73 lines
2.1 KiB
C
73 lines
2.1 KiB
C
/* mpz_divisible_ui_p -- mpz by ulong divisibility test.
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Copyright 2000, 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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#include "longlong.h"
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int
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mpz_divisible_ui_p (mpz_srcptr a, unsigned long d)
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{
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mp_size_t asize;
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mp_ptr ap;
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unsigned twos;
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asize = SIZ(a);
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if (UNLIKELY (d == 0))
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return (asize == 0);
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if (asize == 0) /* 0 divisible by any d */
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return 1;
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/* For nails don't try to be clever if d is bigger than a limb, just fake
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up an mpz_t and go to the main mpz_divisible_p. */
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if (d > GMP_NUMB_MAX)
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{
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mp_limb_t dlimbs[2];
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mpz_t dz;
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ALLOC(dz) = 2;
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PTR(dz) = dlimbs;
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mpz_set_ui (dz, d);
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return mpz_divisible_p (a, dz);
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}
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ap = PTR(a);
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asize = ABS(asize); /* ignore sign of a */
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if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD))
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return mpn_mod_1 (ap, asize, (mp_limb_t) d) == 0;
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if (! (d & 1))
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{
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/* Strip low zero bits to get odd d required by modexact. If d==e*2^n
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and a is divisible by 2^n and by e, then it's divisible by d. */
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if ((ap[0] & LOW_ZEROS_MASK (d)) != 0)
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return 0;
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count_trailing_zeros (twos, (mp_limb_t) d);
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d >>= twos;
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}
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return mpn_modexact_1_odd (ap, asize, (mp_limb_t) d) == 0;
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}
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