Annotation of OpenXM_contrib/gmp/mpz/divis_2exp.c, Revision 1.1.1.1
1.1 ohara 1: /* mpz_divisible_2exp_p -- mpz by 2^n divisibility test
2:
3: Copyright 2001, 2002 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:
26: int
27: mpz_divisible_2exp_p (mpz_srcptr a, unsigned long d)
28: {
29: unsigned long i, dlimbs, dbits;
30: mp_ptr ap;
31: mp_limb_t dmask;
32: mp_size_t asize;
33:
34: asize = ABSIZ(a);
35: dlimbs = d / GMP_NUMB_BITS;
36:
37: /* if d covers the whole of a, then only a==0 is divisible */
38: if (asize <= dlimbs)
39: return asize == 0;
40:
41: /* whole limbs must be zero */
42: ap = PTR(a);
43: for (i = 0; i < dlimbs; i++)
44: if (ap[i] != 0)
45: return 0;
46:
47: /* left over bits must be zero */
48: dbits = d % GMP_NUMB_BITS;
49: dmask = (CNST_LIMB(1) << dbits) - 1;
50: return (ap[dlimbs] & dmask) == 0;
51: }
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