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mdct.c
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1 /*
2  * MDCT/IMDCT transforms
3  * Copyright (c) 2002 Fabrice Bellard
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 #include <stdlib.h>
23 #include <string.h>
24 #include "libavutil/common.h"
25 #include "libavutil/mathematics.h"
26 #include "fft.h"
27 #include "fft-internal.h"
28 
29 /**
30  * @file
31  * MDCT/IMDCT transforms.
32  */
33 
34 #if CONFIG_FFT_FLOAT
35 # define RSCALE(x) (x)
36 #else
37 #if CONFIG_FFT_FIXED_32
38 # define RSCALE(x) (((x) + 32) >> 6)
39 #else /* CONFIG_FFT_FIXED_32 */
40 # define RSCALE(x) ((x) >> 1)
41 #endif /* CONFIG_FFT_FIXED_32 */
42 #endif
43 
44 /**
45  * init MDCT or IMDCT computation.
46  */
47 av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)
48 {
49  int n, n4, i;
50  double alpha, theta;
51  int tstep;
52 
53  memset(s, 0, sizeof(*s));
54  n = 1 << nbits;
55  s->mdct_bits = nbits;
56  s->mdct_size = n;
57  n4 = n >> 2;
59 
60  if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)
61  goto fail;
62 
63  s->tcos = av_malloc(n/2 * sizeof(FFTSample));
64  if (!s->tcos)
65  goto fail;
66 
67  switch (s->mdct_permutation) {
68  case FF_MDCT_PERM_NONE:
69  s->tsin = s->tcos + n4;
70  tstep = 1;
71  break;
73  s->tsin = s->tcos + 1;
74  tstep = 2;
75  break;
76  default:
77  goto fail;
78  }
79 
80  theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);
81  scale = sqrt(fabs(scale));
82  for(i=0;i<n4;i++) {
83  alpha = 2 * M_PI * (i + theta) / n;
84  s->tcos[i*tstep] = FIX15(-cos(alpha) * scale);
85  s->tsin[i*tstep] = FIX15(-sin(alpha) * scale);
86  }
87  return 0;
88  fail:
89  ff_mdct_end(s);
90  return -1;
91 }
92 
93 /**
94  * Compute the middle half of the inverse MDCT of size N = 2^nbits,
95  * thus excluding the parts that can be derived by symmetry
96  * @param output N/2 samples
97  * @param input N/2 samples
98  */
99 void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)
100 {
101  int k, n8, n4, n2, n, j;
102  const uint16_t *revtab = s->revtab;
103  const FFTSample *tcos = s->tcos;
104  const FFTSample *tsin = s->tsin;
105  const FFTSample *in1, *in2;
106  FFTComplex *z = (FFTComplex *)output;
107 
108  n = 1 << s->mdct_bits;
109  n2 = n >> 1;
110  n4 = n >> 2;
111  n8 = n >> 3;
112 
113  /* pre rotation */
114  in1 = input;
115  in2 = input + n2 - 1;
116  for(k = 0; k < n4; k++) {
117  j=revtab[k];
118  CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
119  in1 += 2;
120  in2 -= 2;
121  }
122  s->fft_calc(s, z);
123 
124  /* post rotation + reordering */
125  for(k = 0; k < n8; k++) {
126  FFTSample r0, i0, r1, i1;
127  CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
128  CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]);
129  z[n8-k-1].re = r0;
130  z[n8-k-1].im = i0;
131  z[n8+k ].re = r1;
132  z[n8+k ].im = i1;
133  }
134 }
135 
136 /**
137  * Compute inverse MDCT of size N = 2^nbits
138  * @param output N samples
139  * @param input N/2 samples
140  */
141 void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)
142 {
143  int k;
144  int n = 1 << s->mdct_bits;
145  int n2 = n >> 1;
146  int n4 = n >> 2;
147 
148  ff_imdct_half_c(s, output+n4, input);
149 
150  for(k = 0; k < n4; k++) {
151  output[k] = -output[n2-k-1];
152  output[n-k-1] = output[n2+k];
153  }
154 }
155 
156 /**
157  * Compute MDCT of size N = 2^nbits
158  * @param input N samples
159  * @param out N/2 samples
160  */
162 {
163  int i, j, n, n8, n4, n2, n3;
164  FFTDouble re, im;
165  const uint16_t *revtab = s->revtab;
166  const FFTSample *tcos = s->tcos;
167  const FFTSample *tsin = s->tsin;
168  FFTComplex *x = (FFTComplex *)out;
169 
170  n = 1 << s->mdct_bits;
171  n2 = n >> 1;
172  n4 = n >> 2;
173  n8 = n >> 3;
174  n3 = 3 * n4;
175 
176  /* pre rotation */
177  for(i=0;i<n8;i++) {
178  re = RSCALE(-input[2*i+n3] - input[n3-1-2*i]);
179  im = RSCALE(-input[n4+2*i] + input[n4-1-2*i]);
180  j = revtab[i];
181  CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
182 
183  re = RSCALE( input[2*i] - input[n2-1-2*i]);
184  im = RSCALE(-input[n2+2*i] - input[ n-1-2*i]);
185  j = revtab[n8 + i];
186  CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
187  }
188 
189  s->fft_calc(s, x);
190 
191  /* post rotation */
192  for(i=0;i<n8;i++) {
193  FFTSample r0, i0, r1, i1;
194  CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
195  CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]);
196  x[n8-i-1].re = r0;
197  x[n8-i-1].im = i0;
198  x[n8+i ].re = r1;
199  x[n8+i ].im = i1;
200  }
201 }
202 
204 {
205  av_freep(&s->tcos);
206  ff_fft_end(s);
207 }