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- /* fft/factorize.c
- *
- * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 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 3 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.
- */
- #include "gsl__config.h"
- #include "gsl_errno.h"
- #include "gsl_fft_complex.h"
- #include "gsl_fft__factorize.h"
- static int
- fft_complex_factorize (const size_t n,
- size_t *nf,
- size_t factors[])
- {
- const size_t complex_subtransforms[] =
- {7, 6, 5, 4, 3, 2, 0};
- /* other factors can be added here if their transform modules are
- implemented. The end of the list is marked by 0. */
- int status = fft_factorize (n, complex_subtransforms, nf, factors);
- return status;
- }
- static int
- fft_halfcomplex_factorize (const size_t n,
- size_t *nf,
- size_t factors[])
- {
- const size_t halfcomplex_subtransforms[] =
- {5, 4, 3, 2, 0};
- int status = fft_factorize (n, halfcomplex_subtransforms, nf, factors);
- return status;
- }
- static int
- fft_real_factorize (const size_t n,
- size_t *nf,
- size_t factors[])
- {
- const size_t real_subtransforms[] =
- {5, 4, 3, 2, 0};
- int status = fft_factorize (n, real_subtransforms, nf, factors);
- return status;
- }
- static int
- fft_factorize (const size_t n,
- const size_t implemented_subtransforms[],
- size_t *n_factors,
- size_t factors[])
- {
- size_t nf = 0;
- size_t ntest = n;
- size_t factor;
- size_t i = 0;
- if (n == 0)
- {
- GSL_ERROR ("length n must be positive integer", GSL_EDOM);
- }
- if (n == 1)
- {
- factors[0] = 1;
- *n_factors = 1;
- return 0;
- }
- /* deal with the implemented factors first */
- while (implemented_subtransforms[i] && ntest != 1)
- {
- factor = implemented_subtransforms[i];
- while ((ntest % factor) == 0)
- {
- ntest = ntest / factor;
- factors[nf] = factor;
- nf++;
- }
- i++;
- }
- /* deal with any other even prime factors (there is only one) */
- factor = 2;
- while ((ntest % factor) == 0 && (ntest != 1))
- {
- ntest = ntest / factor;
- factors[nf] = factor;
- nf++;
- }
- /* deal with any other odd prime factors */
- factor = 3;
- while (ntest != 1)
- {
- while ((ntest % factor) != 0)
- {
- factor += 2;
- }
- ntest = ntest / factor;
- factors[nf] = factor;
- nf++;
- }
- /* check that the factorization is correct */
- {
- size_t product = 1;
- for (i = 0; i < nf; i++)
- {
- product *= factors[i];
- }
- if (product != n)
- {
- GSL_ERROR ("factorization failed", GSL_ESANITY);
- }
- }
- *n_factors = nf;
- return 0;
- }
- static int
- fft_binary_logn (const size_t n)
- {
- size_t ntest ;
- size_t binary_logn = 0 ;
- size_t k = 1;
- while (k < n)
- {
- k *= 2;
- binary_logn++;
- }
- ntest = (1 << binary_logn) ;
- if (n != ntest )
- {
- return -1 ; /* n is not a power of 2 */
- }
- return binary_logn;
- }
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