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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
*/ |
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#include <stdlib.h> |
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#include <math.h> |
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#include "libavutil/mathematics.h" |
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#include "rdft.h" |
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/** |
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* @file |
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* (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
*/ |
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static void rdft_calc_c(RDFTContext *s, FFTSample *data) |
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{
int i, i1, i2; |
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FFTComplex ev, od, odsum; |
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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) { |
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s->fft.fft_permute(&s->fft, (FFTComplex*)data);
s->fft.fft_calc(&s->fft, (FFTComplex*)data); |
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}
/* 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]; |
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#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 ]); \ |
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od.im = k2*(data[i2 ]-data[i1 ]); \ |
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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 */ \ |
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odsum.re = od.re*tcos[i] sign0 od.im*tsin[i]; \
odsum.im = od.im*tcos[i] sign1 od.re*tsin[i]; \
data[i1 ] = ev.re + odsum.re; \
data[i1+1] = ev.im + odsum.im; \
data[i2 ] = ev.re - odsum.re; \
data[i2+1] = odsum.im - ev.im; \ |
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}
if (s->negative_sin) {
RDFT_UNMANGLE(+,-)
} else {
RDFT_UNMANGLE(-,+) |
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} |
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|
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data[2*i+1]=s->sign_convention*data[2*i+1];
if (s->inverse) {
data[0] *= k1;
data[1] *= k1; |
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s->fft.fft_permute(&s->fft, (FFTComplex*)data);
s->fft.fft_calc(&s->fft, (FFTComplex*)data); |
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}
}
|
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av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
{
int n = 1 << nbits; |
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int ret; |
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s->nbits = nbits;
s->inverse = trans == IDFT_C2R || trans == DFT_C2R;
s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1; |
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s->negative_sin = trans == DFT_C2R || trans == DFT_R2C; |
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if (nbits < 4 || nbits > 16) |
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return AVERROR(EINVAL); |
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|
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if ((ret = ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C)) < 0)
return ret; |
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ff_init_ff_cos_tabs(nbits);
s->tcos = ff_cos_tabs[nbits]; |
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s->tsin = ff_cos_tabs[nbits] + (n >> 2); |
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s->rdft_calc = rdft_calc_c; |
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if (ARCH_ARM) ff_rdft_init_arm(s);
|
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return 0;
}
|
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av_cold void ff_rdft_end(RDFTContext *s)
{
ff_fft_end(&s->fft);
} |