/* fft/hc_pass_2.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 void

FUNCTION(fft_halfcomplex,pass_2) (const BASE in[],

                                  const size_t istride,

                                  BASE out[],

                                  const size_t ostride,

                                  const size_t product,

                                  const size_t n,

                                  const TYPE(gsl_complex) twiddle[])

{

  size_t i, j, k, k1, jump;

  size_t factor, q, m, product_1;

  i = 0;

  j = 0;

  factor = 2;

  m = n / factor;

  q = n / product;

  product_1 = product / factor;

  jump = (factor - 1) * q;

  for (k1 = 0; k1 < product_1; k1++)

    {

      const ATOMIC r0 = VECTOR(in,istride,2 * k1 * q);

      const ATOMIC r1 = VECTOR(in,istride,2 * k1 * q + 2 * q - 1);

      const ATOMIC s0 = r0 + r1;

      const ATOMIC s1 = r0 - r1;

      VECTOR(out,ostride,q * k1) = s0;

      VECTOR(out,ostride,q * k1 + m) = s1;

    }

  if (q == 1)

    return;

  for (k = 1; k < (q + 1) / 2; k++)

    {

      const ATOMIC w_real = GSL_REAL(twiddle[k - 1]);

      const ATOMIC w_imag = GSL_IMAG(twiddle[k - 1]);

      for (k1 = 0; k1 < product_1; k1++)

        {

          const size_t from0 = 2 * k1 * q + 2 * k - 1;

          const size_t from1 = 2 * k1 * q - 2 * k + 2 * q - 1;

          const ATOMIC z0_real = VECTOR(in,istride,from0);

          const ATOMIC z0_imag = VECTOR(in,istride,from0 + 1);

          const ATOMIC z1_real = VECTOR(in,istride,from1);

          const ATOMIC z1_imag = VECTOR(in,istride,from1 + 1);

          /* compute x = W(2) z */

          /* x0 = z0 + z1 */

          const ATOMIC x0_real = z0_real + z1_real;

          const ATOMIC x0_imag = z0_imag - z1_imag;

          /* x1 = z0 - z1 */

          const ATOMIC x1_real = z0_real - z1_real;

          const ATOMIC x1_imag = z0_imag + z1_imag;

          const size_t to0 = k1 * q + 2 * k - 1;

          const size_t to1 = to0 + m;

          VECTOR(out,ostride,to0) = x0_real;

          VECTOR(out,ostride,to0 + 1) = x0_imag;

          VECTOR(out,ostride,to1) = w_real * x1_real - w_imag * x1_imag;

          VECTOR(out,ostride,to1 + 1) = w_imag * x1_real + w_real * x1_imag;

        }

    }

  if (q % 2 == 1)

    return;

  for (k1 = 0; k1 < product_1; k1++)

    {

      const size_t from0 = 2 * k1 * q + q - 1;

      const size_t to0 = k1 * q + q - 1;

      const size_t to1 = to0 + m;

      VECTOR(out,ostride,to0) = 2 * VECTOR(in,istride,from0);

      VECTOR(out,ostride,to1) = -2 * VECTOR(in,istride,from0 + 1);

    }

  return;

}