PeerStreamer

/*

 * 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 <stdlib.h>

#include <string.h>

#include "libavutil/common.h"

#include "libavutil/mathematics.h"

#include "fft.h"

/**

 * @file

 * MDCT/IMDCT transforms.

 */

// Generate a Kaiser-Bessel Derived Window.

#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation

av_cold void ff_kbd_window_init(float *window, float alpha, int n)

{

   int i, j;

   double sum = 0.0, bessel, tmp;

   double local_window[FF_KBD_WINDOW_MAX];

   double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);

   assert(n <= FF_KBD_WINDOW_MAX);

   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);

}

#include "mdct_tablegen.h"

/**

 * init MDCT or IMDCT computation.

 */

av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)

{

    int n, n4, i;

    double alpha, theta;

    int tstep;

    memset(s, 0, sizeof(*s));

    n = 1 << nbits;

    s->mdct_bits = nbits;

    s->mdct_size = n;

    n4 = n >> 2;

    s->mdct_permutation = FF_MDCT_PERM_NONE;

    if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)

        goto fail;

    s->tcos = av_malloc(n/2 * sizeof(FFTSample));

    if (!s->tcos)

        goto fail;

    switch (s->mdct_permutation) {

    case FF_MDCT_PERM_NONE:

        s->tsin = s->tcos + n4;

        tstep = 1;

        break;

    case FF_MDCT_PERM_INTERLEAVE:

        s->tsin = s->tcos + 1;

        tstep = 2;

        break;

    default:

        goto fail;

    }

    theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);

    scale = sqrt(fabs(scale));

    for(i=0;i<n4;i++) {

        alpha = 2 * M_PI * (i + theta) / n;

        s->tcos[i*tstep] = -cos(alpha) * scale;

        s->tsin[i*tstep] = -sin(alpha) * scale;

    }

    return 0;

 fail:

    ff_mdct_end(s);

    return -1;

}

/* complex multiplication: p = a * b */

#define CMUL(pre, pim, are, aim, bre, bim) \

{\

    FFTSample _are = (are);\

    FFTSample _aim = (aim);\

    FFTSample _bre = (bre);\

    FFTSample _bim = (bim);\

    (pre) = _are * _bre - _aim * _bim;\

    (pim) = _are * _bim + _aim * _bre;\

}

/**

 * Compute the middle half of the inverse MDCT of size N = 2^nbits,

 * thus excluding the parts that can be derived by symmetry

 * @param output N/2 samples

 * @param input N/2 samples

 */

void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)

{

    int k, n8, n4, n2, n, j;

    const uint16_t *revtab = s->revtab;

    const FFTSample *tcos = s->tcos;

    const FFTSample *tsin = s->tsin;

    const FFTSample *in1, *in2;

    FFTComplex *z = (FFTComplex *)output;

    n = 1 << s->mdct_bits;

    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, z);

    /* post rotation + reordering */

    for(k = 0; k < n8; k++) {

        FFTSample r0, i0, r1, i1;

        CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);

        CMUL(r1, i0, z[n8+k  ].im, z[n8+k  ].re, tsin[n8+k  ], tcos[n8+k  ]);

        z[n8-k-1].re = r0;

        z[n8-k-1].im = i0;

        z[n8+k  ].re = r1;

        z[n8+k  ].im = i1;

    }

}

/**

 * Compute inverse MDCT of size N = 2^nbits

 * @param output N samples

 * @param input N/2 samples

 */

void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)

{

    int k;

    int n = 1 << s->mdct_bits;

    int n2 = n >> 1;

    int n4 = n >> 2;

    ff_imdct_half_c(s, output+n4, input);

    for(k = 0; k < n4; k++) {

        output[k] = -output[n2-k-1];

        output[n-k-1] = output[n2+k];

    }

}

/**

 * Compute MDCT of size N = 2^nbits

 * @param input N samples

 * @param out N/2 samples

 */

void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input)

{

    int i, j, n, n8, n4, n2, n3;

    FFTSample re, im;

    const uint16_t *revtab = s->revtab;

    const FFTSample *tcos = s->tcos;

    const FFTSample *tsin = s->tsin;

    FFTComplex *x = (FFTComplex *)out;

    n = 1 << s->mdct_bits;

    n2 = n >> 1;

    n4 = n >> 2;

    n8 = n >> 3;

    n3 = 3 * n4;

    /* pre rotation */

    for(i=0;i<n8;i++) {

        re = -input[2*i+n3] - 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, x);

    /* post rotation */

    for(i=0;i<n8;i++) {

        FFTSample r0, i0, r1, i1;

        CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);

        CMUL(i0, r1, x[n8+i  ].re, x[n8+i  ].im, -tsin[n8+i  ], -tcos[n8+i  ]);

        x[n8-i-1].re = r0;

        x[n8-i-1].im = i0;

        x[n8+i  ].re = r1;

        x[n8+i  ].im = i1;

    }

}

av_cold void ff_mdct_end(FFTContext *s)

{

    av_freep(&s->tcos);

    ff_fft_end(s);

}