PeerStreamer

/*

 * (I)RDFT transforms

 * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>

 *

 * 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 <math.h>

#include "libavutil/mathematics.h"

#include "fft.h"

/**

 * @file libavcodec/rdft.c

 * (Inverse) Real Discrete Fourier Transforms.

 */

/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */

#if !CONFIG_HARDCODED_TABLES

SINTABLE(16);

SINTABLE(32);

SINTABLE(64);

SINTABLE(128);

SINTABLE(256);

SINTABLE(512);

SINTABLE(1024);

SINTABLE(2048);

SINTABLE(4096);

SINTABLE(8192);

SINTABLE(16384);

SINTABLE(32768);

SINTABLE(65536);

#endif

SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {

    NULL, NULL, NULL, NULL,

    ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024,

    ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,

};

static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data);

av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)

{

    int n = 1 << nbits;

    int i;

    const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n;

    s->nbits           = nbits;

    s->inverse         = trans == IDFT_C2R || trans == DFT_C2R;

    s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;

    if (nbits < 4 || nbits > 16)

        return -1;

    if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 0)

        return -1;

    ff_init_ff_cos_tabs(nbits);

    s->tcos = ff_cos_tabs[nbits];

    s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2);

#if !CONFIG_HARDCODED_TABLES

    for (i = 0; i < (n>>2); i++) {

        s->tsin[i] = sin(i*theta);

    }

#endif

    s->rdft_calc   = ff_rdft_calc_c;

    return 0;

}

/** Map one real FFT into two parallel real even and odd FFTs. Then interleave

 * the two real FFTs into one complex FFT. Unmangle the results.

 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM

 */

static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)

{

    int i, i1, i2;

    FFTComplex ev, od;

    const int n = 1 << s->nbits;

    const float k1 = 0.5;

    const float k2 = 0.5 - s->inverse;

    const FFTSample *tcos = s->tcos;

    const FFTSample *tsin = s->tsin;

    if (!s->inverse) {

        ff_fft_permute(&s->fft, (FFTComplex*)data);

        ff_fft_calc(&s->fft, (FFTComplex*)data);

    }

    /* i=0 is a special case because of packing, the DC term is real, so we

       are going to throw the N/2 term (also real) in with it. */

    ev.re = data[0];

    data[0] = ev.re+data[1];

    data[1] = ev.re-data[1];

    for (i = 1; i < (n>>2); i++) {

        i1 = 2*i;

        i2 = n-i1;

        /* Separate even and odd FFTs */

        ev.re =  k1*(data[i1  ]+data[i2  ]);

        od.im = -k2*(data[i1  ]-data[i2  ]);

        ev.im =  k1*(data[i1+1]-data[i2+1]);

        od.re =  k2*(data[i1+1]+data[i2+1]);

        /* Apply twiddle factors to the odd FFT and add to the even FFT */

        data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];

        data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];

        data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];

        data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];

    }

    data[2*i+1]=s->sign_convention*data[2*i+1];

    if (s->inverse) {

        data[0] *= k1;

        data[1] *= k1;

        ff_fft_permute(&s->fft, (FFTComplex*)data);

        ff_fft_calc(&s->fft, (FFTComplex*)data);

    }

}

av_cold void ff_rdft_end(RDFTContext *s)

{

    ff_fft_end(&s->fft);

}