2 * MDCT/IMDCT transforms
3 * Copyright (c) 2002 Fabrice Bellard
5 * This file is part of FFmpeg.
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.
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.
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
24 * @file libavcodec/mdct.c
25 * MDCT/IMDCT transforms.
28 // Generate a Kaiser-Bessel Derived Window.
29 #define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
30 av_cold void ff_kbd_window_init(float *window, float alpha, int n)
33 double sum = 0.0, bessel, tmp;
34 double local_window[n];
35 double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
37 for (i = 0; i < n; i++) {
38 tmp = i * (n - i) * alpha2;
40 for (j = BESSEL_I0_ITER; j > 0; j--)
41 bessel = bessel * tmp / (j * j) + 1;
43 local_window[i] = sum;
47 for (i = 0; i < n; i++)
48 window[i] = sqrt(local_window[i] / sum);
51 #include "mdct_tablegen.h"
54 * init MDCT or IMDCT computation.
56 av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)
62 memset(s, 0, sizeof(*s));
67 s->permutation = FF_MDCT_PERM_NONE;
69 if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)
72 s->tcos = av_malloc(n/2 * sizeof(FFTSample));
76 switch (s->permutation) {
77 case FF_MDCT_PERM_NONE:
78 s->tsin = s->tcos + n4;
81 case FF_MDCT_PERM_INTERLEAVE:
82 s->tsin = s->tcos + 1;
89 theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);
90 scale = sqrt(fabs(scale));
92 alpha = 2 * M_PI * (i + theta) / n;
93 s->tcos[i*tstep] = -cos(alpha) * scale;
94 s->tsin[i*tstep] = -sin(alpha) * scale;
102 /* complex multiplication: p = a * b */
103 #define CMUL(pre, pim, are, aim, bre, bim) \
105 FFTSample _are = (are);\
106 FFTSample _aim = (aim);\
107 FFTSample _bre = (bre);\
108 FFTSample _bim = (bim);\
109 (pre) = _are * _bre - _aim * _bim;\
110 (pim) = _are * _bim + _aim * _bre;\
114 * Compute the middle half of the inverse MDCT of size N = 2^nbits,
115 * thus excluding the parts that can be derived by symmetry
116 * @param output N/2 samples
117 * @param input N/2 samples
119 void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)
121 int k, n8, n4, n2, n, j;
122 const uint16_t *revtab = s->revtab;
123 const FFTSample *tcos = s->tcos;
124 const FFTSample *tsin = s->tsin;
125 const FFTSample *in1, *in2;
126 FFTComplex *z = (FFTComplex *)output;
128 n = 1 << s->mdct_bits;
135 in2 = input + n2 - 1;
136 for(k = 0; k < n4; k++) {
138 CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
144 /* post rotation + reordering */
145 for(k = 0; k < n8; k++) {
146 FFTSample r0, i0, r1, i1;
147 CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
148 CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]);
157 * Compute inverse MDCT of size N = 2^nbits
158 * @param output N samples
159 * @param input N/2 samples
161 void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)
164 int n = 1 << s->mdct_bits;
168 ff_imdct_half_c(s, output+n4, input);
170 for(k = 0; k < n4; k++) {
171 output[k] = -output[n2-k-1];
172 output[n-k-1] = output[n2+k];
177 * Compute MDCT of size N = 2^nbits
178 * @param input N samples
179 * @param out N/2 samples
181 void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input)
183 int i, j, n, n8, n4, n2, n3;
185 const uint16_t *revtab = s->revtab;
186 const FFTSample *tcos = s->tcos;
187 const FFTSample *tsin = s->tsin;
188 FFTComplex *x = (FFTComplex *)out;
190 n = 1 << s->mdct_bits;
198 re = -input[2*i+3*n4] - input[n3-1-2*i];
199 im = -input[n4+2*i] + input[n4-1-2*i];
201 CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
203 re = input[2*i] - input[n2-1-2*i];
204 im = -(input[n2+2*i] + input[n-1-2*i]);
206 CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
213 FFTSample r0, i0, r1, i1;
214 CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
215 CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]);
223 av_cold void ff_mdct_end(FFTContext *s)