3 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Brian Gough
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 3 of the License, or (at
8 * your option) any later version.
10 * This program is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
21 FUNCTION(fft_complex,pass_4) (const BASE in[],
25 const gsl_fft_direction sign,
28 const TYPE(gsl_complex) twiddle1[],
29 const TYPE(gsl_complex) twiddle2[],
30 const TYPE(gsl_complex) twiddle3[])
35 const size_t factor = 4;
36 const size_t m = n / factor;
37 const size_t q = n / product;
38 const size_t p_1 = product / factor;
39 const size_t jump = (factor - 1) * p_1;
41 for (k = 0; k < q; k++)
43 ATOMIC w1_real, w1_imag, w2_real, w2_imag, w3_real, w3_imag;
56 if (sign == gsl_fft_forward)
58 /* forward tranform */
59 w1_real = GSL_REAL(twiddle1[k - 1]);
60 w1_imag = GSL_IMAG(twiddle1[k - 1]);
61 w2_real = GSL_REAL(twiddle2[k - 1]);
62 w2_imag = GSL_IMAG(twiddle2[k - 1]);
63 w3_real = GSL_REAL(twiddle3[k - 1]);
64 w3_imag = GSL_IMAG(twiddle3[k - 1]);
68 /* backward tranform: w -> conjugate(w) */
69 w1_real = GSL_REAL(twiddle1[k - 1]);
70 w1_imag = -GSL_IMAG(twiddle1[k - 1]);
71 w2_real = GSL_REAL(twiddle2[k - 1]);
72 w2_imag = -GSL_IMAG(twiddle2[k - 1]);
73 w3_real = GSL_REAL(twiddle3[k - 1]);
74 w3_imag = -GSL_IMAG(twiddle3[k - 1]);
78 for (k1 = 0; k1 < p_1; k1++)
80 const ATOMIC z0_real = REAL(in,istride,i);
81 const ATOMIC z0_imag = IMAG(in,istride,i);
82 const ATOMIC z1_real = REAL(in,istride,i+m);
83 const ATOMIC z1_imag = IMAG(in,istride,i+m);
84 const ATOMIC z2_real = REAL(in,istride,i+2*m);
85 const ATOMIC z2_imag = IMAG(in,istride,i+2*m);
86 const ATOMIC z3_real = REAL(in,istride,i+3*m);
87 const ATOMIC z3_imag = IMAG(in,istride,i+3*m);
89 /* compute x = W(4) z */
92 const ATOMIC t1_real = z0_real + z2_real;
93 const ATOMIC t1_imag = z0_imag + z2_imag;
96 const ATOMIC t2_real = z1_real + z3_real;
97 const ATOMIC t2_imag = z1_imag + z3_imag;
100 const ATOMIC t3_real = z0_real - z2_real;
101 const ATOMIC t3_imag = z0_imag - z2_imag;
103 /* t4 = (+/-) (z1 - z3) */
104 const ATOMIC t4_real = ((int) sign) * (z1_real - z3_real);
105 const ATOMIC t4_imag = ((int) sign) * (z1_imag - z3_imag);
108 const ATOMIC x0_real = t1_real + t2_real;
109 const ATOMIC x0_imag = t1_imag + t2_imag;
112 const ATOMIC x1_real = t3_real - t4_imag;
113 const ATOMIC x1_imag = t3_imag + t4_real;
116 const ATOMIC x2_real = t1_real - t2_real;
117 const ATOMIC x2_imag = t1_imag - t2_imag;
120 const ATOMIC x3_real = t3_real + t4_imag;
121 const ATOMIC x3_imag = t3_imag - t4_real;
123 /* apply twiddle factors */
126 REAL(out,ostride,j) = x0_real;
127 IMAG(out,ostride,j) = x0_imag;
130 REAL(out, ostride, j + p_1) = w1_real * x1_real - w1_imag * x1_imag;
131 IMAG(out, ostride, j + p_1) = w1_real * x1_imag + w1_imag * x1_real;
134 REAL(out, ostride, j + 2 * p_1) = w2_real * x2_real - w2_imag * x2_imag;
135 IMAG(out, ostride, j + 2 * p_1) = w2_real * x2_imag + w2_imag * x2_real;
138 REAL(out, ostride, j + 3 * p_1) = w3_real * x3_real - w3_imag * x3_imag;
139 IMAG(out, ostride, j + 3 * p_1) = w3_real * x3_imag + w3_imag * x3_real;