| /* 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; |
| } |