diff options
Diffstat (limited to 'gsl-1.9/fft/real_pass_3.c')
| -rw-r--r-- | gsl-1.9/fft/real_pass_3.c | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/gsl-1.9/fft/real_pass_3.c b/gsl-1.9/fft/real_pass_3.c new file mode 100644 index 0000000..561a156 --- /dev/null +++ b/gsl-1.9/fft/real_pass_3.c @@ -0,0 +1,166 @@ +/* fft/real_pass_3.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_real,pass_3) (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) twiddle1[], + const TYPE(gsl_complex) twiddle2[]) +{ + size_t k, k1; + + const size_t factor = 3; + const size_t m = n / factor; + const size_t q = n / product; + const size_t product_1 = product / factor; + + const ATOMIC tau = sqrt (3.0) / 2.0; + + for (k1 = 0; k1 < q; k1++) + { + const size_t from0 = k1 * product_1; + const size_t from1 = from0 + m; + const size_t from2 = from1 + m; + + const ATOMIC z0_real = VECTOR(in,istride,from0); + const ATOMIC z1_real = VECTOR(in,istride,from1); + const ATOMIC z2_real = VECTOR(in,istride,from2); + + const ATOMIC t1 = z1_real + z2_real; + + const ATOMIC x0_real = z0_real + t1; + const ATOMIC x1_real = z0_real - t1 / 2.0; + const ATOMIC x1_imag = -tau * (z1_real - z2_real); + + const size_t to0 = product * k1; + const size_t to1 = to0 + 2 * product_1 - 1; + + VECTOR(out,ostride,to0) = x0_real; + VECTOR(out,ostride,to1) = x1_real; + VECTOR(out,ostride,to1 + 1) = x1_imag; + } + + if (product_1 == 1) + return; + + for (k = 1; k < (product_1 + 1) / 2; k++) + { + const ATOMIC w1_real = GSL_REAL(twiddle1[k - 1]); + const ATOMIC w1_imag = -GSL_IMAG(twiddle1[k - 1]); + const ATOMIC w2_real = GSL_REAL(twiddle2[k - 1]); + const ATOMIC w2_imag = -GSL_IMAG(twiddle2[k - 1]); + + for (k1 = 0; k1 < q; k1++) + { + const size_t from0 = k1 * product_1 + 2 * k - 1; + const size_t from1 = from0 + m; + const size_t from2 = from1 + m; + + const ATOMIC f0_real = VECTOR(in,istride,from0); + const ATOMIC f0_imag = VECTOR(in,istride,from0 + 1); + const ATOMIC f1_real = VECTOR(in,istride,from1); + const ATOMIC f1_imag = VECTOR(in,istride,from1 + 1); + const ATOMIC f2_real = VECTOR(in,istride,from2); + const ATOMIC f2_imag = VECTOR(in,istride,from2 + 1); + + const ATOMIC z0_real = f0_real; + const ATOMIC z0_imag = f0_imag; + const ATOMIC z1_real = w1_real * f1_real - w1_imag * f1_imag; + const ATOMIC z1_imag = w1_real * f1_imag + w1_imag * f1_real; + const ATOMIC z2_real = w2_real * f2_real - w2_imag * f2_imag; + const ATOMIC z2_imag = w2_real * f2_imag + w2_imag * f2_real; + + /* compute x = W(3) z */ + + /* t1 = z1 + z2 */ + const ATOMIC t1_real = z1_real + z2_real; + const ATOMIC t1_imag = z1_imag + z2_imag; + + /* t2 = z0 - t1/2 */ + const ATOMIC t2_real = z0_real - t1_real / 2; + const ATOMIC t2_imag = z0_imag - t1_imag / 2; + + /* t3 = (+/-) sin(pi/3)*(z1 - z2) */ + const ATOMIC t3_real = -tau * (z1_real - z2_real); + const ATOMIC t3_imag = -tau * (z1_imag - z2_imag); + + /* x0 = z0 + t1 */ + const ATOMIC x0_real = z0_real + t1_real; + const ATOMIC x0_imag = z0_imag + t1_imag; + + /* x1 = t2 + i t3 */ + const ATOMIC x1_real = t2_real - t3_imag; + const ATOMIC x1_imag = t2_imag + t3_real; + + /* x2 = t2 - i t3 */ + const ATOMIC x2_real = t2_real + t3_imag; + const ATOMIC x2_imag = t2_imag - t3_real; + + /* apply twiddle factors */ + + const size_t to0 = k1 * product + 2 * k - 1; + const size_t to1 = to0 + 2 * product_1; + const size_t to2 = 2 * product_1 - 2 * k + k1 * product - 1; + + /* to0 = 1 * x0 */ + VECTOR(out,ostride,to0) = x0_real; + VECTOR(out,ostride,to0 + 1) = x0_imag; + + /* to1 = 1 * x1 */ + VECTOR(out,ostride,to1) = x1_real; + VECTOR(out,ostride,to1 + 1) = x1_imag; + + /* to2 = 1 * x2 */ + VECTOR(out,ostride,to2) = x2_real; + VECTOR(out,ostride,to2 + 1) = -x2_imag; + } + } + + if (product_1 % 2 == 1) + return; + + for (k1 = 0; k1 < q; k1++) + { + const size_t from0 = k1 * product_1 + product_1 - 1; + const size_t from1 = from0 + m; + const size_t from2 = from1 + m; + + const ATOMIC z0_real = VECTOR(in,istride,from0); + const ATOMIC z1_real = VECTOR(in,istride,from1); + const ATOMIC z2_real = VECTOR(in,istride,from2); + + const ATOMIC t1 = z1_real - z2_real; + const ATOMIC x0_real = z0_real + t1 / 2.0; + const ATOMIC x0_imag = -tau * (z1_real + z2_real); + const ATOMIC x1_real = z0_real - t1; + + const size_t to0 = k1 * product + product_1 - 1; + const size_t to1 = to0 + 2 * product_1; + + VECTOR(out,ostride,to0) = x0_real; + VECTOR(out,ostride,to0 + 1) = x0_imag; + VECTOR(out,ostride,to1) = x1_real; + } + + return; +} |