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118 lines
4.2 KiB
C
Executable File
118 lines
4.2 KiB
C
Executable File
/*
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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 "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) 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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