108 lines
2.8 KiB
C
108 lines
2.8 KiB
C
/* mpz_congruent_ui_p -- test congruence of mpz and ulong.
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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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/* There's some explicit checks for c<d since it seems reasonably likely an
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application might use that in a test.
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Hopefully the compiler can generate something good for r==(c%d), though
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if modexact is being used exclusively then that's not reached. */
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int
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mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du)
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{
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mp_srcptr ap;
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mp_size_t asize;
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mp_limb_t c, d, r;
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if (UNLIKELY (du == 0))
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return (mpz_cmp_ui (a, cu) == 0);
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asize = SIZ(a);
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if (asize == 0)
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{
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if (cu < du)
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return cu == 0;
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else
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return (cu % du) == 0;
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}
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/* For nails don't try to be clever if c or d is bigger than a limb, just
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fake up some mpz_t's and go to the main mpz_congruent_p. */
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if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX)
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{
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mp_limb_t climbs[2], dlimbs[2];
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mpz_t cz, dz;
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ALLOC(cz) = 2;
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PTR(cz) = climbs;
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ALLOC(dz) = 2;
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PTR(dz) = dlimbs;
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mpz_set_ui (cz, cu);
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mpz_set_ui (dz, du);
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return mpz_congruent_p (a, cz, dz);
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}
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/* NEG_MOD works on limbs, so convert ulong to limb */
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c = cu;
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d = du;
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if (asize < 0)
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{
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asize = -asize;
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NEG_MOD (c, c, d);
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}
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ap = PTR (a);
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if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD))
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{
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r = mpn_mod_1 (ap, asize, d);
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if (c < d)
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return r == c;
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else
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return r == (c % d);
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}
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if ((d & 1) == 0)
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{
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/* Strip low zero bits to get odd d required by modexact. If
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d==e*2^n then a==c mod d if and only if both a==c mod 2^n
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and a==c mod e. */
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unsigned twos;
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if ((ap[0]-c) & LOW_ZEROS_MASK (d))
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return 0;
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count_trailing_zeros (twos, d);
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d >>= twos;
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}
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r = mpn_modexact_1c_odd (ap, asize, d, c);
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return r == 0 || r == d;
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}
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