#include "hc_pass.h"

void
FUNCTION(fft_halfcomplex,pass_4) (const BASE in[],
				  const size_t istride,
				  BASE out[],
				  const size_t ostride,
				  const size_t product,
				  const size_t n,
				  const gsl_complex twiddle1[],
				  const gsl_complex twiddle2[],
				  const gsl_complex twiddle3[])
{
  size_t i, j, k, k1, jump;
  size_t factor, q, m, product_1;

  i = 0;
  j = 0;

  factor = 4;
  m = n / factor;
  q = n / product;
  product_1 = product / factor;
  jump = (factor - 1) * q;

  for (k1 = 0; k1 < product_1; k1++)
    {
      const size_t from0 = 4 * k1 * q;
      const size_t from1 = from0 + 2 * q - 1;
      const size_t from2 = from1 + 2 * q;

      const double z0_real = VECTOR(in,istride,from0);
      const double z1_real = VECTOR(in,istride,from1);
      const double z1_imag = VECTOR(in,istride,from1 + 1);
      const double z2_real = VECTOR(in,istride,from2);

      const double t1_real = z0_real + z2_real;
      const double t2_real = 2 * z1_real;
      const double t3_real = z0_real - z2_real;
      const double t4_imag = 2 * z1_imag;

      const size_t to0 = q * k1;
      const size_t to1 = to0 + m;
      const size_t to2 = to1 + m;
      const size_t to3 = to2 + m;

      VECTOR(out,ostride,to0) = t1_real + t2_real;
      VECTOR(out,ostride,to1) = t3_real - t4_imag;
      VECTOR(out,ostride,to2) = t1_real - t2_real;
      VECTOR(out,ostride,to3) = t3_real + t4_imag;
    }

  if (q == 1)
    return;

  for (k = 1; k < (q + 1) / 2; k++)
    {
      const double w1_real = GSL_REAL(twiddle1[k - 1]);
      const double w1_imag = GSL_IMAG(twiddle1[k - 1]);
      const double w2_real = GSL_REAL(twiddle2[k - 1]);
      const double w2_imag = GSL_IMAG(twiddle2[k - 1]);
      const double w3_real = GSL_REAL(twiddle3[k - 1]);
      const double w3_imag = GSL_IMAG(twiddle3[k - 1]);

      for (k1 = 0; k1 < product_1; k1++)
	{
	  const size_t from0 = 4 * k1 * q + 2 * k - 1;
	  const size_t from1 = from0 + 2 * q;
	  const size_t from2 = 4 * k1 * q - 2 * k + 2 * q - 1;
	  const size_t from3 = from2 + 2 * q;

	  const double z0_real = VECTOR(in,istride,from0);
	  const double z0_imag = VECTOR(in,istride,from0 + 1);

	  const double z1_real = VECTOR(in,istride,from1);
	  const double z1_imag = VECTOR(in,istride,from1 + 1);

	  const double z2_real = VECTOR(in,istride,from3);
	  const double z2_imag = -VECTOR(in,istride,from3 + 1);

	  const double z3_real = VECTOR(in,istride,from2);
	  const double z3_imag = -VECTOR(in,istride,from2 + 1);

	  /* compute x = W(4) z */

	  /* t1 = z0 + z2 */
	  const double t1_real = z0_real + z2_real;
	  const double t1_imag = z0_imag + z2_imag;

	  /* t2 = z1 + z3 */
	  const double t2_real = z1_real + z3_real;
	  const double t2_imag = z1_imag + z3_imag;

	  /* t3 = z0 - z2 */
	  const double t3_real = z0_real - z2_real;
	  const double t3_imag = z0_imag - z2_imag;

	  /* t4 = (z1 - z3) */
	  const double t4_real = (z1_real - z3_real);
	  const double t4_imag = (z1_imag - z3_imag);

	  /* x0 = t1 + t2 */
	  const double x0_real = t1_real + t2_real;
	  const double x0_imag = t1_imag + t2_imag;

	  /* x1 = t3 + i t4 */
	  const double x1_real = t3_real - t4_imag;
	  const double x1_imag = t3_imag + t4_real;

	  /* x2 = t1 - t2 */
	  const double x2_real = t1_real - t2_real;
	  const double x2_imag = t1_imag - t2_imag;

	  /* x3 = t3 - i t4 */
	  const double x3_real = t3_real + t4_imag;
	  const double x3_imag = t3_imag - t4_real;

	  const size_t to0 = k1 * q + 2 * k - 1;
	  const size_t to1 = to0 + m;
	  const size_t to2 = to1 + m;
	  const size_t to3 = to2 + m;

	  VECTOR(out,ostride,to0) = x0_real;
	  VECTOR(out,ostride,to0 + 1) = x0_imag;

	  VECTOR(out,ostride,to1) = w1_real * x1_real - w1_imag * x1_imag;
	  VECTOR(out,ostride,to1 + 1) = w1_imag * x1_real + w1_real * x1_imag;

	  VECTOR(out,ostride,to2) = w2_real * x2_real - w2_imag * x2_imag;
	  VECTOR(out,ostride,to2 + 1) = w2_imag * x2_real + w2_real * x2_imag;

	  /* to3 = w3 * x3 */
	  VECTOR(out,ostride,to3) = w3_real * x3_real - w3_imag * x3_imag;
	  VECTOR(out,ostride,to3 + 1) = w3_real * x3_imag + w3_imag * x3_real;

	}
    }

  if (q % 2 == 1)
    return;

  for (k1 = 0; k1 < product_1; k1++)
    {
      const size_t from0 = 4 * k1 * q + q - 1;
      const size_t from1 = from0 + 2 * q;

      const double z0_real = VECTOR(in,istride,from0);
      const double z0_imag = VECTOR(in,istride,from0 + 1);

      const double z1_real = VECTOR(in,istride,from1);
      const double z1_imag = VECTOR(in,istride,from1 + 1);

      const double t1_real = sqrt (2.0) * (z0_imag + z1_imag);
      const double t2_real = sqrt (2.0) * (z0_real - z1_real);

      const double x0_real = 2 * (z0_real + z1_real);
      const double x1_real = t2_real - t1_real;
      const double x2_real = 2 * (z1_imag - z0_imag);
      const double x3_real = -(t2_real + t1_real);

      const size_t to0 = k1 * q + q - 1;
      const size_t to1 = to0 + m;
      const size_t to2 = to1 + m;
      const size_t to3 = to2 + m;

      VECTOR(out,ostride,to0) = x0_real;
      VECTOR(out,ostride,to1) = x1_real;
      VECTOR(out,ostride,to2) = x2_real;
      VECTOR(out,ostride,to3) = x3_real;
    }
  return;
}