/* fft/c_pass_n.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.

 */

static int

FUNCTION(fft_complex,pass_n) (BASE in[],

                              const size_t istride,

                              BASE out[],

                              const size_t ostride,

                              const gsl_fft_direction sign,

                              const size_t factor,

                              const size_t product,

                              const size_t n,

                              const TYPE(gsl_complex) twiddle[])

{

  size_t i = 0, j = 0;

  size_t k, k1;

  const size_t m = n / factor;

  const size_t q = n / product;

  const size_t p_1 = product / factor;

  const size_t jump = (factor - 1) * p_1;

  size_t e, e1;

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

    {

      REAL(out,ostride,i) = REAL(in,istride,i);

      IMAG(out,ostride,i) = IMAG(in,istride,i);

    }

  for (e = 1; e < (factor - 1) / 2 + 1; e++)

    {

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

        {

          const size_t idx = i + e * m;

          const size_t idxc = i + (factor - e) * m;

          REAL(out,ostride,idx) = REAL(in,istride,idx) + REAL(in,istride,idxc);

          IMAG(out,ostride,idx) = IMAG(in,istride,idx) + IMAG(in,istride,idxc);

          REAL(out,ostride,idxc) = REAL(in,istride,idx) - REAL(in,istride,idxc);

          IMAG(out,ostride,idxc) = IMAG(in,istride,idx) - IMAG(in,istride,idxc);

        }

    }

  /* e = 0 */

  for (i=0 ; i

    {

      REAL(in,istride,i) = REAL(out,ostride,i);

      IMAG(in,istride,i) = IMAG(out,ostride,i);

    }

  for (e1 = 1; e1 < (factor - 1) / 2 + 1; e1++)

    {

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

        {

          REAL(in,istride,i) += REAL(out,ostride,i + e1*m) ;

          IMAG(in,istride,i) += IMAG(out,ostride,i + e1*m) ;

        }

    }

  for (e = 1; e < (factor-1)/2 + 1; e++)

    {

      size_t idx = e*q ;

      const size_t idx_step = e * q ;

      ATOMIC w_real, w_imag ;

      const size_t em = e * m ;

      const size_t ecm = (factor - e) * m ;

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

        {

          REAL(in,istride,i+em) = REAL(out,ostride,i) ;

          IMAG(in,istride,i+em) = IMAG(out,ostride,i) ;

          REAL(in,istride,i+ecm) = REAL(out,ostride,i) ;

          IMAG(in,istride,i+ecm) = IMAG(out,ostride,i) ;

        }

      for (e1 = 1; e1 < (factor - 1) / 2 + 1; e1++)

        {

          if (idx == 0) {

            w_real = 1 ;

            w_imag = 0 ;

          } else {

            if (sign == gsl_fft_forward) {

              w_real = GSL_REAL(twiddle[idx - 1]) ;

              w_imag = GSL_IMAG(twiddle[idx - 1]) ;

            } else {

              w_real = GSL_REAL(twiddle[idx - 1]) ;

              w_imag = -GSL_IMAG(twiddle[idx - 1]) ;

            }

          }

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

            {

              const ATOMIC xp_real = REAL(out,ostride,i + e1 * m);

              const ATOMIC xp_imag = IMAG(out,ostride,i + e1 * m);

              const ATOMIC xm_real = REAL(out,ostride,i + (factor - e1) *m);

              const ATOMIC xm_imag = IMAG(out,ostride,i + (factor - e1) *m);

              const ATOMIC ap = w_real * xp_real ;

              const ATOMIC am = w_imag * xm_imag ; 

              ATOMIC sum_real = ap - am;

              ATOMIC sumc_real = ap + am;

              const ATOMIC bp = w_real * xp_imag ;

              const ATOMIC bm = w_imag * xm_real ;

              ATOMIC sum_imag = bp + bm;

              ATOMIC sumc_imag = bp - bm;

              REAL(in,istride,i + em) += sum_real;

              IMAG(in,istride,i + em) += sum_imag;

              REAL(in,istride,i + ecm) += sumc_real;

              IMAG(in,istride,i + ecm) += sumc_imag;

            }

          idx += idx_step ;

          idx %= factor * q ;

        }

    }

  i = 0;

  j = 0;

  /* k = 0 */

  for (k1 = 0; k1 < p_1; k1++)

    {

      REAL(out,ostride,k1) = REAL(in,istride,k1);

      IMAG(out,ostride,k1) = IMAG(in,istride,k1);

    }

  for (e1 = 1; e1 < factor; e1++)

    {

      for (k1 = 0; k1 < p_1; k1++)

        {

          REAL(out,ostride,k1 + e1 * p_1) = REAL(in,istride,k1 + e1 * m) ;

          IMAG(out,ostride,k1 + e1 * p_1) = IMAG(in,istride,k1 + e1 * m) ;

        }

    }

  i = p_1 ;

  j = product ;

  for (k = 1; k < q; k++)

    {

      for (k1 = 0; k1 < p_1; k1++)

        {

          REAL(out,ostride,j) = REAL(in,istride,i);

          IMAG(out,ostride,j) = IMAG(in,istride,i);

          i++;

          j++;

        }

      j += jump;

    }

  i = p_1 ;

  j = product ;

  for (k = 1; k < q; k++)

    {

      for (k1 = 0; k1 < p_1; k1++)

        {

          for (e1 = 1; e1 < factor; e1++)

            {

              ATOMIC x_real = REAL(in, istride,i + e1 * m);

              ATOMIC x_imag = IMAG(in, istride,i + e1 * m);

              ATOMIC w_real, w_imag ;

              if (sign == gsl_fft_forward) {

                w_real = GSL_REAL(twiddle[(e1-1)*q + k-1]) ;

                w_imag = GSL_IMAG(twiddle[(e1-1)*q + k-1]) ;

              } else {

                w_real = GSL_REAL(twiddle[(e1-1)*q + k-1]) ;

                w_imag = -GSL_IMAG(twiddle[(e1-1)*q + k-1]) ; 

              }

              REAL(out,ostride,j + e1 * p_1) = w_real * x_real - w_imag * x_imag;

              IMAG(out,ostride,j + e1 * p_1) = w_real * x_imag + w_imag * x_real;

            }

          i++;

          j++;

        }

      j += jump;

    }

  return 0;

}