1*86d7f5d3SJohn Marino /* mpz_remove -- divide out a factor and return its multiplicity.
2*86d7f5d3SJohn Marino
3*86d7f5d3SJohn Marino Copyright 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
4*86d7f5d3SJohn Marino
5*86d7f5d3SJohn Marino This file is part of the GNU MP Library.
6*86d7f5d3SJohn Marino
7*86d7f5d3SJohn Marino The GNU MP Library is free software; you can redistribute it and/or modify
8*86d7f5d3SJohn Marino it under the terms of the GNU Lesser General Public License as published by
9*86d7f5d3SJohn Marino the Free Software Foundation; either version 3 of the License, or (at your
10*86d7f5d3SJohn Marino option) any later version.
11*86d7f5d3SJohn Marino
12*86d7f5d3SJohn Marino The GNU MP Library is distributed in the hope that it will be useful, but
13*86d7f5d3SJohn Marino WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14*86d7f5d3SJohn Marino or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
15*86d7f5d3SJohn Marino License for more details.
16*86d7f5d3SJohn Marino
17*86d7f5d3SJohn Marino You should have received a copy of the GNU Lesser General Public License
18*86d7f5d3SJohn Marino along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
19*86d7f5d3SJohn Marino
20*86d7f5d3SJohn Marino #include "gmp.h"
21*86d7f5d3SJohn Marino #include "gmp-impl.h"
22*86d7f5d3SJohn Marino
23*86d7f5d3SJohn Marino mp_bitcnt_t
mpz_remove(mpz_ptr dest,mpz_srcptr src,mpz_srcptr f)24*86d7f5d3SJohn Marino mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
25*86d7f5d3SJohn Marino {
26*86d7f5d3SJohn Marino mpz_t fpow[GMP_LIMB_BITS]; /* Really MP_SIZE_T_BITS */
27*86d7f5d3SJohn Marino mpz_t x, rem;
28*86d7f5d3SJohn Marino mp_bitcnt_t pwr;
29*86d7f5d3SJohn Marino int p;
30*86d7f5d3SJohn Marino
31*86d7f5d3SJohn Marino if (mpz_cmp_ui (f, 1) <= 0)
32*86d7f5d3SJohn Marino DIVIDE_BY_ZERO;
33*86d7f5d3SJohn Marino
34*86d7f5d3SJohn Marino if (SIZ (src) == 0)
35*86d7f5d3SJohn Marino {
36*86d7f5d3SJohn Marino if (src != dest)
37*86d7f5d3SJohn Marino mpz_set (dest, src);
38*86d7f5d3SJohn Marino return 0;
39*86d7f5d3SJohn Marino }
40*86d7f5d3SJohn Marino
41*86d7f5d3SJohn Marino if (mpz_cmp_ui (f, 2) == 0)
42*86d7f5d3SJohn Marino {
43*86d7f5d3SJohn Marino mp_bitcnt_t s0;
44*86d7f5d3SJohn Marino s0 = mpz_scan1 (src, 0);
45*86d7f5d3SJohn Marino mpz_div_2exp (dest, src, s0);
46*86d7f5d3SJohn Marino return s0;
47*86d7f5d3SJohn Marino }
48*86d7f5d3SJohn Marino
49*86d7f5d3SJohn Marino /* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0). It is an
50*86d7f5d3SJohn Marino upper bound of the result we're seeking. We could also shift down the
51*86d7f5d3SJohn Marino operands so that they become odd, to make intermediate values smaller. */
52*86d7f5d3SJohn Marino
53*86d7f5d3SJohn Marino mpz_init (rem);
54*86d7f5d3SJohn Marino mpz_init (x);
55*86d7f5d3SJohn Marino
56*86d7f5d3SJohn Marino pwr = 0;
57*86d7f5d3SJohn Marino mpz_init (fpow[0]);
58*86d7f5d3SJohn Marino mpz_set (fpow[0], f);
59*86d7f5d3SJohn Marino mpz_set (dest, src);
60*86d7f5d3SJohn Marino
61*86d7f5d3SJohn Marino /* Divide by f, f^2, ..., f^(2^k) until we get a remainder for f^(2^k). */
62*86d7f5d3SJohn Marino for (p = 0;; p++)
63*86d7f5d3SJohn Marino {
64*86d7f5d3SJohn Marino mpz_tdiv_qr (x, rem, dest, fpow[p]);
65*86d7f5d3SJohn Marino if (SIZ (rem) != 0)
66*86d7f5d3SJohn Marino break;
67*86d7f5d3SJohn Marino mpz_init (fpow[p + 1]);
68*86d7f5d3SJohn Marino mpz_mul (fpow[p + 1], fpow[p], fpow[p]);
69*86d7f5d3SJohn Marino mpz_set (dest, x);
70*86d7f5d3SJohn Marino }
71*86d7f5d3SJohn Marino
72*86d7f5d3SJohn Marino pwr = (1L << p) - 1;
73*86d7f5d3SJohn Marino
74*86d7f5d3SJohn Marino mpz_clear (fpow[p]);
75*86d7f5d3SJohn Marino
76*86d7f5d3SJohn Marino /* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give a
77*86d7f5d3SJohn Marino zero remainder. */
78*86d7f5d3SJohn Marino while (--p >= 0)
79*86d7f5d3SJohn Marino {
80*86d7f5d3SJohn Marino mpz_tdiv_qr (x, rem, dest, fpow[p]);
81*86d7f5d3SJohn Marino if (SIZ (rem) == 0)
82*86d7f5d3SJohn Marino {
83*86d7f5d3SJohn Marino pwr += 1L << p;
84*86d7f5d3SJohn Marino mpz_set (dest, x);
85*86d7f5d3SJohn Marino }
86*86d7f5d3SJohn Marino mpz_clear (fpow[p]);
87*86d7f5d3SJohn Marino }
88*86d7f5d3SJohn Marino
89*86d7f5d3SJohn Marino mpz_clear (x);
90*86d7f5d3SJohn Marino mpz_clear (rem);
91*86d7f5d3SJohn Marino return pwr;
92*86d7f5d3SJohn Marino }
93