Annotation of OpenXM_contrib/gmp/mpz/remove.c, Revision 1.1.1.1
1.1 maekawa 1: /* mpz_remove -- divide out a factor and return its multiplicity.
2:
3: Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
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: #if __STDC__
27: mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
28: #else
29: mpz_remove (dest, src, f)
30: mpz_ptr dest;
31: mpz_srcptr src;
32: mpz_srcptr f;
33: #endif
34: {
35: mpz_t fpow[40]; /* inexhaustible...until year 2020 or so */
36: mpz_t x, rem;
37: unsigned long int pwr;
38: int p;
39:
40: if (mpz_cmp_ui (f, 1) <= 0 || mpz_sgn (src) == 0)
41: DIVIDE_BY_ZERO;
42: if (mpz_cmp_ui (f, 2) == 0)
43: {
44: unsigned long int s0;
45: s0 = mpz_scan1 (src, 0);
46: mpz_div_2exp (dest, src, s0);
47: return s0;
48: }
49:
50: /* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0). It is an
51: upper bound of the result we're seeking. We could also shift down the
52: operands so that they become odd, to make intermediate values smaller. */
53:
54: mpz_init (rem);
55: mpz_init (x);
56:
57: pwr = 0;
58: mpz_init (fpow[0]);
59: mpz_set (fpow[0], f);
60: mpz_set (dest, src);
61:
62: /* Divide by f, f^2, ..., f^(2^k) until we get a remainder for f^(2^k). */
63: for (p = 0;; p++)
64: {
65: mpz_tdiv_qr (x, rem, dest, fpow[p]);
66: if (SIZ (rem) != 0)
67: break;
68: mpz_init (fpow[p + 1]);
69: mpz_mul (fpow[p + 1], fpow[p], fpow[p]);
70: mpz_set (dest, x);
71: }
72:
73: pwr = (1 << p) - 1;
74:
75: mpz_clear (fpow[p]);
76:
77: /* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give a
78: zero remainder. */
79: while (--p >= 0)
80: {
81: mpz_tdiv_qr (x, rem, dest, fpow[p]);
82: if (SIZ (rem) == 0)
83: {
84: pwr += 1 << p;
85: mpz_set (dest, x);
86: }
87: mpz_clear (fpow[p]);
88: }
89:
90: mpz_clear (x);
91: mpz_clear (rem);
92: return pwr;
93: }
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