Line data    Source code

       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 Libav.
       6             :  *
       7             :  * Libav 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             :  * Libav 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 Libav; 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 "rdft.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
      33             : SINTABLE(16);
      34             : SINTABLE(32);
      35             : SINTABLE(64);
      36             : SINTABLE(128);
      37             : SINTABLE(256);
      38             : SINTABLE(512);
      39             : SINTABLE(1024);
      40             : SINTABLE(2048);
      41             : SINTABLE(4096);
      42             : SINTABLE(8192);
      43             : SINTABLE(16384);
      44             : SINTABLE(32768);
      45             : SINTABLE(65536);
      46             : #endif
      47             : static SINTABLE_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             :  */
      57           0 : static void rdft_calc_c(RDFTContext *s, FFTSample *data)
      58             : {
      59             :     int i, i1, i2;
      60             :     FFTComplex ev, od;
      61           0 :     const int n = 1 << s->nbits;
      62           0 :     const float k1 = 0.5;
      63           0 :     const float k2 = 0.5 - s->inverse;
      64           0 :     const FFTSample *tcos = s->tcos;
      65           0 :     const FFTSample *tsin = s->tsin;
      66             : 
      67           0 :     if (!s->inverse) {
      68           0 :         s->fft.fft_permute(&s->fft, (FFTComplex*)data);
      69           0 :         s->fft.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           0 :     ev.re = data[0];
      74           0 :     data[0] = ev.re+data[1];
      75           0 :     data[1] = ev.re-data[1];
      76           0 :     for (i = 1; i < (n>>2); i++) {
      77           0 :         i1 = 2*i;
      78           0 :         i2 = n-i1;
      79             :         /* Separate even and odd FFTs */
      80           0 :         ev.re =  k1*(data[i1  ]+data[i2  ]);
      81           0 :         od.im = -k2*(data[i1  ]-data[i2  ]);
      82           0 :         ev.im =  k1*(data[i1+1]-data[i2+1]);
      83           0 :         od.re =  k2*(data[i1+1]+data[i2+1]);
      84             :         /* Apply twiddle factors to the odd FFT and add to the even FFT */
      85           0 :         data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
      86           0 :         data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
      87           0 :         data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
      88           0 :         data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
      89             :     }
      90           0 :     data[2*i+1]=s->sign_convention*data[2*i+1];
      91           0 :     if (s->inverse) {
      92           0 :         data[0] *= k1;
      93           0 :         data[1] *= k1;
      94           0 :         s->fft.fft_permute(&s->fft, (FFTComplex*)data);
      95           0 :         s->fft.fft_calc(&s->fft, (FFTComplex*)data);
      96             :     }
      97           0 : }
      98             : 
      99           0 : av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
     100             : {
     101           0 :     int n = 1 << nbits;
     102             :     int i;
     103           0 :     const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n;
     104             : 
     105           0 :     s->nbits           = nbits;
     106           0 :     s->inverse         = trans == IDFT_C2R || trans == DFT_C2R;
     107           0 :     s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
     108             : 
     109           0 :     if (nbits < 4 || nbits > 16)
     110           0 :         return -1;
     111             : 
     112           0 :     if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 0)
     113           0 :         return -1;
     114             : 
     115           0 :     ff_init_ff_cos_tabs(nbits);
     116           0 :     s->tcos = ff_cos_tabs[nbits];
     117           0 :     s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2);
     118             : #if !CONFIG_HARDCODED_TABLES
     119           0 :     for (i = 0; i < (n>>2); i++) {
     120           0 :         s->tsin[i] = sin(i*theta);
     121             :     }
     122             : #endif
     123           0 :     s->rdft_calc   = rdft_calc_c;
     124             : 
     125             :     if (ARCH_ARM) ff_rdft_init_arm(s);
     126             : 
     127           0 :     return 0;
     128             : }
     129             : 
     130           0 : av_cold void ff_rdft_end(RDFTContext *s)
     131             : {
     132           0 :     ff_fft_end(&s->fft);
     133           0 : }