diff options
Diffstat (limited to 'gsl-1.9/fft/c_pass_3.c')
| -rw-r--r-- | gsl-1.9/fft/c_pass_3.c | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/gsl-1.9/fft/c_pass_3.c b/gsl-1.9/fft/c_pass_3.c new file mode 100644 index 0000000..f55fb5c --- /dev/null +++ b/gsl-1.9/fft/c_pass_3.c @@ -0,0 +1,127 @@ +/* fft/c_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 int +FUNCTION(fft_complex,pass_3) (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) +{ + size_t i = 0, j = 0; + 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 size_t jump = (factor - 1) * product_1; + + const ATOMIC tau = sqrt (3.0) / 2.0; + + for (k = 0; k < q; k++) + { + ATOMIC w1_real, w1_imag, w2_real, w2_imag; + + if (k == 0) + { + w1_real = 1.0; + w1_imag = 0.0; + w2_real = 1.0; + w2_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]); + } + 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]); + } + } + + 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); + const ATOMIC z2_real = REAL(in,istride,i+2*m); + const ATOMIC z2_imag = IMAG(in,istride,i+2*m); + + /* 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 / 2.0; + const ATOMIC t2_imag = z0_imag - t1_imag / 2.0; + + /* t3 = (+/-) sin(pi/3)*(z1 - z2) */ + const ATOMIC t3_real = ((int) sign) * tau * (z1_real - z2_real); + const ATOMIC t3_imag = ((int) sign) * 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 */ + + /* to0 = 1 * x0 */ + REAL(out,ostride,j) = x0_real; + IMAG(out,ostride,j) = x0_imag; + + /* to1 = w1 * x1 */ + REAL(out,ostride,j+product_1) = w1_real * x1_real - w1_imag * x1_imag; + IMAG(out,ostride,j+product_1) = w1_real * x1_imag + w1_imag * x1_real; + + /* to2 = w2 * x2 */ + REAL(out,ostride,j+2*product_1) = w2_real * x2_real - w2_imag * x2_imag; + IMAG(out,ostride,j+2*product_1) = w2_real * x2_imag + w2_imag * x2_real; + + i++; j++; + } + j += jump; + } + return 0; +} |