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/*
* (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 "rdft.h"
/**
* @file
* (Inverse) Real Discrete Fourier Transforms.
*/
/** 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 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) {
s->fft.fft_permute(&s->fft, (FFTComplex*)data);
s->fft.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];
#define RDFT_UNMANGLE(sign0, sign1) \
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] sign0 od.im*tsin[i]; \
data[i1+1] = ev.im + od.im*tcos[i] sign1 od.re*tsin[i]; \
data[i2 ] = ev.re - od.re*tcos[i] sign1 od.im*tsin[i]; \
data[i2+1] = -ev.im + od.im*tcos[i] sign1 od.re*tsin[i]; \
}
if (s->negative_sin) {
RDFT_UNMANGLE(+,-)
} else {
RDFT_UNMANGLE(-,+)
}
data[2*i+1]=s->sign_convention*data[2*i+1];
if (s->inverse) {
data[0] *= k1;
data[1] *= k1;
s->fft.fft_permute(&s->fft, (FFTComplex*)data);
s->fft.fft_calc(&s->fft, (FFTComplex*)data);
}
}
av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
{
int n = 1 << nbits;
int ret;
s->nbits = nbits;
s->inverse = trans == IDFT_C2R || trans == DFT_C2R;
s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
s->negative_sin = trans == DFT_C2R || trans == DFT_R2C;
if (nbits < 4 || nbits > 16)
return AVERROR(EINVAL);
if ((ret = ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C)) < 0)
return ret;
ff_init_ff_cos_tabs(nbits);
s->tcos = ff_cos_tabs[nbits];
s->tsin = ff_cos_tabs[nbits] + (n >> 2);
s->rdft_calc = rdft_calc_c;
if (ARCH_ARM) ff_rdft_init_arm(s);
return 0;
}
av_cold void ff_rdft_end(RDFTContext *s)
{
ff_fft_end(&s->fft);
}
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