1/* 2 * (I)RDFT transforms 3 * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com> 4 * 5 * This file is part of FFmpeg. 6 * 7 * FFmpeg is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation; either 10 * version 2.1 of the License, or (at your option) any later version. 11 * 12 * FFmpeg is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with FFmpeg; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21#include <stdlib.h> 22#include <math.h> 23#include "libavutil/error.h" 24#include "libavutil/mathematics.h" 25#include "rdft.h" 26 27/** 28 * @file 29 * (Inverse) Real Discrete Fourier Transforms. 30 */ 31 32/** Map one real FFT into two parallel real even and odd FFTs. Then interleave 33 * the two real FFTs into one complex FFT. Unmangle the results. 34 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM 35 */ 36static void rdft_calc_c(RDFTContext *s, FFTSample *data) 37{ 38 int i, i1, i2; 39 FFTComplex ev, od, odsum; 40 const int n = 1 << s->nbits; 41 const float k1 = 0.5; 42 const float k2 = 0.5 - s->inverse; 43 const FFTSample *tcos = s->tcos; 44 const FFTSample *tsin = s->tsin; 45 46 if (!s->inverse) { 47 s->fft.fft_permute(&s->fft, (FFTComplex*)data); 48 s->fft.fft_calc(&s->fft, (FFTComplex*)data); 49 } 50 /* i=0 is a special case because of packing, the DC term is real, so we 51 are going to throw the N/2 term (also real) in with it. */ 52 ev.re = data[0]; 53 data[0] = ev.re+data[1]; 54 data[1] = ev.re-data[1]; 55 56#define RDFT_UNMANGLE(sign0, sign1) \ 57 for (i = 1; i < (n>>2); i++) { \ 58 i1 = 2*i; \ 59 i2 = n-i1; \ 60 /* Separate even and odd FFTs */ \ 61 ev.re = k1*(data[i1 ]+data[i2 ]); \ 62 od.im = k2*(data[i2 ]-data[i1 ]); \ 63 ev.im = k1*(data[i1+1]-data[i2+1]); \ 64 od.re = k2*(data[i1+1]+data[i2+1]); \ 65 /* Apply twiddle factors to the odd FFT and add to the even FFT */ \ 66 odsum.re = od.re*tcos[i] sign0 od.im*tsin[i]; \ 67 odsum.im = od.im*tcos[i] sign1 od.re*tsin[i]; \ 68 data[i1 ] = ev.re + odsum.re; \ 69 data[i1+1] = ev.im + odsum.im; \ 70 data[i2 ] = ev.re - odsum.re; \ 71 data[i2+1] = odsum.im - ev.im; \ 72 } 73 74 if (s->negative_sin) { 75 RDFT_UNMANGLE(+,-) 76 } else { 77 RDFT_UNMANGLE(-,+) 78 } 79 80 data[2*i+1]=s->sign_convention*data[2*i+1]; 81 if (s->inverse) { 82 data[0] *= k1; 83 data[1] *= k1; 84 s->fft.fft_permute(&s->fft, (FFTComplex*)data); 85 s->fft.fft_calc(&s->fft, (FFTComplex*)data); 86 } 87} 88 89av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans) 90{ 91 int n = 1 << nbits; 92 int ret; 93 94 s->nbits = nbits; 95 s->inverse = trans == IDFT_C2R || trans == DFT_C2R; 96 s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1; 97 s->negative_sin = trans == DFT_C2R || trans == DFT_R2C; 98 99 if (nbits < 4 || nbits > 16) 100 return AVERROR(EINVAL); 101 102 if ((ret = ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C)) < 0) 103 return ret; 104 105 ff_init_ff_cos_tabs(nbits); 106 s->tcos = ff_cos_tabs[nbits]; 107 s->tsin = ff_cos_tabs[nbits] + (n >> 2); 108 s->rdft_calc = rdft_calc_c; 109 110#if ARCH_ARM 111 ff_rdft_init_arm(s); 112#endif 113 114 return 0; 115} 116 117av_cold void ff_rdft_end(RDFTContext *s) 118{ 119 ff_fft_end(&s->fft); 120} 121