/* 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 either:
* 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.
or
* the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any
later version.
or both in parallel, as here.
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 General Public License
for more details.
You should have received copies of the GNU General Public License and the
GNU Lesser General Public License along with the GNU MP Library. If not,
see https://www.gnu.org/licenses/. */
#include "gmp-impl.h"
int
mpz_divisible_2exp_p (mpz_srcptr a, mp_bitcnt_t d) __GMP_NOTHROW
{
mp_size_t i, dlimbs;
unsigned 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;
}