| /* 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" |
| |
| unsigned long int |
| mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f) |
| { |
| mpz_t fpow[40]; /* inexhaustible...until year 2020 or so */ |
| mpz_t x, rem; |
| unsigned long int 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) |
| { |
| unsigned long int 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 = (1 << 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 += 1 << p; |
| mpz_set (dest, x); |
| } |
| mpz_clear (fpow[p]); |
| } |
| |
| mpz_clear (x); |
| mpz_clear (rem); |
| return pwr; |
| } |