749	} else {
750	/* d1 == 0, d3 != 0, d5 == 0, d7 != 0 */
751	z3 = d7 + d3;
752
753	tmp0 = MULTIPLY(-d7, FIX_0_601344887);
754	z1 = MULTIPLY(-d7, FIX_0_899976223);
755	tmp2 = MULTIPLY(d3, FIX_0_509795579);
756	z2 = MULTIPLY(-d3, FIX_2_562915447);
757	z5 = MULTIPLY(z3, FIX_1_175875602);
758	z3 = MULTIPLY(-z3, FIX_0_785694958);
759
760	tmp0 += z3;
761	tmp1 = z2 + z5;
762	tmp2 += z3;
763	tmp3 = z1 + z5;
764	}
765	} else {
766	if (d1) {
767	/* d1 != 0, d3 == 0, d5 == 0, d7 != 0 */
768	z1 = d7 + d1;
769	z5 = MULTIPLY(z1, FIX_1_175875602);
770
771	z1 = MULTIPLY(z1, FIX_0_275899380);
772	z3 = MULTIPLY(-d7, FIX_1_961570560);
773	tmp0 = MULTIPLY(-d7, FIX_1_662939225);
774	z4 = MULTIPLY(-d1, FIX_0_390180644);
775	tmp3 = MULTIPLY(d1, FIX_1_111140466);
776
777	tmp0 += z1;
778	tmp1 = z4 + z5;
779	tmp2 = z3 + z5;
780	tmp3 += z1;
781	} else {
782	/* d1 == 0, d3 == 0, d5 == 0, d7 != 0 */
783	tmp0 = MULTIPLY(-d7, FIX_1_387039845);
784	tmp1 = MULTIPLY(d7, FIX_1_175875602);
785	tmp2 = MULTIPLY(-d7, FIX_0_785694958);
786	tmp3 = MULTIPLY(d7, FIX_0_275899380);
787	}
788	}
789	}
790	} else {
791	if (d5) {
792	if (d3) {
793	if (d1) {
794	/* d1 != 0, d3 != 0, d5 != 0, d7 == 0 */
795	z2 = d5 + d3;
796	z4 = d5 + d1;
797	z5 = MULTIPLY(d3 + z4, FIX_1_175875602);
798
799	tmp1 = MULTIPLY(d5, FIX_2_053119869);
800	tmp2 = MULTIPLY(d3, FIX_3_072711026);
801	tmp3 = MULTIPLY(d1, FIX_1_501321110);
802	z1 = MULTIPLY(-d1, FIX_0_899976223);
803	z2 = MULTIPLY(-z2, FIX_2_562915447);
804	z3 = MULTIPLY(-d3, FIX_1_961570560);
805	z4 = MULTIPLY(-z4, FIX_0_390180644);
806
807	z3 += z5;
808	z4 += z5;
809
810	tmp0 = z1 + z3;
811	tmp1 += z2 + z4;
812	tmp2 += z2 + z3;
813	tmp3 += z1 + z4;
814	} else {
815	/* d1 == 0, d3 != 0, d5 != 0, d7 == 0 */
816	z2 = d5 + d3;
817
818	z5 = MULTIPLY(z2, FIX_1_175875602);
819	tmp1 = MULTIPLY(d5, FIX_1_662939225);
820	z4 = MULTIPLY(-d5, FIX_0_390180644);
821	z2 = MULTIPLY(-z2, FIX_1_387039845);
822	tmp2 = MULTIPLY(d3, FIX_1_111140466);
823	z3 = MULTIPLY(-d3, FIX_1_961570560);
824
825	tmp0 = z3 + z5;
826	tmp1 += z2;
827	tmp2 += z2;
828	tmp3 = z4 + z5;
829	}
830	} else {
831	if (d1) {
832	/* d1 != 0, d3 == 0, d5 != 0, d7 == 0 */
833	z4 = d5 + d1;
834
835	z5 = MULTIPLY(z4, FIX_1_175875602);
836	z1 = MULTIPLY(-d1, FIX_0_899976223);
837	tmp3 = MULTIPLY(d1, FIX_0_601344887);
838	tmp1 = MULTIPLY(-d5, FIX_0_509795579);
839	z2 = MULTIPLY(-d5, FIX_2_562915447);
840	z4 = MULTIPLY(z4, FIX_0_785694958);
841
842	tmp0 = z1 + z5;
843	tmp1 += z4;
844	tmp2 = z2 + z5;
845	tmp3 += z4;
846	} else {
847	/* d1 == 0, d3 == 0, d5 != 0, d7 == 0 */
848	tmp0 = MULTIPLY(d5, FIX_1_175875602);
849	tmp1 = MULTIPLY(d5, FIX_0_275899380);
850	tmp2 = MULTIPLY(-d5, FIX_1_387039845);
851	tmp3 = MULTIPLY(d5, FIX_0_785694958);
852	}
853	}
854	} else {
855	if (d3) {
856	if (d1) {
857	/* d1 != 0, d3 != 0, d5 == 0, d7 == 0 */
858	z5 = d1 + d3;
859	tmp3 = MULTIPLY(d1, FIX_0_211164243);
860	tmp2 = MULTIPLY(-d3, FIX_1_451774981);
861	z1 = MULTIPLY(d1, FIX_1_061594337);
862	z2 = MULTIPLY(-d3, FIX_2_172734803);
863	z4 = MULTIPLY(z5, FIX_0_785694958);
864	z5 = MULTIPLY(z5, FIX_1_175875602);
865
866	tmp0 = z1 - z4;
867	tmp1 = z2 + z4;
868	tmp2 += z5;
869	tmp3 += z5;
870	} else {
871	/* d1 == 0, d3 != 0, d5 == 0, d7 == 0 */
872	tmp0 = MULTIPLY(-d3, FIX_0_785694958);
873	tmp1 = MULTIPLY(-d3, FIX_1_387039845);
874	tmp2 = MULTIPLY(-d3, FIX_0_275899380);
875	tmp3 = MULTIPLY(d3, FIX_1_175875602);
876	}
877	} else {
878	if (d1) {
879	/* d1 != 0, d3 == 0, d5 == 0, d7 == 0 */
880	tmp0 = MULTIPLY(d1, FIX_0_275899380);
881	tmp1 = MULTIPLY(d1, FIX_0_785694958);
882	tmp2 = MULTIPLY(d1, FIX_1_175875602);
883	tmp3 = MULTIPLY(d1, FIX_1_387039845);
884	} else {
885	/* d1 == 0, d3 == 0, d5 == 0, d7 == 0 */
886	tmp0 = tmp1 = tmp2 = tmp3 = 0;
887	}
888	}
889	}
890	}
891
892	/* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
893
894	dataptr[DCTSIZE*0] = (DCTELEM) DESCALE(tmp10 + tmp3,
895	CONST_BITS+PASS1_BITS+3);
896	dataptr[DCTSIZE*7] = (DCTELEM) DESCALE(tmp10 - tmp3,
897	CONST_BITS+PASS1_BITS+3);
898	dataptr[DCTSIZE*1] = (DCTELEM) DESCALE(tmp11 + tmp2,
899	CONST_BITS+PASS1_BITS+3);
900	dataptr[DCTSIZE*6] = (DCTELEM) DESCALE(tmp11 - tmp2,
901	CONST_BITS+PASS1_BITS+3);
902	dataptr[DCTSIZE*2] = (DCTELEM) DESCALE(tmp12 + tmp1,
903	CONST_BITS+PASS1_BITS+3);
904	dataptr[DCTSIZE*5] = (DCTELEM) DESCALE(tmp12 - tmp1,
905	CONST_BITS+PASS1_BITS+3);
906	dataptr[DCTSIZE*3] = (DCTELEM) DESCALE(tmp13 + tmp0,
907	CONST_BITS+PASS1_BITS+3);
908	dataptr[DCTSIZE*4] = (DCTELEM) DESCALE(tmp13 - tmp0,
909	CONST_BITS+PASS1_BITS+3);
910
911	dataptr++; /* advance pointer to next column */
912	}
913	}
914
915	#undef DCTSIZE
916	#define DCTSIZE 4
917	#define DCTSTRIDE 8
918
919	void j_rev_dct4(DCTBLOCK data)
920	{
921	int32_t tmp0, tmp1, tmp2, tmp3;
922	int32_t tmp10, tmp11, tmp12, tmp13;
923	int32_t z1;
924	int32_t d0, d2, d4, d6;
925	register DCTELEM *dataptr;
926	int rowctr;
927
928	/* Pass 1: process rows. */
929	/* Note results are scaled up by sqrt(8) compared to a true IDCT; */
930	/* furthermore, we scale the results by 2*PASS1_BITS. /
931
932	data[0] += 4;
933
934	dataptr = data;
935
936	for (rowctr = DCTSIZE-1; rowctr >= 0; rowctr--) {
937	/* Due to quantization, we will usually find that many of the input
938	* coefficients are zero, especially the AC terms. We can exploit this
939	* by short-circuiting the IDCT calculation for any row in which all
940	* the AC terms are zero. In that case each output is equal to the
941	* DC coefficient (with scale factor as needed).
942	* With typical images and quantization tables, half or more of the
943	* row DCT calculations can be simplified this way.
944	*/
945
946	register int idataptr = (int)dataptr;
947
948	d0 = dataptr[0];
949	d2 = dataptr[1];
950	d4 = dataptr[2];
951	d6 = dataptr[3];
952
953	if ((d2 \| d4 \| d6) == 0) {
954	/* AC terms all zero */
955	if (d0) {
956	/* Compute a 32 bit value to assign. */
957	DCTELEM dcval = (DCTELEM) (d0 << PASS1_BITS);
958	register int v = (dcval & 0xffff) \| ((dcval << 16) & 0xffff0000);
959
960	idataptr[0] = v;
961	idataptr[1] = v;
962	}
963
964	dataptr += DCTSTRIDE; /* advance pointer to next row */
965	continue;
966	}
967
968	/* Even part: reverse the even part of the forward DCT. */
969	/* The rotator is sqrt(2)c(-6). /
970	if (d6) {
971	if (d2) {
972	/* d0 != 0, d2 != 0, d4 != 0, d6 != 0 */
973	z1 = MULTIPLY(d2 + d6, FIX_0_541196100);
974	tmp2 = z1 + MULTIPLY(-d6, FIX_1_847759065);
975	tmp3 = z1 + MULTIPLY(d2, FIX_0_765366865);
976
977	tmp0 = (d0 + d4) << CONST_BITS;
978	tmp1 = (d0 - d4) << CONST_BITS;
979
980	tmp10 = tmp0 + tmp3;
981	tmp13 = tmp0 - tmp3;
982	tmp11 = tmp1 + tmp2;
983	tmp12 = tmp1 - tmp2;
984	} else {
985	/* d0 != 0, d2 == 0, d4 != 0, d6 != 0 */
986	tmp2 = MULTIPLY(-d6, FIX_1_306562965);
987	tmp3 = MULTIPLY(d6, FIX_0_541196100);
988
989	tmp0 = (d0 + d4) << CONST_BITS;
990	tmp1 = (d0 - d4) << CONST_BITS;
991
992	tmp10 = tmp0 + tmp3;
993	tmp13 = tmp0 - tmp3;
994	tmp11 = tmp1 + tmp2;
995	tmp12 = tmp1 - tmp2;
996	}
997	} else {
998	if (d2) {
999	/* d0 != 0, d2 != 0, d4 != 0, d6 == 0 */
1000	tmp2 = MULTIPLY(d2, FIX_0_541196100);
1001	tmp3 = MULTIPLY(d2, FIX_1_306562965);
1002
1003	tmp0 = (d0 + d4) << CONST_BITS;
1004	tmp1 = (d0 - d4) << CONST_BITS;
1005
1006	tmp10 = tmp0 + tmp3;
1007	tmp13 = tmp0 - tmp3;
1008	tmp11 = tmp1 + tmp2;
1009	tmp12 = tmp1 - tmp2;
1010	} else {
1011	/* d0 != 0, d2 == 0, d4 != 0, d6 == 0 */
1012	tmp10 = tmp13 = (d0 + d4) << CONST_BITS;
1013	tmp11 = tmp12 = (d0 - d4) << CONST_BITS;
1014	}
1015	}
1016
1017	/* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
1018
1019	dataptr[0] = (DCTELEM) DESCALE(tmp10, CONST_BITS-PASS1_BITS);
1020	dataptr[1] = (DCTELEM) DESCALE(tmp11, CONST_BITS-PASS1_BITS);
1021	dataptr[2] = (DCTELEM) DESCALE(tmp12, CONST_BITS-PASS1_BITS);
1022	dataptr[3] = (DCTELEM) DESCALE(tmp13, CONST_BITS-PASS1_BITS);
1023
1024	dataptr += DCTSTRIDE; /* advance pointer to next row */
1025	}
1026
1027	/* Pass 2: process columns. */
1028	/* Note that we must descale the results by a factor of 8 == 2*3, /
1029	/* and also undo the PASS1_BITS scaling. */
1030
1031	dataptr = data;
1032	for (rowctr = DCTSIZE-1; rowctr >= 0; rowctr--) {
1033	/* Columns of zeroes can be exploited in the same way as we did with rows.
1034	* However, the row calculation has created many nonzero AC terms, so the
1035	* simplification applies less often (typically 5% to 10% of the time).
1036	* On machines with very fast multiplication, it's possible that the
1037	* test takes more time than it's worth. In that case this section
1038	* may be commented out.
1039	*/
1040
1041	d0 = dataptr[DCTSTRIDE*0];
1042	d2 = dataptr[DCTSTRIDE*1];
1043	d4 = dataptr[DCTSTRIDE*2];
1044	d6 = dataptr[DCTSTRIDE*3];
1045
1046	/* Even part: reverse the even part of the forward DCT. */
1047	/* The rotator is sqrt(2)c(-6). /
1048	if (d6) {
1049	if (d2) {
1050	/* d0 != 0, d2 != 0, d4 != 0, d6 != 0 */
1051	z1 = MULTIPLY(d2 + d6, FIX_0_541196100);
1052	tmp2 = z1 + MULTIPLY(-d6, FIX_1_847759065);
1053	tmp3 = z1 + MULTIPLY(d2, FIX_0_765366865);
1054
1055	tmp0 = (d0 + d4) << CONST_BITS;
1056	tmp1 = (d0 - d4) << CONST_BITS;
1057
1058	tmp10 = tmp0 + tmp3;
1059	tmp13 = tmp0 - tmp3;
1060	tmp11 = tmp1 + tmp2;
1061	tmp12 = tmp1 - tmp2;
1062	} else {
1063	/* d0 != 0, d2 == 0, d4 != 0, d6 != 0 */
1064	tmp2 = MULTIPLY(-d6, FIX_1_306562965);
1065	tmp3 = MULTIPLY(d6, FIX_0_541196100);
1066
1067	tmp0 = (d0 + d4) << CONST_BITS;
1068	tmp1 = (d0 - d4) << CONST_BITS;
1069
1070	tmp10 = tmp0 + tmp3;
1071	tmp13 = tmp0 - tmp3;
1072	tmp11 = tmp1 + tmp2;
1073	tmp12 = tmp1 - tmp2;
1074	}
1075	} else {
1076	if (d2) {
1077	/* d0 != 0, d2 != 0, d4 != 0, d6 == 0 */
1078	tmp2 = MULTIPLY(d2, FIX_0_541196100);
1079	tmp3 = MULTIPLY(d2, FIX_1_306562965);
1080
1081	tmp0 = (d0 + d4) << CONST_BITS;
1082	tmp1 = (d0 - d4) << CONST_BITS;
1083
1084	tmp10 = tmp0 + tmp3;
1085	tmp13 = tmp0 - tmp3;
1086	tmp11 = tmp1 + tmp2;
1087	tmp12 = tmp1 - tmp2;
1088	} else {
1089	/* d0 != 0, d2 == 0, d4 != 0, d6 == 0 */
1090	tmp10 = tmp13 = (d0 + d4) << CONST_BITS;
1091	tmp11 = tmp12 = (d0 - d4) << CONST_BITS;
1092	}
1093	}
1094
1095	/* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
1096
1097	dataptr[DCTSTRIDE*0] = tmp10 >> (CONST_BITS+PASS1_BITS+3);
1098	dataptr[DCTSTRIDE*1] = tmp11 >> (CONST_BITS+PASS1_BITS+3);
1099	dataptr[DCTSTRIDE*2] = tmp12 >> (CONST_BITS+PASS1_BITS+3);
1100	dataptr[DCTSTRIDE*3] = tmp13 >> (CONST_BITS+PASS1_BITS+3);
1101
1102	dataptr++; /* advance pointer to next column */
1103	}
1104	}
1105
1106	void j_rev_dct2(DCTBLOCK data){
1107	int d00, d01, d10, d11;
1108
1109	data[0] += 4;
1110	d00 = data[0+0DCTSTRIDE] + data[1+0DCTSTRIDE];
1111	d01 = data[0+0DCTSTRIDE] - data[1+0DCTSTRIDE];
1112	d10 = data[0+1DCTSTRIDE] + data[1+1DCTSTRIDE];
1113	d11 = data[0+1DCTSTRIDE] - data[1+1DCTSTRIDE];
1114
1115	data[0+0*DCTSTRIDE]= (d00 + d10)>>3;
1116	data[1+0*DCTSTRIDE]= (d01 + d11)>>3;
1117	data[0+1*DCTSTRIDE]= (d00 - d10)>>3;
1118	data[1+1*DCTSTRIDE]= (d01 - d11)>>3;
1119	}
1120
1121	void j_rev_dct1(DCTBLOCK data){
1122	data[0] = (data[0] + 4)>>3;
1123	}
1124
1125	#undef FIX
1126	#undef CONST_BITS

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source: vbox/trunk/src/libs/ffmpeg-20060710/libavcodec/jrevdct.c@ 9441

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