/* fft/real_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 <config.h>

#include <stdlib.h>

#include <math.h>

#include <gsl/gsl_errno.h>

#include <gsl/gsl_complex.h>

#include <gsl/gsl_fft_real.h>

#include "real_pass.h"

int

FUNCTION(gsl_fft_real,transform) (BASE data[], const size_t stride, const size_t n,

                                  const TYPE(gsl_fft_real_wavetable) * wavetable,

                                  TYPE(gsl_fft_real_workspace) * work)

{

  const size_t nf = wavetable->nf;

  size_t i;

  size_t q, product = 1;

  size_t tskip;

  size_t product_1;

  BASE *const scratch = work->scratch;

  TYPE(gsl_complex) *twiddle1, *twiddle2, *twiddle3, *twiddle4;

  size_t state = 0;

  BASE *in = data;

  size_t istride = stride ;

  BASE *out = scratch;

  size_t ostride = 1 ;

  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);

    }

  for (i = 0; i < nf; i++)

    {

      const size_t factor = wavetable->factor[i];

      product_1 = product;

      product *= factor;

      q = n / product;

      tskip = (product_1 + 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_real,pass_2) (in, istride, out, ostride, product, n, twiddle1);

        }

      else if (factor == 3)

        {

          twiddle1 = wavetable->twiddle[i];

          twiddle2 = twiddle1 + tskip;

          FUNCTION(fft_real,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_real,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_real,pass_5) (in, istride, out, ostride, product, n, twiddle1,

                                     twiddle2, twiddle3, twiddle4);

        }

      else

        {

          twiddle1 = wavetable->twiddle[i];

          FUNCTION(fft_real,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;

}