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0780ad9c68
It is redundant with costable. The first half of sintable is identical with the second half of costable. The second half of sintable is negative value of the first half of sintable. The computation is changed to handle sign of sin values, in C code and ARM assembly code. Signed-off-by: Muhammad Faiz <mfcc64@gmail.com>
116 lines
4.0 KiB
C
116 lines
4.0 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 "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;
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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[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] sign0 od.im*tsin[i]; \
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data[i1+1] = ev.im + od.im*tcos[i] sign1 od.re*tsin[i]; \
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data[i2 ] = ev.re - od.re*tcos[i] sign1 od.im*tsin[i]; \
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data[i2+1] = -ev.im + od.im*tcos[i] sign1 od.re*tsin[i]; \
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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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