/*
  * (I)RDFT transforms
  * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */

 #include <stdlib.h>

 #include <math.h>

 #include "libavutil/mathematics.h"

 #include "rdft.h"

 
 /**

  * @file

  * (Inverse) Real Discrete Fourier Transforms.
  */
 
 /* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */

 #if !CONFIG_HARDCODED_TABLES

 SINTABLE(16);
 SINTABLE(32);
 SINTABLE(64);
 SINTABLE(128);
 SINTABLE(256);
 SINTABLE(512);
 SINTABLE(1024);
 SINTABLE(2048);
 SINTABLE(4096);
 SINTABLE(8192);
 SINTABLE(16384);
 SINTABLE(32768);
 SINTABLE(65536);

 #endif

 static SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {

     NULL, NULL, NULL, NULL,

     ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024,
     ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,
 };
 
 /** Map one real FFT into two parallel real even and odd FFTs. Then interleave
  * the two real FFTs into one complex FFT. Unmangle the results.
  * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
  */

 static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)

 {
     int i, i1, i2;
     FFTComplex ev, od;
     const int n = 1 << s->nbits;
     const float k1 = 0.5;
     const float k2 = 0.5 - s->inverse;
     const FFTSample *tcos = s->tcos;
     const FFTSample *tsin = s->tsin;
 
     if (!s->inverse) {

         s->fft.fft_permute(&s->fft, (FFTComplex*)data);
         s->fft.fft_calc(&s->fft, (FFTComplex*)data);

     }
     /* i=0 is a special case because of packing, the DC term is real, so we
        are going to throw the N/2 term (also real) in with it. */
     ev.re = data[0];
     data[0] = ev.re+data[1];
     data[1] = ev.re-data[1];
     for (i = 1; i < (n>>2); i++) {
         i1 = 2*i;
         i2 = n-i1;
         /* Separate even and odd FFTs */
         ev.re =  k1*(data[i1  ]+data[i2  ]);
         od.im = -k2*(data[i1  ]-data[i2  ]);
         ev.im =  k1*(data[i1+1]-data[i2+1]);
         od.re =  k2*(data[i1+1]+data[i2+1]);
         /* Apply twiddle factors to the odd FFT and add to the even FFT */
         data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
         data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
         data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
         data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
     }
     data[2*i+1]=s->sign_convention*data[2*i+1];
     if (s->inverse) {
         data[0] *= k1;
         data[1] *= k1;

         s->fft.fft_permute(&s->fft, (FFTComplex*)data);
         s->fft.fft_calc(&s->fft, (FFTComplex*)data);

     }
 }
 

 av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
 {
     int n = 1 << nbits;
     int i;
     const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n;
 
     s->nbits           = nbits;
     s->inverse         = trans == IDFT_C2R || trans == DFT_C2R;
     s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
 
     if (nbits < 4 || nbits > 16)
         return -1;
 
     if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 0)
         return -1;
 
     ff_init_ff_cos_tabs(nbits);
     s->tcos = ff_cos_tabs[nbits];
     s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2);
 #if !CONFIG_HARDCODED_TABLES
     for (i = 0; i < (n>>2); i++) {
         s->tsin[i] = sin(i*theta);
     }
 #endif
     s->rdft_calc   = ff_rdft_calc_c;

 
     if (ARCH_ARM) ff_rdft_init_arm(s);
 

     return 0;
 }
 

 av_cold void ff_rdft_end(RDFTContext *s)
 {
     ff_fft_end(&s->fft);
 }