cong_ui.c
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上传日期:2022-08-06
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- /* mpz_congruent_ui_p -- test congruence of mpz and ulong.
- Copyright 2000, 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"
- #include "longlong.h"
- /* There's some explicit checks for c<d since it seems reasonably likely an
- application might use that in a test.
- Hopefully the compiler can generate something good for r==(c%d), though
- if modexact is being used exclusively then that's not reached. */
- int
- mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du)
- {
- mp_srcptr ap;
- mp_size_t asize;
- mp_limb_t c, d, r;
- if (UNLIKELY (du == 0))
- return (mpz_cmp_ui (a, cu) == 0);
- asize = SIZ(a);
- if (asize == 0)
- {
- if (cu < du)
- return cu == 0;
- else
- return (cu % du) == 0;
- }
- /* For nails don't try to be clever if c or d is bigger than a limb, just
- fake up some mpz_t's and go to the main mpz_congruent_p. */
- if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX)
- {
- mp_limb_t climbs[2], dlimbs[2];
- mpz_t cz, dz;
- ALLOC(cz) = 2;
- PTR(cz) = climbs;
- ALLOC(dz) = 2;
- PTR(dz) = dlimbs;
- mpz_set_ui (cz, cu);
- mpz_set_ui (dz, du);
- return mpz_congruent_p (a, cz, dz);
- }
- /* NEG_MOD works on limbs, so convert ulong to limb */
- c = cu;
- d = du;
- if (asize < 0)
- {
- asize = -asize;
- NEG_MOD (c, c, d);
- }
- ap = PTR (a);
- if (ABOVE_THRESHOLD (asize, BMOD_1_TO_MOD_1_THRESHOLD))
- {
- r = mpn_mod_1 (ap, asize, d);
- if (c < d)
- return r == c;
- else
- return r == (c % d);
- }
- if ((d & 1) == 0)
- {
- /* Strip low zero bits to get odd d required by modexact. If
- d==e*2^n then a==c mod d if and only if both a==c mod 2^n
- and a==c mod e. */
- unsigned twos;
- if ((ap[0]-c) & LOW_ZEROS_MASK (d))
- return 0;
- count_trailing_zeros (twos, d);
- d >>= twos;
- }
- r = mpn_modexact_1c_odd (ap, asize, d, c);
- return r == 0 || r == d;
- }