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fft.c
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1 /*
2  * FFT/IFFT transforms
3  * Copyright (c) 2008 Loren Merritt
4  * Copyright (c) 2002 Fabrice Bellard
5  * Partly based on libdjbfft by D. J. Bernstein
6  *
7  * This file is part of FFmpeg.
8  *
9  * FFmpeg is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU Lesser General Public
11  * License as published by the Free Software Foundation; either
12  * version 2.1 of the License, or (at your option) any later version.
13  *
14  * FFmpeg is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17  * Lesser General Public License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public
20  * License along with FFmpeg; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22  */
23 
24 /**
25  * @file
26  * FFT/IFFT transforms.
27  */
28 
29 #include <stdlib.h>
30 #include <string.h>
31 #include "libavutil/mathematics.h"
32 #include "fft.h"
33 #include "fft-internal.h"
34 
35 /* cos(2*pi*x/n) for 0<=x<=n/4, followed by its reverse */
36 #if !CONFIG_HARDCODED_TABLES
37 COSTABLE(16);
38 COSTABLE(32);
39 COSTABLE(64);
40 COSTABLE(128);
41 COSTABLE(256);
42 COSTABLE(512);
43 COSTABLE(1024);
44 COSTABLE(2048);
45 COSTABLE(4096);
46 COSTABLE(8192);
47 COSTABLE(16384);
48 COSTABLE(32768);
49 COSTABLE(65536);
50 #endif
51 COSTABLE_CONST FFTSample * const FFT_NAME(ff_cos_tabs)[] = {
52  NULL, NULL, NULL, NULL,
53  FFT_NAME(ff_cos_16),
54  FFT_NAME(ff_cos_32),
55  FFT_NAME(ff_cos_64),
56  FFT_NAME(ff_cos_128),
57  FFT_NAME(ff_cos_256),
58  FFT_NAME(ff_cos_512),
59  FFT_NAME(ff_cos_1024),
60  FFT_NAME(ff_cos_2048),
61  FFT_NAME(ff_cos_4096),
62  FFT_NAME(ff_cos_8192),
63  FFT_NAME(ff_cos_16384),
64  FFT_NAME(ff_cos_32768),
65  FFT_NAME(ff_cos_65536),
66 };
67 
68 static void ff_fft_permute_c(FFTContext *s, FFTComplex *z);
69 static void ff_fft_calc_c(FFTContext *s, FFTComplex *z);
70 
71 static int split_radix_permutation(int i, int n, int inverse)
72 {
73  int m;
74  if(n <= 2) return i&1;
75  m = n >> 1;
76  if(!(i&m)) return split_radix_permutation(i, m, inverse)*2;
77  m >>= 1;
78  if(inverse == !(i&m)) return split_radix_permutation(i, m, inverse)*4 + 1;
79  else return split_radix_permutation(i, m, inverse)*4 - 1;
80 }
81 
83 {
84 #if !CONFIG_HARDCODED_TABLES
85  int i;
86  int m = 1<<index;
87  double freq = 2*M_PI/m;
88  FFTSample *tab = FFT_NAME(ff_cos_tabs)[index];
89  for(i=0; i<=m/4; i++)
90  tab[i] = FIX15(cos(i*freq));
91  for(i=1; i<m/4; i++)
92  tab[m/2-i] = tab[i];
93 #endif
94 }
95 
96 static const int avx_tab[] = {
97  0, 4, 1, 5, 8, 12, 9, 13, 2, 6, 3, 7, 10, 14, 11, 15
98 };
99 
100 static int is_second_half_of_fft32(int i, int n)
101 {
102  if (n <= 32)
103  return i >= 16;
104  else if (i < n/2)
105  return is_second_half_of_fft32(i, n/2);
106  else if (i < 3*n/4)
107  return is_second_half_of_fft32(i - n/2, n/4);
108  else
109  return is_second_half_of_fft32(i - 3*n/4, n/4);
110 }
111 
113 {
114  int i;
115  int n = 1 << s->nbits;
116 
117  for (i = 0; i < n; i += 16) {
118  int k;
119  if (is_second_half_of_fft32(i, n)) {
120  for (k = 0; k < 16; k++)
121  s->revtab[-split_radix_permutation(i + k, n, s->inverse) & (n - 1)] =
122  i + avx_tab[k];
123 
124  } else {
125  for (k = 0; k < 16; k++) {
126  int j = i + k;
127  j = (j & ~7) | ((j >> 1) & 3) | ((j << 2) & 4);
128  s->revtab[-split_radix_permutation(i + k, n, s->inverse) & (n - 1)] = j;
129  }
130  }
131  }
132 }
133 
134 av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
135 {
136  int i, j, n;
137 
138  if (nbits < 2 || nbits > 16)
139  goto fail;
140  s->nbits = nbits;
141  n = 1 << nbits;
142 
143  s->revtab = av_malloc(n * sizeof(uint16_t));
144  if (!s->revtab)
145  goto fail;
146  s->tmp_buf = av_malloc(n * sizeof(FFTComplex));
147  if (!s->tmp_buf)
148  goto fail;
149  s->inverse = inverse;
151 
153  s->fft_calc = ff_fft_calc_c;
154 #if CONFIG_MDCT
158 #endif
159 
160 #if CONFIG_FFT_FLOAT
161  if (ARCH_ARM) ff_fft_init_arm(s);
162  if (HAVE_ALTIVEC) ff_fft_init_altivec(s);
163  if (ARCH_X86) ff_fft_init_x86(s);
164  if (CONFIG_MDCT) s->mdct_calcw = s->mdct_calc;
165  if (HAVE_MIPSFPU) ff_fft_init_mips(s);
166 #else
167  if (CONFIG_MDCT) s->mdct_calcw = ff_mdct_calcw_c;
168  if (ARCH_ARM) ff_fft_fixed_init_arm(s);
169 #endif
170 
171  for(j=4; j<=nbits; j++) {
173  }
174 
175  if (s->fft_permutation == FF_FFT_PERM_AVX) {
176  fft_perm_avx(s);
177  } else {
178  for(i=0; i<n; i++) {
179  int j = i;
181  j = (j&~3) | ((j>>1)&1) | ((j<<1)&2);
182  s->revtab[-split_radix_permutation(i, n, s->inverse) & (n-1)] = j;
183  }
184  }
185 
186  return 0;
187  fail:
188  av_freep(&s->revtab);
189  av_freep(&s->tmp_buf);
190  return -1;
191 }
192 
194 {
195  int j, np;
196  const uint16_t *revtab = s->revtab;
197  np = 1 << s->nbits;
198  /* TODO: handle split-radix permute in a more optimal way, probably in-place */
199  for(j=0;j<np;j++) s->tmp_buf[revtab[j]] = z[j];
200  memcpy(z, s->tmp_buf, np * sizeof(FFTComplex));
201 }
202 
204 {
205  av_freep(&s->revtab);
206  av_freep(&s->tmp_buf);
207 }
208 
209 #define BUTTERFLIES(a0,a1,a2,a3) {\
210  BF(t3, t5, t5, t1);\
211  BF(a2.re, a0.re, a0.re, t5);\
212  BF(a3.im, a1.im, a1.im, t3);\
213  BF(t4, t6, t2, t6);\
214  BF(a3.re, a1.re, a1.re, t4);\
215  BF(a2.im, a0.im, a0.im, t6);\
216 }
217 
218 // force loading all the inputs before storing any.
219 // this is slightly slower for small data, but avoids store->load aliasing
220 // for addresses separated by large powers of 2.
221 #define BUTTERFLIES_BIG(a0,a1,a2,a3) {\
222  FFTSample r0=a0.re, i0=a0.im, r1=a1.re, i1=a1.im;\
223  BF(t3, t5, t5, t1);\
224  BF(a2.re, a0.re, r0, t5);\
225  BF(a3.im, a1.im, i1, t3);\
226  BF(t4, t6, t2, t6);\
227  BF(a3.re, a1.re, r1, t4);\
228  BF(a2.im, a0.im, i0, t6);\
229 }
230 
231 #define TRANSFORM(a0,a1,a2,a3,wre,wim) {\
232  CMUL(t1, t2, a2.re, a2.im, wre, -wim);\
233  CMUL(t5, t6, a3.re, a3.im, wre, wim);\
234  BUTTERFLIES(a0,a1,a2,a3)\
235 }
236 
237 #define TRANSFORM_ZERO(a0,a1,a2,a3) {\
238  t1 = a2.re;\
239  t2 = a2.im;\
240  t5 = a3.re;\
241  t6 = a3.im;\
242  BUTTERFLIES(a0,a1,a2,a3)\
243 }
244 
245 /* z[0...8n-1], w[1...2n-1] */
246 #define PASS(name)\
247 static void name(FFTComplex *z, const FFTSample *wre, unsigned int n)\
248 {\
249  FFTDouble t1, t2, t3, t4, t5, t6;\
250  int o1 = 2*n;\
251  int o2 = 4*n;\
252  int o3 = 6*n;\
253  const FFTSample *wim = wre+o1;\
254  n--;\
255 \
256  TRANSFORM_ZERO(z[0],z[o1],z[o2],z[o3]);\
257  TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
258  do {\
259  z += 2;\
260  wre += 2;\
261  wim -= 2;\
262  TRANSFORM(z[0],z[o1],z[o2],z[o3],wre[0],wim[0]);\
263  TRANSFORM(z[1],z[o1+1],z[o2+1],z[o3+1],wre[1],wim[-1]);\
264  } while(--n);\
265 }
266 
267 PASS(pass)
268 #undef BUTTERFLIES
269 #define BUTTERFLIES BUTTERFLIES_BIG
270 PASS(pass_big)
271 
272 #define DECL_FFT(n,n2,n4)\
273 static void fft##n(FFTComplex *z)\
274 {\
275  fft##n2(z);\
276  fft##n4(z+n4*2);\
277  fft##n4(z+n4*3);\
278  pass(z,FFT_NAME(ff_cos_##n),n4/2);\
279 }
280 
281 static void fft4(FFTComplex *z)
282 {
283  FFTDouble t1, t2, t3, t4, t5, t6, t7, t8;
284 
285  BF(t3, t1, z[0].re, z[1].re);
286  BF(t8, t6, z[3].re, z[2].re);
287  BF(z[2].re, z[0].re, t1, t6);
288  BF(t4, t2, z[0].im, z[1].im);
289  BF(t7, t5, z[2].im, z[3].im);
290  BF(z[3].im, z[1].im, t4, t8);
291  BF(z[3].re, z[1].re, t3, t7);
292  BF(z[2].im, z[0].im, t2, t5);
293 }
294 
295 static void fft8(FFTComplex *z)
296 {
297  FFTDouble t1, t2, t3, t4, t5, t6;
298 
299  fft4(z);
300 
301  BF(t1, z[5].re, z[4].re, -z[5].re);
302  BF(t2, z[5].im, z[4].im, -z[5].im);
303  BF(t5, z[7].re, z[6].re, -z[7].re);
304  BF(t6, z[7].im, z[6].im, -z[7].im);
305 
306  BUTTERFLIES(z[0],z[2],z[4],z[6]);
307  TRANSFORM(z[1],z[3],z[5],z[7],sqrthalf,sqrthalf);
308 }
309 
310 #if !CONFIG_SMALL
311 static void fft16(FFTComplex *z)
312 {
313  FFTDouble t1, t2, t3, t4, t5, t6;
314  FFTSample cos_16_1 = FFT_NAME(ff_cos_16)[1];
315  FFTSample cos_16_3 = FFT_NAME(ff_cos_16)[3];
316 
317  fft8(z);
318  fft4(z+8);
319  fft4(z+12);
320 
321  TRANSFORM_ZERO(z[0],z[4],z[8],z[12]);
322  TRANSFORM(z[2],z[6],z[10],z[14],sqrthalf,sqrthalf);
323  TRANSFORM(z[1],z[5],z[9],z[13],cos_16_1,cos_16_3);
324  TRANSFORM(z[3],z[7],z[11],z[15],cos_16_3,cos_16_1);
325 }
326 #else
327 DECL_FFT(16,8,4)
328 #endif
329 DECL_FFT(32,16,8)
330 DECL_FFT(64,32,16)
331 DECL_FFT(128,64,32)
332 DECL_FFT(256,128,64)
333 DECL_FFT(512,256,128)
334 #if !CONFIG_SMALL
335 #define pass pass_big
336 #endif
337 DECL_FFT(1024,512,256)
338 DECL_FFT(2048,1024,512)
339 DECL_FFT(4096,2048,1024)
340 DECL_FFT(8192,4096,2048)
341 DECL_FFT(16384,8192,4096)
342 DECL_FFT(32768,16384,8192)
343 DECL_FFT(65536,32768,16384)
344 
345 static void (* const fft_dispatch[])(FFTComplex*) = {
346  fft4, fft8, fft16, fft32, fft64, fft128, fft256, fft512, fft1024,
347  fft2048, fft4096, fft8192, fft16384, fft32768, fft65536,
348 };
349 
351 {
352  fft_dispatch[s->nbits-2](z);
353 }