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libavcodec/rdft.c

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00001 /*
00002  * (I)RDFT transforms
00003  * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
00004  *
00005  * This file is part of FFmpeg.
00006  *
00007  * FFmpeg is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * FFmpeg is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with FFmpeg; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 #include <math.h>
00022 #include "dsputil.h"
00023 
00029 /* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
00030 DECLARE_ALIGNED_16(FFTSample, ff_sin_16[8]);
00031 DECLARE_ALIGNED_16(FFTSample, ff_sin_32[16]);
00032 DECLARE_ALIGNED_16(FFTSample, ff_sin_64[32]);
00033 DECLARE_ALIGNED_16(FFTSample, ff_sin_128[64]);
00034 DECLARE_ALIGNED_16(FFTSample, ff_sin_256[128]);
00035 DECLARE_ALIGNED_16(FFTSample, ff_sin_512[256]);
00036 DECLARE_ALIGNED_16(FFTSample, ff_sin_1024[512]);
00037 DECLARE_ALIGNED_16(FFTSample, ff_sin_2048[1024]);
00038 DECLARE_ALIGNED_16(FFTSample, ff_sin_4096[2048]);
00039 DECLARE_ALIGNED_16(FFTSample, ff_sin_8192[4096]);
00040 DECLARE_ALIGNED_16(FFTSample, ff_sin_16384[8192]);
00041 DECLARE_ALIGNED_16(FFTSample, ff_sin_32768[16384]);
00042 DECLARE_ALIGNED_16(FFTSample, ff_sin_65536[32768]);
00043 FFTSample *ff_sin_tabs[] = {
00044     ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024,
00045     ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,
00046 };
00047 
00048 av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
00049 {
00050     int n = 1 << nbits;
00051     int i;
00052     const double theta = (trans == RDFT || trans == IRIDFT ? -1 : 1)*2*M_PI/n;
00053 
00054     s->nbits           = nbits;
00055     s->inverse         = trans == IRDFT || trans == IRIDFT;
00056     s->sign_convention = trans == RIDFT || trans == IRIDFT ? 1 : -1;
00057 
00058     if (nbits < 4 || nbits > 16)
00059         return -1;
00060 
00061     if (ff_fft_init(&s->fft, nbits-1, trans == IRDFT || trans == RIDFT) < 0)
00062         return -1;
00063 
00064     s->tcos = ff_cos_tabs[nbits-4];
00065     s->tsin = ff_sin_tabs[nbits-4]+(trans == RDFT || trans == IRIDFT)*(n>>2);
00066     for (i = 0; i < (n>>2); i++) {
00067         s->tcos[i] = cos(i*theta);
00068         s->tsin[i] = sin(i*theta);
00069     }
00070     return 0;
00071 }
00072 
00077 void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
00078 {
00079     int i, i1, i2;
00080     FFTComplex ev, od;
00081     const int n = 1 << s->nbits;
00082     const float k1 = 0.5;
00083     const float k2 = 0.5 - s->inverse;
00084     const FFTSample *tcos = s->tcos;
00085     const FFTSample *tsin = s->tsin;
00086 
00087     if (!s->inverse) {
00088         ff_fft_permute(&s->fft, (FFTComplex*)data);
00089         ff_fft_calc(&s->fft, (FFTComplex*)data);
00090     }
00091     /* i=0 is a special case because of packing, the DC term is real, so we
00092        are going to throw the N/2 term (also real) in with it. */
00093     ev.re = data[0];
00094     data[0] = ev.re+data[1];
00095     data[1] = ev.re-data[1];
00096     for (i = 1; i < (n>>2); i++) {
00097         i1 = 2*i;
00098         i2 = n-i1;
00099         /* Separate even and odd FFTs */
00100         ev.re =  k1*(data[i1  ]+data[i2  ]);
00101         od.im = -k2*(data[i1  ]-data[i2  ]);
00102         ev.im =  k1*(data[i1+1]-data[i2+1]);
00103         od.re =  k2*(data[i1+1]+data[i2+1]);
00104         /* Apply twiddle factors to the odd FFT and add to the even FFT */
00105         data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
00106         data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
00107         data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
00108         data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
00109     }
00110     data[2*i+1]=s->sign_convention*data[2*i+1];
00111     if (s->inverse) {
00112         data[0] *= k1;
00113         data[1] *= k1;
00114         ff_fft_permute(&s->fft, (FFTComplex*)data);
00115         ff_fft_calc(&s->fft, (FFTComplex*)data);
00116     }
00117 }
00118 
00119 void ff_rdft_calc(RDFTContext *s, FFTSample *data)
00120 {
00121     ff_rdft_calc_c(s, data);
00122 }
00123 
00124 av_cold void ff_rdft_end(RDFTContext *s)
00125 {
00126     ff_fft_end(&s->fft);
00127 }

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