/* fft/hc_main.c
 * 
 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Brian Gough
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or (at
 * your option) any later version.
 * 
 * This program 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
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include "gsl__config.h"
#include <stdlib.h>
#include <math.h>

#include "gsl_errno.h"
#include "gsl_complex.h"
#include "gsl_fft_halfcomplex.h"

#include "gsl_fft__hc_pass.h"

int
FUNCTION(gsl_fft_halfcomplex,backward) (BASE data[], const size_t stride, 
                                        const size_t n,
                                        const TYPE(gsl_fft_halfcomplex_wavetable) * wavetable,
                                        TYPE(gsl_fft_real_workspace) * work)
{
  int status = FUNCTION(gsl_fft_halfcomplex,transform) (data, stride, n, wavetable, work) ;
  return status ;
}

int
FUNCTION(gsl_fft_halfcomplex,inverse) (BASE data[], const size_t stride, 
                                       const size_t n,
                                       const TYPE(gsl_fft_halfcomplex_wavetable) * wavetable,
                                       TYPE(gsl_fft_real_workspace) * work)
{
  int status = FUNCTION(gsl_fft_halfcomplex,transform) (data, stride, n, wavetable, work);

  if (status)
    {
      return status;
    }

  /* normalize inverse fft with 1/n */

  {
    const double norm = 1.0 / n;
    size_t i;
    for (i = 0; i < n; i++)
      {
        data[stride*i] *= norm;
      }
  }
  return status;
}

int
FUNCTION(gsl_fft_halfcomplex,transform) (BASE data[], const size_t stride, const size_t n,
                                         const TYPE(gsl_fft_halfcomplex_wavetable) * wavetable,
                                         TYPE(gsl_fft_real_workspace) * work)
{
  BASE * const scratch = work->scratch;

  BASE * in;
  BASE * out;
  size_t istride, ostride ;


  size_t factor, product, q;
  size_t i;
  size_t nf;
  int state;
  int product_1;
  int tskip;
  TYPE(gsl_complex) *twiddle1, *twiddle2, *twiddle3, *twiddle4;

  if (n == 0)
    {
      GSL_ERROR ("length n must be positive integer", GSL_EDOM);
    }

  if (n == 1)
    {                           /* FFT of one data point is the identity */
      return 0;
    }

  if (n != wavetable->n)
    {
      GSL_ERROR ("wavetable does not match length of data", GSL_EINVAL);
    }

  if (n != work->n)
    {
      GSL_ERROR ("workspace does not match length of data", GSL_EINVAL);
    }

  nf = wavetable->nf;
  product = 1;
  state = 0;

  for (i = 0; i < nf; i++)
    {
      factor = wavetable->factor[i];
      product_1 = product;
      product *= factor;
      q = n / product;

      tskip = (q + 1) / 2 - 1;

      if (state == 0)
        {
          in = data;
          istride = stride;
          out = scratch;
          ostride = 1;
          state = 1;
        }
      else
        {
          in = scratch;
          istride = 1;
          out = data;
          ostride = stride;
          state = 0;
        }

      if (factor == 2)
        {
          twiddle1 = wavetable->twiddle[i];
          FUNCTION(fft_halfcomplex,pass_2) (in, istride, out, ostride, 
                                            product, n, twiddle1);
        }
      else if (factor == 3)
        {
          twiddle1 = wavetable->twiddle[i];
          twiddle2 = twiddle1 + tskip;
          FUNCTION(fft_halfcomplex,pass_3) (in, istride, out, ostride,
                                            product, n, twiddle1, twiddle2);
        }
      else if (factor == 4)
        {
          twiddle1 = wavetable->twiddle[i];
          twiddle2 = twiddle1 + tskip;
          twiddle3 = twiddle2 + tskip;
          FUNCTION(fft_halfcomplex,pass_4) (in, istride, out, ostride,
                                            product, n, twiddle1, twiddle2, 
                                            twiddle3);
        }
      else if (factor == 5)
        {
          twiddle1 = wavetable->twiddle[i];
          twiddle2 = twiddle1 + tskip;
          twiddle3 = twiddle2 + tskip;
          twiddle4 = twiddle3 + tskip;
          FUNCTION(fft_halfcomplex,pass_5) (in, istride, out, ostride,
                                            product, n, twiddle1, twiddle2, 
                                            twiddle3, twiddle4);
        }
      else
        {
          twiddle1 = wavetable->twiddle[i];
          FUNCTION(fft_halfcomplex,pass_n) (in, istride, out, ostride,
                                            factor, product, n, twiddle1);
        }
    }

  if (state == 1)               /* copy results back from scratch to data */
    {
      for (i = 0; i < n; i++)
        {
          data[stride*i] = scratch[i] ;
        }
    }

  return 0;

}


