Statistics
| Branch: | Revision:

ffmpeg / libavcodec / jfdctint.c @ 11e29a41

History | View | Annotate | Download (13.7 KB)

1 28db7fce Michael Niedermayer
/*
2
 * jfdctint.c
3
 *
4
 * Copyright (C) 1991-1996, 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 a slow-but-accurate integer implementation of the
9
 * forward DCT (Discrete Cosine Transform).
10
 *
11
 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
12
 * on each column.  Direct algorithms are also available, but they are
13
 * much more complex and seem not to be any faster when reduced to code.
14
 *
15
 * This implementation is based on an algorithm described in
16
 *   C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
17
 *   Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
18
 *   Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
19
 * The primary algorithm described there uses 11 multiplies and 29 adds.
20
 * We use their alternate method with 12 multiplies and 32 adds.
21
 * The advantage of this method is that no data path contains more than one
22
 * multiplication; this allows a very simple and accurate implementation in
23
 * scaled fixed-point arithmetic, with a minimal number of shifts.
24
 */
25
26 983e3246 Michael Niedermayer
/**
27
 * @file jfdctint.c
28
 * Independent JPEG Group's slow & accurate dct.
29
 */
30
 
31 28db7fce Michael Niedermayer
#include <stdlib.h>
32
#include <stdio.h>
33
#include "common.h"
34
#include "dsputil.h"
35
36
#define SHIFT_TEMPS
37
#define DCTSIZE 8
38 004c18ee Michael Niedermayer
#define BITS_IN_JSAMPLE 8
39 28db7fce Michael Niedermayer
#define GLOBAL(x) x
40
#define RIGHT_SHIFT(x, n) ((x) >> (n))
41 004c18ee Michael Niedermayer
#define MULTIPLY16C16(var,const) ((var)*(const))
42 28db7fce Michael Niedermayer
43
#if 1 //def USE_ACCURATE_ROUNDING
44
#define DESCALE(x,n)  RIGHT_SHIFT((x) + (1 << ((n) - 1)), n)
45
#else
46
#define DESCALE(x,n)  RIGHT_SHIFT(x, n)
47
#endif
48
49
50
/*
51
 * This module 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
 * The poop on this scaling stuff is as follows:
61
 *
62
 * Each 1-D DCT step produces outputs which are a factor of sqrt(N)
63
 * larger than the true DCT outputs.  The final outputs are therefore
64
 * a factor of N larger than desired; since N=8 this can be cured by
65
 * a simple right shift at the end of the algorithm.  The advantage of
66
 * this arrangement is that we save two multiplications per 1-D DCT,
67
 * because the y0 and y4 outputs need not be divided by sqrt(N).
68
 * In the IJG code, this factor of 8 is removed by the quantization step
69
 * (in jcdctmgr.c), NOT in this module.
70
 *
71
 * We have to do addition and subtraction of the integer inputs, which
72
 * is no problem, and multiplication by fractional constants, which is
73
 * a problem to do in integer arithmetic.  We multiply all the constants
74
 * by CONST_SCALE and convert them to integer constants (thus retaining
75
 * CONST_BITS bits of precision in the constants).  After doing a
76
 * multiplication we have to divide the product by CONST_SCALE, with proper
77
 * rounding, to produce the correct output.  This division can be done
78
 * cheaply as a right shift of CONST_BITS bits.  We postpone shifting
79
 * as long as possible so that partial sums can be added together with
80
 * full fractional precision.
81
 *
82
 * The outputs of the first pass are scaled up by PASS1_BITS bits so that
83
 * they are represented to better-than-integral precision.  These outputs
84
 * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
85
 * with the recommended scaling.  (For 12-bit sample data, the intermediate
86 0c1a9eda Zdenek Kabelac
 * array is int32_t anyway.)
87 28db7fce Michael Niedermayer
 *
88
 * To avoid overflow of the 32-bit intermediate results in pass 2, we must
89
 * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26.  Error analysis
90
 * shows that the values given below are the most effective.
91
 */
92
93
#if BITS_IN_JSAMPLE == 8
94
#define CONST_BITS  13
95 004c18ee Michael Niedermayer
#define PASS1_BITS  4                /* set this to 2 if 16x16 multiplies are faster */
96 28db7fce Michael Niedermayer
#else
97
#define CONST_BITS  13
98
#define PASS1_BITS  1                /* lose a little precision to avoid overflow */
99
#endif
100
101
/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
102
 * causing a lot of useless floating-point operations at run time.
103
 * To get around this we use the following pre-calculated constants.
104
 * If you change CONST_BITS you may want to add appropriate values.
105
 * (With a reasonable C compiler, you can just rely on the FIX() macro...)
106
 */
107
108
#if CONST_BITS == 13
109 0c1a9eda Zdenek Kabelac
#define FIX_0_298631336  ((int32_t)  2446)        /* FIX(0.298631336) */
110
#define FIX_0_390180644  ((int32_t)  3196)        /* FIX(0.390180644) */
111
#define FIX_0_541196100  ((int32_t)  4433)        /* FIX(0.541196100) */
112
#define FIX_0_765366865  ((int32_t)  6270)        /* FIX(0.765366865) */
113
#define FIX_0_899976223  ((int32_t)  7373)        /* FIX(0.899976223) */
114
#define FIX_1_175875602  ((int32_t)  9633)        /* FIX(1.175875602) */
115
#define FIX_1_501321110  ((int32_t)  12299)        /* FIX(1.501321110) */
116
#define FIX_1_847759065  ((int32_t)  15137)        /* FIX(1.847759065) */
117
#define FIX_1_961570560  ((int32_t)  16069)        /* FIX(1.961570560) */
118
#define FIX_2_053119869  ((int32_t)  16819)        /* FIX(2.053119869) */
119
#define FIX_2_562915447  ((int32_t)  20995)        /* FIX(2.562915447) */
120
#define FIX_3_072711026  ((int32_t)  25172)        /* FIX(3.072711026) */
121 28db7fce Michael Niedermayer
#else
122
#define FIX_0_298631336  FIX(0.298631336)
123
#define FIX_0_390180644  FIX(0.390180644)
124
#define FIX_0_541196100  FIX(0.541196100)
125
#define FIX_0_765366865  FIX(0.765366865)
126
#define FIX_0_899976223  FIX(0.899976223)
127
#define FIX_1_175875602  FIX(1.175875602)
128
#define FIX_1_501321110  FIX(1.501321110)
129
#define FIX_1_847759065  FIX(1.847759065)
130
#define FIX_1_961570560  FIX(1.961570560)
131
#define FIX_2_053119869  FIX(2.053119869)
132
#define FIX_2_562915447  FIX(2.562915447)
133
#define FIX_3_072711026  FIX(3.072711026)
134
#endif
135
136
137 0c1a9eda Zdenek Kabelac
/* Multiply an int32_t variable by an int32_t constant to yield an int32_t result.
138 28db7fce Michael Niedermayer
 * For 8-bit samples with the recommended scaling, all the variable
139
 * and constant values involved are no more than 16 bits wide, so a
140
 * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
141
 * For 12-bit samples, a full 32-bit multiplication will be needed.
142
 */
143
144 004c18ee Michael Niedermayer
#if BITS_IN_JSAMPLE == 8 && CONST_BITS<=13 && PASS1_BITS<=2
145 28db7fce Michael Niedermayer
#define MULTIPLY(var,const)  MULTIPLY16C16(var,const)
146
#else
147
#define MULTIPLY(var,const)  ((var) * (const))
148
#endif
149
150
151 d43fb4e8 Michael Niedermayer
static always_inline void row_fdct(DCTELEM * data){
152
  int_fast32_t tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
153
  int_fast32_t tmp10, tmp11, tmp12, tmp13;
154
  int_fast32_t z1, z2, z3, z4, z5;
155 28db7fce Michael Niedermayer
  DCTELEM *dataptr;
156
  int ctr;
157
  SHIFT_TEMPS
158
159
  /* Pass 1: process rows. */
160
  /* Note results are scaled up by sqrt(8) compared to a true DCT; */
161
  /* furthermore, we scale the results by 2**PASS1_BITS. */
162
163
  dataptr = data;
164
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
165
    tmp0 = dataptr[0] + dataptr[7];
166
    tmp7 = dataptr[0] - dataptr[7];
167
    tmp1 = dataptr[1] + dataptr[6];
168
    tmp6 = dataptr[1] - dataptr[6];
169
    tmp2 = dataptr[2] + dataptr[5];
170
    tmp5 = dataptr[2] - dataptr[5];
171
    tmp3 = dataptr[3] + dataptr[4];
172
    tmp4 = dataptr[3] - dataptr[4];
173
    
174
    /* Even part per LL&M figure 1 --- note that published figure is faulty;
175
     * rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
176
     */
177
    
178
    tmp10 = tmp0 + tmp3;
179
    tmp13 = tmp0 - tmp3;
180
    tmp11 = tmp1 + tmp2;
181
    tmp12 = tmp1 - tmp2;
182
    
183
    dataptr[0] = (DCTELEM) ((tmp10 + tmp11) << PASS1_BITS);
184
    dataptr[4] = (DCTELEM) ((tmp10 - tmp11) << PASS1_BITS);
185
    
186
    z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
187
    dataptr[2] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
188
                                   CONST_BITS-PASS1_BITS);
189
    dataptr[6] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
190
                                   CONST_BITS-PASS1_BITS);
191
    
192
    /* Odd part per figure 8 --- note paper omits factor of sqrt(2).
193
     * cK represents cos(K*pi/16).
194
     * i0..i3 in the paper are tmp4..tmp7 here.
195
     */
196
    
197
    z1 = tmp4 + tmp7;
198
    z2 = tmp5 + tmp6;
199
    z3 = tmp4 + tmp6;
200
    z4 = tmp5 + tmp7;
201
    z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
202
    
203
    tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
204
    tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
205
    tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
206
    tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
207
    z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
208
    z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
209
    z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
210
    z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
211
    
212
    z3 += z5;
213
    z4 += z5;
214
    
215
    dataptr[7] = (DCTELEM) DESCALE(tmp4 + z1 + z3, CONST_BITS-PASS1_BITS);
216
    dataptr[5] = (DCTELEM) DESCALE(tmp5 + z2 + z4, CONST_BITS-PASS1_BITS);
217
    dataptr[3] = (DCTELEM) DESCALE(tmp6 + z2 + z3, CONST_BITS-PASS1_BITS);
218
    dataptr[1] = (DCTELEM) DESCALE(tmp7 + z1 + z4, CONST_BITS-PASS1_BITS);
219
    
220
    dataptr += DCTSIZE;                /* advance pointer to next row */
221
  }
222 d43fb4e8 Michael Niedermayer
}
223
224
/*
225
 * Perform the forward DCT on one block of samples.
226
 */
227
228
GLOBAL(void)
229
ff_jpeg_fdct_islow (DCTELEM * data)
230
{
231
  int_fast32_t tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
232
  int_fast32_t tmp10, tmp11, tmp12, tmp13;
233
  int_fast32_t z1, z2, z3, z4, z5;
234
  DCTELEM *dataptr;
235
  int ctr;
236
  SHIFT_TEMPS
237
238
  row_fdct(data);
239 28db7fce Michael Niedermayer
240
  /* Pass 2: process columns.
241
   * We remove the PASS1_BITS scaling, but leave the results scaled up
242
   * by an overall factor of 8.
243
   */
244
245
  dataptr = data;
246
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
247
    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
248
    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
249
    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
250
    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
251
    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
252
    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
253
    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
254
    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
255
    
256
    /* Even part per LL&M figure 1 --- note that published figure is faulty;
257
     * rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
258
     */
259
    
260
    tmp10 = tmp0 + tmp3;
261
    tmp13 = tmp0 - tmp3;
262
    tmp11 = tmp1 + tmp2;
263
    tmp12 = tmp1 - tmp2;
264
    
265
    dataptr[DCTSIZE*0] = (DCTELEM) DESCALE(tmp10 + tmp11, PASS1_BITS);
266
    dataptr[DCTSIZE*4] = (DCTELEM) DESCALE(tmp10 - tmp11, PASS1_BITS);
267
    
268
    z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
269
    dataptr[DCTSIZE*2] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
270
                                           CONST_BITS+PASS1_BITS);
271
    dataptr[DCTSIZE*6] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
272
                                           CONST_BITS+PASS1_BITS);
273
    
274
    /* Odd part per figure 8 --- note paper omits factor of sqrt(2).
275
     * cK represents cos(K*pi/16).
276
     * i0..i3 in the paper are tmp4..tmp7 here.
277
     */
278
    
279
    z1 = tmp4 + tmp7;
280
    z2 = tmp5 + tmp6;
281
    z3 = tmp4 + tmp6;
282
    z4 = tmp5 + tmp7;
283
    z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
284
    
285
    tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
286
    tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
287
    tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
288
    tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
289
    z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
290
    z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
291
    z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
292
    z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
293
    
294
    z3 += z5;
295
    z4 += z5;
296
    
297
    dataptr[DCTSIZE*7] = (DCTELEM) DESCALE(tmp4 + z1 + z3,
298
                                           CONST_BITS+PASS1_BITS);
299
    dataptr[DCTSIZE*5] = (DCTELEM) DESCALE(tmp5 + z2 + z4,
300
                                           CONST_BITS+PASS1_BITS);
301
    dataptr[DCTSIZE*3] = (DCTELEM) DESCALE(tmp6 + z2 + z3,
302
                                           CONST_BITS+PASS1_BITS);
303
    dataptr[DCTSIZE*1] = (DCTELEM) DESCALE(tmp7 + z1 + z4,
304
                                           CONST_BITS+PASS1_BITS);
305
    
306
    dataptr++;                        /* advance pointer to next column */
307
  }
308
}
309 10acc479 Roman Shaposhnik
310
/*
311
 * The secret of DCT2-4-8 is really simple -- you do the usual 1-DCT
312
 * on the rows and then, instead of doing even and odd, part on the colums
313
 * you do even part two times.
314
 */
315
GLOBAL(void)
316
ff_fdct248_islow (DCTELEM * data)
317
{
318 d43fb4e8 Michael Niedermayer
  int_fast32_t tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
319
  int_fast32_t tmp10, tmp11, tmp12, tmp13;
320
  int_fast32_t z1;
321 10acc479 Roman Shaposhnik
  DCTELEM *dataptr;
322
  int ctr;
323
  SHIFT_TEMPS
324
325 d43fb4e8 Michael Niedermayer
  row_fdct(data);
326 10acc479 Roman Shaposhnik
327
  /* Pass 2: process columns.
328
   * We remove the PASS1_BITS scaling, but leave the results scaled up
329
   * by an overall factor of 8.
330
   */
331
332
  dataptr = data;
333
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
334
     tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*1];
335
     tmp1 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*3];
336
     tmp2 = dataptr[DCTSIZE*4] + dataptr[DCTSIZE*5];
337
     tmp3 = dataptr[DCTSIZE*6] + dataptr[DCTSIZE*7];
338
     tmp4 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*1];
339
     tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*3];
340
     tmp6 = dataptr[DCTSIZE*4] - dataptr[DCTSIZE*5];
341
     tmp7 = dataptr[DCTSIZE*6] - dataptr[DCTSIZE*7];
342
      
343
     tmp10 = tmp0 + tmp3;
344
     tmp11 = tmp1 + tmp2;
345
     tmp12 = tmp1 - tmp2;
346
     tmp13 = tmp0 - tmp3;
347
     
348
     dataptr[DCTSIZE*0] = (DCTELEM) DESCALE(tmp10 + tmp11, PASS1_BITS);
349
     dataptr[DCTSIZE*4] = (DCTELEM) DESCALE(tmp10 - tmp11, PASS1_BITS);
350
     
351
     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
352
     dataptr[DCTSIZE*2] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
353
                                            CONST_BITS+PASS1_BITS);
354
     dataptr[DCTSIZE*6] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
355
                                            CONST_BITS+PASS1_BITS);
356
357
     tmp10 = tmp4 + tmp7;
358
     tmp11 = tmp5 + tmp6;
359
     tmp12 = tmp5 - tmp6;
360
     tmp13 = tmp4 - tmp7;
361
362
     dataptr[DCTSIZE*1] = (DCTELEM) DESCALE(tmp10 + tmp11, PASS1_BITS);
363
     dataptr[DCTSIZE*5] = (DCTELEM) DESCALE(tmp10 - tmp11, PASS1_BITS);
364
     
365
     z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
366
     dataptr[DCTSIZE*3] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
367
                                            CONST_BITS+PASS1_BITS);
368
     dataptr[DCTSIZE*7] = (DCTELEM) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
369
                                            CONST_BITS+PASS1_BITS);
370
    
371
     dataptr++;                        /* advance pointer to next column */
372
  }
373
}