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/*
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 * (I)RDFT transforms
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 * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include <math.h>
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#include "libavutil/mathematics.h"
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#include "fft.h"
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/**
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 * @file libavcodec/rdft.c
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 * (Inverse) Real Discrete Fourier Transforms.
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 */
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/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
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#if !CONFIG_HARDCODED_TABLES
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SINTABLE(16);
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SINTABLE(32);
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SINTABLE(64);
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SINTABLE(128);
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SINTABLE(256);
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SINTABLE(512);
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SINTABLE(1024);
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SINTABLE(2048);
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SINTABLE(4096);
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SINTABLE(8192);
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SINTABLE(16384);
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SINTABLE(32768);
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SINTABLE(65536);
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#endif
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SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {
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    NULL, NULL, NULL, NULL,
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    ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024,
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    ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,
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};
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av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
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{
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    int n = 1 << nbits;
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    int i;
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    const double theta = (trans == RDFT || trans == IRIDFT ? -1 : 1)*2*M_PI/n;
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    s->nbits           = nbits;
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    s->inverse         = trans == IRDFT || trans == IRIDFT;
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    s->sign_convention = trans == RIDFT || trans == IRIDFT ? 1 : -1;
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    if (nbits < 4 || nbits > 16)
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        return -1;
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    if (ff_fft_init(&s->fft, nbits-1, trans == IRDFT || trans == RIDFT) < 0)
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        return -1;
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    ff_init_ff_cos_tabs(nbits);
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    s->tcos = ff_cos_tabs[nbits];
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    s->tsin = ff_sin_tabs[nbits]+(trans == RDFT || trans == IRIDFT)*(n>>2);
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#if !CONFIG_HARDCODED_TABLES
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    for (i = 0; i < (n>>2); i++) {
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        s->tsin[i] = sin(i*theta);
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    }
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#endif
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    return 0;
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}
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/** Map one real FFT into two parallel real even and odd FFTs. Then interleave
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 * the two real FFTs into one complex FFT. Unmangle the results.
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 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
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 */
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static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
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{
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    int i, i1, i2;
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    FFTComplex ev, od;
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    const int n = 1 << s->nbits;
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    const float k1 = 0.5;
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    const float k2 = 0.5 - s->inverse;
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    const FFTSample *tcos = s->tcos;
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    const FFTSample *tsin = s->tsin;
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    if (!s->inverse) {
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        ff_fft_permute(&s->fft, (FFTComplex*)data);
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        ff_fft_calc(&s->fft, (FFTComplex*)data);
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    }
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    /* i=0 is a special case because of packing, the DC term is real, so we
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       are going to throw the N/2 term (also real) in with it. */
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    ev.re = data[0];
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    data[0] = ev.re+data[1];
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    data[1] = ev.re-data[1];
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    for (i = 1; i < (n>>2); i++) {
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        i1 = 2*i;
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        i2 = n-i1;
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        /* Separate even and odd FFTs */
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        ev.re =  k1*(data[i1  ]+data[i2  ]);
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        od.im = -k2*(data[i1  ]-data[i2  ]);
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        ev.im =  k1*(data[i1+1]-data[i2+1]);
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        od.re =  k2*(data[i1+1]+data[i2+1]);
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        /* Apply twiddle factors to the odd FFT and add to the even FFT */
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        data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
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        data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
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        data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
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        data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
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    }
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    data[2*i+1]=s->sign_convention*data[2*i+1];
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    if (s->inverse) {
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        data[0] *= k1;
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        data[1] *= k1;
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        ff_fft_permute(&s->fft, (FFTComplex*)data);
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        ff_fft_calc(&s->fft, (FFTComplex*)data);
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    }
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}
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void ff_rdft_calc(RDFTContext *s, FFTSample *data)
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{
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    ff_rdft_calc_c(s, data);
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}
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av_cold void ff_rdft_end(RDFTContext *s)
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{
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    ff_fft_end(&s->fft);
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}