Annotation of OpenXM_contrib/gmp/mpz/divis_2exp.c, Revision 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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