/* * MDCT/IMDCT transforms * Copyright (c) 2002 Fabrice Bellard. * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include "dsputil.h" /** * @file mdct.c * MDCT/IMDCT transforms. */ // Generate a Kaiser-Bessel Derived Window. #define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation void ff_kbd_window_init(float *window, float alpha, int n) { int i, j; double sum = 0.0, bessel, tmp; double local_window[n]; double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n); for (i = 0; i < n; i++) { tmp = i * (n - i) * alpha2; bessel = 1.0; for (j = BESSEL_I0_ITER; j > 0; j--) bessel = bessel * tmp / (j * j) + 1; sum += bessel; local_window[i] = sum; } sum++; for (i = 0; i < n; i++) window[i] = sqrt(local_window[i] / sum); } /** * init MDCT or IMDCT computation. */ int ff_mdct_init(MDCTContext *s, int nbits, int inverse) { int n, n4, i; double alpha; memset(s, 0, sizeof(*s)); n = 1 << nbits; s->nbits = nbits; s->n = n; n4 = n >> 2; s->tcos = av_malloc(n4 * sizeof(FFTSample)); if (!s->tcos) goto fail; s->tsin = av_malloc(n4 * sizeof(FFTSample)); if (!s->tsin) goto fail; for(i=0;i<n4;i++) { alpha = 2 * M_PI * (i + 1.0 / 8.0) / n; s->tcos[i] = -cos(alpha); s->tsin[i] = -sin(alpha); } if (ff_fft_init(&s->fft, s->nbits - 2, inverse) < 0) goto fail; return 0; fail: av_freep(&s->tcos); av_freep(&s->tsin); return -1; } /* complex multiplication: p = a * b */ #define CMUL(pre, pim, are, aim, bre, bim) \ {\ double _are = (are);\ double _aim = (aim);\ double _bre = (bre);\ double _bim = (bim);\ (pre) = _are * _bre - _aim * _bim;\ (pim) = _are * _bim + _aim * _bre;\ } /** * Compute inverse MDCT of size N = 2^nbits * @param output N samples * @param input N/2 samples * @param tmp N/2 samples */ void ff_imdct_calc(MDCTContext *s, FFTSample *output, const FFTSample *input, FFTSample *tmp) { int k, n8, n4, n2, n, j; const uint16_t *revtab = s->fft.revtab; const FFTSample *tcos = s->tcos; const FFTSample *tsin = s->tsin; const FFTSample *in1, *in2; FFTComplex *z = (FFTComplex *)tmp; n = 1 << s->nbits; n2 = n >> 1; n4 = n >> 2; n8 = n >> 3; /* pre rotation */ in1 = input; in2 = input + n2 - 1; for(k = 0; k < n4; k++) { j=revtab[k]; CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]); in1 += 2; in2 -= 2; } ff_fft_calc(&s->fft, z); /* post rotation + reordering */ /* XXX: optimize */ for(k = 0; k < n4; k++) { CMUL(z[k].re, z[k].im, z[k].re, z[k].im, tcos[k], tsin[k]); } for(k = 0; k < n8; k++) { output[2*k] = -z[n8 + k].im; output[n2-1-2*k] = z[n8 + k].im; output[2*k+1] = z[n8-1-k].re; output[n2-1-2*k-1] = -z[n8-1-k].re; output[n2 + 2*k]=-z[k+n8].re; output[n-1- 2*k]=-z[k+n8].re; output[n2 + 2*k+1]=z[n8-k-1].im; output[n-2 - 2 * k] = z[n8-k-1].im; } } /** * Compute MDCT of size N = 2^nbits * @param input N samples * @param out N/2 samples * @param tmp temporary storage of N/2 samples */ void ff_mdct_calc(MDCTContext *s, FFTSample *out, const FFTSample *input, FFTSample *tmp) { int i, j, n, n8, n4, n2, n3; FFTSample re, im, re1, im1; const uint16_t *revtab = s->fft.revtab; const FFTSample *tcos = s->tcos; const FFTSample *tsin = s->tsin; FFTComplex *x = (FFTComplex *)tmp; n = 1 << s->nbits; n2 = n >> 1; n4 = n >> 2; n8 = n >> 3; n3 = 3 * n4; /* pre rotation */ for(i=0;i<n8;i++) { re = -input[2*i+3*n4] - input[n3-1-2*i]; im = -input[n4+2*i] + input[n4-1-2*i]; j = revtab[i]; CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]); re = input[2*i] - input[n2-1-2*i]; im = -(input[n2+2*i] + input[n-1-2*i]); j = revtab[n8 + i]; CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]); } ff_fft_calc(&s->fft, x); /* post rotation */ for(i=0;i<n4;i++) { re = x[i].re; im = x[i].im; CMUL(re1, im1, re, im, -tsin[i], -tcos[i]); out[2*i] = im1; out[n2-1-2*i] = re1; } } void ff_mdct_end(MDCTContext *s) { av_freep(&s->tcos); av_freep(&s->tsin); ff_fft_end(&s->fft); }