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);
51 // Generate a sine window.
52 void ff_sine_window_init(float *window, int n) {
54 for(i = 0; i < n; i++)
55 window[i] = sin((i + 0.5) / (2 * n) * M_PI);
59 * init MDCT or IMDCT computation.
61 int ff_mdct_init(MDCTContext *s, int nbits, int inverse)
66 memset(s, 0, sizeof(*s));
71 s->tcos = av_malloc(n4 * sizeof(FFTSample));
74 s->tsin = av_malloc(n4 * sizeof(FFTSample));
79 alpha = 2 * M_PI * (i + 1.0 / 8.0) / n;
80 s->tcos[i] = -cos(alpha);
81 s->tsin[i] = -sin(alpha);
83 if (ff_fft_init(&s->fft, s->nbits - 2, inverse) < 0)
92 /* complex multiplication: p = a * b */
93 #define CMUL(pre, pim, are, aim, bre, bim) \
95 FFTSample _are = (are);\
96 FFTSample _aim = (aim);\
97 FFTSample _bre = (bre);\
98 FFTSample _bim = (bim);\
99 (pre) = _are * _bre - _aim * _bim;\
100 (pim) = _are * _bim + _aim * _bre;\
104 * Compute the middle half of the inverse MDCT of size N = 2^nbits,
105 * thus excluding the parts that can be derived by symmetry
106 * @param output N/2 samples
107 * @param input N/2 samples
109 void ff_imdct_half_c(MDCTContext *s, FFTSample *output, const FFTSample *input)
111 int k, n8, n4, n2, n, j;
112 const uint16_t *revtab = s->fft.revtab;
113 const FFTSample *tcos = s->tcos;
114 const FFTSample *tsin = s->tsin;
115 const FFTSample *in1, *in2;
116 FFTComplex *z = (FFTComplex *)output;
125 in2 = input + n2 - 1;
126 for(k = 0; k < n4; k++) {
128 CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
132 ff_fft_calc(&s->fft, z);
134 /* post rotation + reordering */
136 for(k = 0; k < n8; k++) {
137 FFTSample r0, i0, r1, i1;
138 CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
139 CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]);
148 * Compute inverse MDCT of size N = 2^nbits
149 * @param output N samples
150 * @param input N/2 samples
151 * @param tmp N/2 samples
153 void ff_imdct_calc_c(MDCTContext *s, FFTSample *output, const FFTSample *input)
156 int n = 1 << s->nbits;
160 ff_imdct_half_c(s, output+n4, input);
162 for(k = 0; k < n4; k++) {
163 output[k] = -output[n2-k-1];
164 output[n-k-1] = output[n2+k];
169 * Compute MDCT of size N = 2^nbits
170 * @param input N samples
171 * @param out N/2 samples
172 * @param tmp temporary storage of N/2 samples
174 void ff_mdct_calc(MDCTContext *s, FFTSample *out, const FFTSample *input)
176 int i, j, n, n8, n4, n2, n3;
178 const uint16_t *revtab = s->fft.revtab;
179 const FFTSample *tcos = s->tcos;
180 const FFTSample *tsin = s->tsin;
181 FFTComplex *x = (FFTComplex *)out;
191 re = -input[2*i+3*n4] - input[n3-1-2*i];
192 im = -input[n4+2*i] + input[n4-1-2*i];
194 CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
196 re = input[2*i] - input[n2-1-2*i];
197 im = -(input[n2+2*i] + input[n-1-2*i]);
199 CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
202 ff_fft_calc(&s->fft, x);
206 FFTSample r0, i0, r1, i1;
207 CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
208 CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]);
216 void ff_mdct_end(MDCTContext *s)