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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 # define RSCALE(x) ((x) >> 1)
38 #endif
39 
40 /**
41  * init MDCT or IMDCT computation.
42  */
43 av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)
44 {
45  int n, n4, i;
46  double alpha, theta;
47  int tstep;
48 
49  memset(s, 0, sizeof(*s));
50  n = 1 << nbits;
51  s->mdct_bits = nbits;
52  s->mdct_size = n;
53  n4 = n >> 2;
55 
56  if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)
57  goto fail;
58 
59  s->tcos = av_malloc(n/2 * sizeof(FFTSample));
60  if (!s->tcos)
61  goto fail;
62 
63  switch (s->mdct_permutation) {
64  case FF_MDCT_PERM_NONE:
65  s->tsin = s->tcos + n4;
66  tstep = 1;
67  break;
69  s->tsin = s->tcos + 1;
70  tstep = 2;
71  break;
72  default:
73  goto fail;
74  }
75 
76  theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);
77  scale = sqrt(fabs(scale));
78  for(i=0;i<n4;i++) {
79  alpha = 2 * M_PI * (i + theta) / n;
80  s->tcos[i*tstep] = FIX15(-cos(alpha) * scale);
81  s->tsin[i*tstep] = FIX15(-sin(alpha) * scale);
82  }
83  return 0;
84  fail:
85  ff_mdct_end(s);
86  return -1;
87 }
88 
89 /**
90  * Compute the middle half of the inverse MDCT of size N = 2^nbits,
91  * thus excluding the parts that can be derived by symmetry
92  * @param output N/2 samples
93  * @param input N/2 samples
94  */
95 void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)
96 {
97  int k, n8, n4, n2, n, j;
98  const uint16_t *revtab = s->revtab;
99  const FFTSample *tcos = s->tcos;
100  const FFTSample *tsin = s->tsin;
101  const FFTSample *in1, *in2;
102  FFTComplex *z = (FFTComplex *)output;
103 
104  n = 1 << s->mdct_bits;
105  n2 = n >> 1;
106  n4 = n >> 2;
107  n8 = n >> 3;
108 
109  /* pre rotation */
110  in1 = input;
111  in2 = input + n2 - 1;
112  for(k = 0; k < n4; k++) {
113  j=revtab[k];
114  CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
115  in1 += 2;
116  in2 -= 2;
117  }
118  s->fft_calc(s, z);
119 
120  /* post rotation + reordering */
121  for(k = 0; k < n8; k++) {
122  FFTSample r0, i0, r1, i1;
123  CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
124  CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]);
125  z[n8-k-1].re = r0;
126  z[n8-k-1].im = i0;
127  z[n8+k ].re = r1;
128  z[n8+k ].im = i1;
129  }
130 }
131 
132 /**
133  * Compute inverse MDCT of size N = 2^nbits
134  * @param output N samples
135  * @param input N/2 samples
136  */
137 void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)
138 {
139  int k;
140  int n = 1 << s->mdct_bits;
141  int n2 = n >> 1;
142  int n4 = n >> 2;
143 
144  ff_imdct_half_c(s, output+n4, input);
145 
146  for(k = 0; k < n4; k++) {
147  output[k] = -output[n2-k-1];
148  output[n-k-1] = output[n2+k];
149  }
150 }
151 
152 /**
153  * Compute MDCT of size N = 2^nbits
154  * @param input N samples
155  * @param out N/2 samples
156  */
158 {
159  int i, j, n, n8, n4, n2, n3;
160  FFTDouble re, im;
161  const uint16_t *revtab = s->revtab;
162  const FFTSample *tcos = s->tcos;
163  const FFTSample *tsin = s->tsin;
164  FFTComplex *x = (FFTComplex *)out;
165 
166  n = 1 << s->mdct_bits;
167  n2 = n >> 1;
168  n4 = n >> 2;
169  n8 = n >> 3;
170  n3 = 3 * n4;
171 
172  /* pre rotation */
173  for(i=0;i<n8;i++) {
174  re = RSCALE(-input[2*i+n3] - input[n3-1-2*i]);
175  im = RSCALE(-input[n4+2*i] + input[n4-1-2*i]);
176  j = revtab[i];
177  CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
178 
179  re = RSCALE( input[2*i] - input[n2-1-2*i]);
180  im = RSCALE(-input[n2+2*i] - input[ n-1-2*i]);
181  j = revtab[n8 + i];
182  CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
183  }
184 
185  s->fft_calc(s, x);
186 
187  /* post rotation */
188  for(i=0;i<n8;i++) {
189  FFTSample r0, i0, r1, i1;
190  CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
191  CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]);
192  x[n8-i-1].re = r0;
193  x[n8-i-1].im = i0;
194  x[n8+i ].re = r1;
195  x[n8+i ].im = i1;
196  }
197 }
198 
200 {
201  av_freep(&s->tcos);
202  ff_fft_end(s);
203 }