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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 <stdlib.h>
00022 #include <math.h>
00023 #include "libavutil/mathematics.h"
00024 #include "fft.h"
00025 
00031 /* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
00032 #if !CONFIG_HARDCODED_TABLES
00033 SINTABLE(16);
00034 SINTABLE(32);
00035 SINTABLE(64);
00036 SINTABLE(128);
00037 SINTABLE(256);
00038 SINTABLE(512);
00039 SINTABLE(1024);
00040 SINTABLE(2048);
00041 SINTABLE(4096);
00042 SINTABLE(8192);
00043 SINTABLE(16384);
00044 SINTABLE(32768);
00045 SINTABLE(65536);
00046 #endif
00047 SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {
00048     NULL, NULL, NULL, NULL,
00049     ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024,
00050     ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,
00051 };
00052 
00057 static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
00058 {
00059     int i, i1, i2;
00060     FFTComplex ev, od;
00061     const int n = 1 << s->nbits;
00062     const float k1 = 0.5;
00063     const float k2 = 0.5 - s->inverse;
00064     const FFTSample *tcos = s->tcos;
00065     const FFTSample *tsin = s->tsin;
00066 
00067     if (!s->inverse) {
00068         ff_fft_permute(&s->fft, (FFTComplex*)data);
00069         ff_fft_calc(&s->fft, (FFTComplex*)data);
00070     }
00071     /* i=0 is a special case because of packing, the DC term is real, so we
00072        are going to throw the N/2 term (also real) in with it. */
00073     ev.re = data[0];
00074     data[0] = ev.re+data[1];
00075     data[1] = ev.re-data[1];
00076     for (i = 1; i < (n>>2); i++) {
00077         i1 = 2*i;
00078         i2 = n-i1;
00079         /* Separate even and odd FFTs */
00080         ev.re =  k1*(data[i1  ]+data[i2  ]);
00081         od.im = -k2*(data[i1  ]-data[i2  ]);
00082         ev.im =  k1*(data[i1+1]-data[i2+1]);
00083         od.re =  k2*(data[i1+1]+data[i2+1]);
00084         /* Apply twiddle factors to the odd FFT and add to the even FFT */
00085         data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
00086         data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
00087         data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
00088         data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
00089     }
00090     data[2*i+1]=s->sign_convention*data[2*i+1];
00091     if (s->inverse) {
00092         data[0] *= k1;
00093         data[1] *= k1;
00094         ff_fft_permute(&s->fft, (FFTComplex*)data);
00095         ff_fft_calc(&s->fft, (FFTComplex*)data);
00096     }
00097 }
00098 
00099 av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
00100 {
00101     int n = 1 << nbits;
00102     int i;
00103     const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n;
00104 
00105     s->nbits           = nbits;
00106     s->inverse         = trans == IDFT_C2R || trans == DFT_C2R;
00107     s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
00108 
00109     if (nbits < 4 || nbits > 16)
00110         return -1;
00111 
00112     if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 0)
00113         return -1;
00114 
00115     ff_init_ff_cos_tabs(nbits);
00116     s->tcos = ff_cos_tabs[nbits];
00117     s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2);
00118 #if !CONFIG_HARDCODED_TABLES
00119     for (i = 0; i < (n>>2); i++) {
00120         s->tsin[i] = sin(i*theta);
00121     }
00122 #endif
00123     s->rdft_calc   = ff_rdft_calc_c;
00124 
00125     if (ARCH_ARM) ff_rdft_init_arm(s);
00126 
00127     return 0;
00128 }
00129 
00130 av_cold void ff_rdft_end(RDFTContext *s)
00131 {
00132     ff_fft_end(&s->fft);
00133 }

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