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jidctred.c
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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 */
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
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 */
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
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);
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 */
#define DESCALE(x, n)
Definition: jdct.h:146
#define IDCT_range_limit(cinfo)
Definition: jdct.h:76
char JSAMPLE
Definition: jmorecfg.h:64
JSAMPLE FAR * JSAMPROW
Definition: jpeglib.h:79
case const int
Definition: Callbacks.cpp:52
#define RANGE_MASK
Definition: jdct.h:78
long INT32
Definition: jmorecfg.h:154
#define SHIFT_TEMPS
Definition: jpegint.h:287
MULTIPLIER ISLOW_MULT_TYPE
Definition: jdct.h:56
JCOEF FAR * JCOEFPTR
Definition: jpeglib.h:88
#define GLOBAL
Definition: jmorecfg.h:190
JSAMPROW * JSAMPARRAY
Definition: jpeglib.h:80
#define DCTSIZE
Definition: jpeglib.h:42
unsigned int JDIMENSION
Definition: jmorecfg.h:177
#define DEQUANTIZE(coef, quantval)
Definition: jidctflt.c:60