52 lines
1.5 KiB
C
52 lines
1.5 KiB
C
/* mpz_divisible_2exp_p -- mpz by 2^n divisibility test
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Copyright 2001, 2002 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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int
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mpz_divisible_2exp_p (mpz_srcptr a, unsigned long d)
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{
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unsigned long i, dlimbs, dbits;
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mp_ptr ap;
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mp_limb_t dmask;
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mp_size_t asize;
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asize = ABSIZ(a);
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dlimbs = d / GMP_NUMB_BITS;
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/* if d covers the whole of a, then only a==0 is divisible */
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if (asize <= dlimbs)
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return asize == 0;
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/* whole limbs must be zero */
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ap = PTR(a);
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for (i = 0; i < dlimbs; i++)
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if (ap[i] != 0)
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return 0;
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/* left over bits must be zero */
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dbits = d % GMP_NUMB_BITS;
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dmask = (CNST_LIMB(1) << dbits) - 1;
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return (ap[dlimbs] & dmask) == 0;
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}
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