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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 <stdlib.h> |
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#include <math.h> |
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#include "libavutil/error.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. |
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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 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, odsum; |
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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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s->fft.fft_permute(&s->fft, (FFTComplex*)data); |
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s->fft.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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#define RDFT_UNMANGLE(sign0, sign1) \ |
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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[i2 ]-data[i1 ]); \ |
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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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odsum.re = od.re*tcos[i] sign0 od.im*tsin[i]; \ |
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odsum.im = od.im*tcos[i] sign1 od.re*tsin[i]; \ |
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data[i1 ] = ev.re + odsum.re; \ |
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data[i1+1] = ev.im + odsum.im; \ |
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data[i2 ] = ev.re - odsum.re; \ |
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data[i2+1] = odsum.im - ev.im; \ |
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} |
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if (s->negative_sin) { |
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RDFT_UNMANGLE(+,-) |
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} else { |
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RDFT_UNMANGLE(-,+) |
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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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s->fft.fft_permute(&s->fft, (FFTComplex*)data); |
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s->fft.fft_calc(&s->fft, (FFTComplex*)data); |
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} |
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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 ret; |
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s->nbits = nbits; |
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s->inverse = trans == IDFT_C2R || trans == DFT_C2R; |
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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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if ((ret = ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C)) < 0) |
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return ret; |
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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_cos_tabs[nbits] + (n >> 2); |
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s->rdft_calc = rdft_calc_c; |
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#if ARCH_ARM |
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ff_rdft_init_arm(s); |
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#endif |
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return 0; |
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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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} |
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