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/* mpz_divisible_2exp_p -- mpz by 2^n divisibility test
Copyright 2001, 2002 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.
The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
int
mpz_divisible_2exp_p (mpz_srcptr a, unsigned long d)
{
unsigned long i, dlimbs, dbits;
mp_ptr ap;
mp_limb_t dmask;
mp_size_t asize;
asize = ABSIZ(a);
dlimbs = d / GMP_NUMB_BITS;
/* if d covers the whole of a, then only a==0 is divisible */
if (asize <= dlimbs)
return asize == 0;
/* whole limbs must be zero */
ap = PTR(a);
for (i = 0; i < dlimbs; i++)
if (ap[i] != 0)
return 0;
/* left over bits must be zero */
dbits = d % GMP_NUMB_BITS;
dmask = (CNST_LIMB(1) << dbits) - 1;
return (ap[dlimbs] & dmask) == 0;
}
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