/* * 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 approximationvoid 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;    float 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) \{\    float _are = (are);\    float _aim = (aim);\    float _bre = (bre);\    float _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);}