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/* fft/c_pass_4.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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
static int
FUNCTION(fft_complex,pass_4) (const BASE in[],
const size_t istride,
BASE out[],
const size_t ostride,
const gsl_fft_direction sign,
const size_t product,
const size_t n,
const TYPE(gsl_complex) twiddle1[],
const TYPE(gsl_complex) twiddle2[],
const TYPE(gsl_complex) twiddle3[])
{
size_t i = 0, j = 0;
size_t k, k1;
const size_t factor = 4;
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;
for (k = 0; k < q; k++)
{
ATOMIC w1_real, w1_imag, w2_real, w2_imag, w3_real, w3_imag;
if (k == 0)
{
w1_real = 1.0;
w1_imag = 0.0;
w2_real = 1.0;
w2_imag = 0.0;
w3_real = 1.0;
w3_imag = 0.0;
}
else
{
if (sign == gsl_fft_forward)
{
/* forward tranform */
w1_real = GSL_REAL(twiddle1[k - 1]);
w1_imag = GSL_IMAG(twiddle1[k - 1]);
w2_real = GSL_REAL(twiddle2[k - 1]);
w2_imag = GSL_IMAG(twiddle2[k - 1]);
w3_real = GSL_REAL(twiddle3[k - 1]);
w3_imag = GSL_IMAG(twiddle3[k - 1]);
}
else
{
/* backward tranform: w -> conjugate(w) */
w1_real = GSL_REAL(twiddle1[k - 1]);
w1_imag = -GSL_IMAG(twiddle1[k - 1]);
w2_real = GSL_REAL(twiddle2[k - 1]);
w2_imag = -GSL_IMAG(twiddle2[k - 1]);
w3_real = GSL_REAL(twiddle3[k - 1]);
w3_imag = -GSL_IMAG(twiddle3[k - 1]);
}
}
for (k1 = 0; k1 < p_1; k1++)
{
const ATOMIC z0_real = REAL(in,istride,i);
const ATOMIC z0_imag = IMAG(in,istride,i);
const ATOMIC z1_real = REAL(in,istride,i+m);
const ATOMIC z1_imag = IMAG(in,istride,i+m);
const ATOMIC z2_real = REAL(in,istride,i+2*m);
const ATOMIC z2_imag = IMAG(in,istride,i+2*m);
const ATOMIC z3_real = REAL(in,istride,i+3*m);
const ATOMIC z3_imag = IMAG(in,istride,i+3*m);
/* compute x = W(4) z */
/* t1 = z0 + z2 */
const ATOMIC t1_real = z0_real + z2_real;
const ATOMIC t1_imag = z0_imag + z2_imag;
/* t2 = z1 + z3 */
const ATOMIC t2_real = z1_real + z3_real;
const ATOMIC t2_imag = z1_imag + z3_imag;
/* t3 = z0 - z2 */
const ATOMIC t3_real = z0_real - z2_real;
const ATOMIC t3_imag = z0_imag - z2_imag;
/* t4 = (+/-) (z1 - z3) */
const ATOMIC t4_real = ((int) sign) * (z1_real - z3_real);
const ATOMIC t4_imag = ((int) sign) * (z1_imag - z3_imag);
/* x0 = t1 + t2 */
const ATOMIC x0_real = t1_real + t2_real;
const ATOMIC x0_imag = t1_imag + t2_imag;
/* x1 = t3 + i t4 */
const ATOMIC x1_real = t3_real - t4_imag;
const ATOMIC x1_imag = t3_imag + t4_real;
/* x2 = t1 - t2 */
const ATOMIC x2_real = t1_real - t2_real;
const ATOMIC x2_imag = t1_imag - t2_imag;
/* x3 = t3 - i t4 */
const ATOMIC x3_real = t3_real + t4_imag;
const ATOMIC x3_imag = t3_imag - t4_real;
/* apply twiddle factors */
/* to0 = 1 * x0 */
REAL(out,ostride,j) = x0_real;
IMAG(out,ostride,j) = x0_imag;
/* to1 = w1 * x1 */
REAL(out, ostride, j + p_1) = w1_real * x1_real - w1_imag * x1_imag;
IMAG(out, ostride, j + p_1) = w1_real * x1_imag + w1_imag * x1_real;
/* to2 = w2 * x2 */
REAL(out, ostride, j + 2 * p_1) = w2_real * x2_real - w2_imag * x2_imag;
IMAG(out, ostride, j + 2 * p_1) = w2_real * x2_imag + w2_imag * x2_real;
/* to3 = w3 * x3 */
REAL(out, ostride, j + 3 * p_1) = w3_real * x3_real - w3_imag * x3_imag;
IMAG(out, ostride, j + 3 * p_1) = w3_real * x3_imag + w3_imag * x3_real;
i++;
j++;
}
j += jump;
}
return 0;
}
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