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/mathematics.h" 24#include "fft.h" 25 26/** 27 * @file 28 * (Inverse) Real Discrete Fourier Transforms. 29 */ 30 31/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */ 32#if !CONFIG_HARDCODED_TABLES 33SINTABLE(16); 34SINTABLE(32); 35SINTABLE(64); 36SINTABLE(128); 37SINTABLE(256); 38SINTABLE(512); 39SINTABLE(1024); 40SINTABLE(2048); 41SINTABLE(4096); 42SINTABLE(8192); 43SINTABLE(16384); 44SINTABLE(32768); 45SINTABLE(65536); 46#endif 47SINTABLE_CONST FFTSample * const ff_sin_tabs[] = { 48 NULL, NULL, NULL, NULL, 49 ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024, 50 ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536, 51}; 52 53/** Map one real FFT into two parallel real even and odd FFTs. Then interleave 54 * the two real FFTs into one complex FFT. Unmangle the results. 55 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM 56 */ 57static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data) 58{ 59 int i, i1, i2; 60 FFTComplex ev, od; 61 const int n = 1 << s->nbits; 62 const float k1 = 0.5; 63 const float k2 = 0.5 - s->inverse; 64 const FFTSample *tcos = s->tcos; 65 const FFTSample *tsin = s->tsin; 66 67 if (!s->inverse) { 68 ff_fft_permute(&s->fft, (FFTComplex*)data); 69 ff_fft_calc(&s->fft, (FFTComplex*)data); 70 } 71 /* i=0 is a special case because of packing, the DC term is real, so we 72 are going to throw the N/2 term (also real) in with it. */ 73 ev.re = data[0]; 74 data[0] = ev.re+data[1]; 75 data[1] = ev.re-data[1]; 76 for (i = 1; i < (n>>2); i++) { 77 i1 = 2*i; 78 i2 = n-i1; 79 /* Separate even and odd FFTs */ 80 ev.re = k1*(data[i1 ]+data[i2 ]); 81 od.im = -k2*(data[i1 ]-data[i2 ]); 82 ev.im = k1*(data[i1+1]-data[i2+1]); 83 od.re = k2*(data[i1+1]+data[i2+1]); 84 /* Apply twiddle factors to the odd FFT and add to the even FFT */ 85 data[i1 ] = ev.re + od.re*tcos[i] - od.im*tsin[i]; 86 data[i1+1] = ev.im + od.im*tcos[i] + od.re*tsin[i]; 87 data[i2 ] = ev.re - od.re*tcos[i] + od.im*tsin[i]; 88 data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i]; 89 } 90 data[2*i+1]=s->sign_convention*data[2*i+1]; 91 if (s->inverse) { 92 data[0] *= k1; 93 data[1] *= k1; 94 ff_fft_permute(&s->fft, (FFTComplex*)data); 95 ff_fft_calc(&s->fft, (FFTComplex*)data); 96 } 97} 98 99av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans) 100{ 101 int n = 1 << nbits; 102 int i; 103 const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n; 104 105 s->nbits = nbits; 106 s->inverse = trans == IDFT_C2R || trans == DFT_C2R; 107 s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1; 108 109 if (nbits < 4 || nbits > 16) 110 return -1; 111 112 if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 0) 113 return -1; 114 115 ff_init_ff_cos_tabs(nbits); 116 s->tcos = ff_cos_tabs[nbits]; 117 s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2); 118#if !CONFIG_HARDCODED_TABLES 119 for (i = 0; i < (n>>2); i++) { 120 s->tsin[i] = sin(i*theta); 121 } 122#endif 123 s->rdft_calc = ff_rdft_calc_c; 124 125 if (ARCH_ARM) ff_rdft_init_arm(s); 126 127 return 0; 128} 129 130av_cold void ff_rdft_end(RDFTContext *s) 131{ 132 ff_fft_end(&s->fft); 133} 134