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/* fft/hc_pass_2.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 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;
}
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