remove.c
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上传日期:2022-08-06
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- /* mpz_remove -- divide out a factor and return its multiplicity.
- Copyright 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
- This file is part of the GNU MP Library.
- The GNU MP Library is free software; you can redistribute it and/or modify
- it under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, or (at your
- option) any later version.
- The GNU MP Library 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 Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include "gmp.h"
- #include "gmp-impl.h"
- mp_bitcnt_t
- mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
- {
- mpz_t fpow[GMP_LIMB_BITS]; /* Really MP_SIZE_T_BITS */
- mpz_t x, rem;
- mp_bitcnt_t pwr;
- int p;
- if (mpz_cmp_ui (f, 1) <= 0)
- DIVIDE_BY_ZERO;
- if (SIZ (src) == 0)
- {
- if (src != dest)
- mpz_set (dest, src);
- return 0;
- }
- if (mpz_cmp_ui (f, 2) == 0)
- {
- mp_bitcnt_t s0;
- s0 = mpz_scan1 (src, 0);
- mpz_div_2exp (dest, src, s0);
- return s0;
- }
- /* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0). It is an
- upper bound of the result we're seeking. We could also shift down the
- operands so that they become odd, to make intermediate values smaller. */
- mpz_init (rem);
- mpz_init (x);
- pwr = 0;
- mpz_init (fpow[0]);
- mpz_set (fpow[0], f);
- mpz_set (dest, src);
- /* Divide by f, f^2, ..., f^(2^k) until we get a remainder for f^(2^k). */
- for (p = 0;; p++)
- {
- mpz_tdiv_qr (x, rem, dest, fpow[p]);
- if (SIZ (rem) != 0)
- break;
- mpz_init (fpow[p + 1]);
- mpz_mul (fpow[p + 1], fpow[p], fpow[p]);
- mpz_set (dest, x);
- }
- pwr = (1L << p) - 1;
- mpz_clear (fpow[p]);
- /* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give a
- zero remainder. */
- while (--p >= 0)
- {
- mpz_tdiv_qr (x, rem, dest, fpow[p]);
- if (SIZ (rem) == 0)
- {
- pwr += 1L << p;
- mpz_set (dest, x);
- }
- mpz_clear (fpow[p]);
- }
- mpz_clear (x);
- mpz_clear (rem);
- return pwr;
- }