| /* fft/c_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 int |
| FUNCTION(fft_complex,pass_2) (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) twiddle[]) |
| { |
| size_t i = 0, j = 0; |
| size_t k, k1; |
| |
| const size_t factor = 2; |
| const size_t m = n / factor; |
| const size_t q = n / product; |
| const size_t product_1 = product / factor; |
| const size_t jump = (factor - 1) * product_1; |
| |
| for (k = 0; k < q; k++) |
| { |
| ATOMIC w_real, w_imag; |
| |
| if (k == 0) |
| { |
| w_real = 1.0; |
| w_imag = 0.0; |
| } |
| else |
| { |
| if (sign == gsl_fft_forward) |
| { |
| /* forward tranform */ |
| w_real = GSL_REAL(twiddle[k - 1]); |
| w_imag = GSL_IMAG(twiddle[k - 1]); |
| } |
| else |
| { |
| /* backward tranform: w -> conjugate(w) */ |
| w_real = GSL_REAL(twiddle[k - 1]); |
| w_imag = -GSL_IMAG(twiddle[k - 1]); |
| } |
| } |
| |
| for (k1 = 0; k1 < product_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); |
| |
| /* 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; |
| |
| /* apply twiddle factors */ |
| |
| /* out0 = 1 * x0 */ |
| REAL(out,ostride,j) = x0_real; |
| IMAG(out,ostride,j) = x0_imag; |
| |
| /* out1 = w * x1 */ |
| REAL(out,ostride,j+product_1) = w_real * x1_real - w_imag * x1_imag; |
| IMAG(out,ostride,j+product_1) = w_real * x1_imag + w_imag * x1_real; |
| |
| i++; |
| j++; |
| } |
| j += jump; |
| } |
| return 0; |
| } |