/* fft/hc_init.c
 * 
 * Copyright (C) 1996, 1997, 1998, 1999, 2000 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 2 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., 675 Mass Ave, Cambridge, MA 02139, 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)
{

  /* release trigonometric lookup tables */

  free (wavetable->trig);
  wavetable->trig = NULL;

  free (wavetable);
}

