| /* 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; |
| } |