Annotation of OpenXM_contrib/gmp/mpz/remove.c, Revision 1.1.1.2
1.1 maekawa 1: /* mpz_remove -- divide out a factor and return its multiplicity.
2:
1.1.1.2 ! ohara 3: Copyright 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
1.1 maekawa 4:
5: This file is part of the GNU MP Library.
6:
7: The GNU MP Library is free software; you can redistribute it and/or modify
8: it under the terms of the GNU Lesser General Public License as published by
9: the Free Software Foundation; either version 2.1 of the License, or (at your
10: option) any later version.
11:
12: The GNU MP Library is distributed in the hope that it will be useful, but
13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
15: License for more details.
16:
17: You should have received a copy of the GNU Lesser General Public License
18: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20: MA 02111-1307, USA. */
21:
22: #include "gmp.h"
23: #include "gmp-impl.h"
24:
25: unsigned long int
26: mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
27: {
28: mpz_t fpow[40]; /* inexhaustible...until year 2020 or so */
29: mpz_t x, rem;
30: unsigned long int pwr;
31: int p;
32:
1.1.1.2 ! ohara 33: if (mpz_cmp_ui (f, 1) <= 0)
1.1 maekawa 34: DIVIDE_BY_ZERO;
1.1.1.2 ! ohara 35:
! 36: if (SIZ (src) == 0)
! 37: {
! 38: if (src != dest)
! 39: mpz_set (dest, src);
! 40: return 0;
! 41: }
! 42:
1.1 maekawa 43: if (mpz_cmp_ui (f, 2) == 0)
44: {
45: unsigned long int s0;
46: s0 = mpz_scan1 (src, 0);
47: mpz_div_2exp (dest, src, s0);
48: return s0;
49: }
50:
51: /* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0). It is an
52: upper bound of the result we're seeking. We could also shift down the
53: operands so that they become odd, to make intermediate values smaller. */
54:
55: mpz_init (rem);
56: mpz_init (x);
57:
58: pwr = 0;
59: mpz_init (fpow[0]);
60: mpz_set (fpow[0], f);
61: mpz_set (dest, src);
62:
63: /* Divide by f, f^2, ..., f^(2^k) until we get a remainder for f^(2^k). */
64: for (p = 0;; p++)
65: {
66: mpz_tdiv_qr (x, rem, dest, fpow[p]);
67: if (SIZ (rem) != 0)
68: break;
69: mpz_init (fpow[p + 1]);
70: mpz_mul (fpow[p + 1], fpow[p], fpow[p]);
71: mpz_set (dest, x);
72: }
73:
74: pwr = (1 << p) - 1;
75:
76: mpz_clear (fpow[p]);
77:
78: /* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give a
79: zero remainder. */
80: while (--p >= 0)
81: {
82: mpz_tdiv_qr (x, rem, dest, fpow[p]);
83: if (SIZ (rem) == 0)
84: {
85: pwr += 1 << p;
86: mpz_set (dest, x);
87: }
88: mpz_clear (fpow[p]);
89: }
90:
91: mpz_clear (x);
92: mpz_clear (rem);
93: return pwr;
94: }
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