/* fft/hc_init.c

 * 

 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007, 2009 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.

 */

TYPE(gsl_fft_halfcomplex_wavetable) *

FUNCTION(gsl_fft_halfcomplex_wavetable,alloc) (size_t n)

{

  int status;

  size_t i;

  size_t n_factors;

  size_t t, product, product_1, q;

  double d_theta;

  TYPE(gsl_fft_halfcomplex_wavetable) * wavetable ;

  if (n == 0)

    {

      GSL_ERROR_VAL ("length n must be positive integer", GSL_EDOM, 0);

    }

  wavetable = (TYPE(gsl_fft_halfcomplex_wavetable) *) 

    malloc(sizeof(TYPE(gsl_fft_halfcomplex_wavetable)));

  if (wavetable == NULL)

    {

      GSL_ERROR_VAL ("failed to allocate struct", GSL_ENOMEM, 0);

    }

  wavetable->trig = (TYPE(gsl_complex) *) malloc (n * sizeof (TYPE(gsl_complex)));

  if (wavetable->trig == NULL)

    {

      /* error in constructor, prevent memory leak */

      free(wavetable) ; 

      GSL_ERROR_VAL ("failed to allocate trigonometric lookup table", 

                        GSL_ENOMEM, 0);

    }

  wavetable->n = n ;

  status = fft_halfcomplex_factorize (n, &n_factors, wavetable->factor);

  if (status)

    {

      /* error in constructor, prevent memory leak */

      free(wavetable->trig) ; 

      free(wavetable) ; 

      GSL_ERROR_VAL ("factorization failed", GSL_EFACTOR, 0);

    }

  wavetable->nf = n_factors;

  d_theta = 2.0 * M_PI / ((double) n);

  t = 0;

  product = 1;

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

    {

      size_t j;

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

      wavetable->twiddle[i] = wavetable->trig + t;

      product_1 = product;      /* product_1 = p_(i-1) */

      product *= factor;

      q = n / product;

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

        {

          size_t k;

          size_t m = 0;

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

            {

              double theta;

              m = m + j * product_1;

              m = m % n;

              theta = d_theta * m;      /*  d_theta*j*k*product_1 */

              GSL_REAL(wavetable->trig[t]) = cos (theta);

              GSL_IMAG(wavetable->trig[t]) = sin (theta);

              t++;

            }

        }

    }

  if (t > (n / 2))

    {

      /* error in constructor, prevent memory leak */

      free(wavetable->trig) ; 

      free(wavetable) ; 

      GSL_ERROR_VAL ("overflowed trigonometric lookup table", GSL_ESANITY, 0);

    }

  return wavetable;

}

void

FUNCTION(gsl_fft_halfcomplex_wavetable,free) (TYPE(gsl_fft_halfcomplex_wavetable) * wavetable)

{

  RETURN_IF_NULL (wavetable);

  /* release trigonometric lookup tables */

  free (wavetable->trig);

  wavetable->trig = NULL;

  free (wavetable);

}