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
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 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);
52 * init MDCT or IMDCT computation.
54 int ff_mdct_init(MDCTContext *s, int nbits, int inverse)
59 memset(s, 0, sizeof(*s));
64 s->tcos = av_malloc(n4 * sizeof(FFTSample));
67 s->tsin = av_malloc(n4 * sizeof(FFTSample));
72 alpha = 2 * M_PI * (i + 1.0 / 8.0) / n;
73 s->tcos[i] = -cos(alpha);
74 s->tsin[i] = -sin(alpha);
76 if (ff_fft_init(&s->fft, s->nbits - 2, inverse) < 0)
85 /* complex multiplication: p = a * b */
86 #define CMUL(pre, pim, are, aim, bre, bim) \
92 (pre) = _are * _bre - _aim * _bim;\
93 (pim) = _are * _bim + _aim * _bre;\
97 * Compute inverse MDCT of size N = 2^nbits
98 * @param output N samples
99 * @param input N/2 samples
100 * @param tmp N/2 samples
102 void ff_imdct_calc(MDCTContext *s, FFTSample *output,
103 const FFTSample *input, FFTSample *tmp)
105 int k, n8, n4, n2, n, j;
106 const uint16_t *revtab = s->fft.revtab;
107 const FFTSample *tcos = s->tcos;
108 const FFTSample *tsin = s->tsin;
109 const FFTSample *in1, *in2;
110 FFTComplex *z = (FFTComplex *)tmp;
119 in2 = input + n2 - 1;
120 for(k = 0; k < n4; k++) {
122 CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
126 ff_fft_calc(&s->fft, z);
128 /* post rotation + reordering */
130 for(k = 0; k < n4; k++) {
131 CMUL(z[k].re, z[k].im, z[k].re, z[k].im, tcos[k], tsin[k]);
133 for(k = 0; k < n8; k++) {
134 output[2*k] = -z[n8 + k].im;
135 output[n2-1-2*k] = z[n8 + k].im;
137 output[2*k+1] = z[n8-1-k].re;
138 output[n2-1-2*k-1] = -z[n8-1-k].re;
140 output[n2 + 2*k]=-z[k+n8].re;
141 output[n-1- 2*k]=-z[k+n8].re;
143 output[n2 + 2*k+1]=z[n8-k-1].im;
144 output[n-2 - 2 * k] = z[n8-k-1].im;
149 * Compute MDCT of size N = 2^nbits
150 * @param input N samples
151 * @param out N/2 samples
152 * @param tmp temporary storage of N/2 samples
154 void ff_mdct_calc(MDCTContext *s, FFTSample *out,
155 const FFTSample *input, FFTSample *tmp)
157 int i, j, n, n8, n4, n2, n3;
158 FFTSample re, im, re1, im1;
159 const uint16_t *revtab = s->fft.revtab;
160 const FFTSample *tcos = s->tcos;
161 const FFTSample *tsin = s->tsin;
162 FFTComplex *x = (FFTComplex *)tmp;
172 re = -input[2*i+3*n4] - input[n3-1-2*i];
173 im = -input[n4+2*i] + input[n4-1-2*i];
175 CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
177 re = input[2*i] - input[n2-1-2*i];
178 im = -(input[n2+2*i] + input[n-1-2*i]);
180 CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
183 ff_fft_calc(&s->fft, x);
189 CMUL(re1, im1, re, im, -tsin[i], -tcos[i]);
195 void ff_mdct_end(MDCTContext *s)