134 lines
4.1 KiB
C
134 lines
4.1 KiB
C
/*
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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/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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/** 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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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 == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n;
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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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if (nbits < 4 || nbits > 16)
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return -1;
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if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 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 == DFT_R2C || trans == DFT_C2R)*(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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s->rdft_calc = ff_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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}
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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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