| 1 | /* mpz_congruent_ui_p -- test congruence of mpz and ulong. |
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| 2 | |
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| 3 | Copyright 2000, 2001, 2002 Free Software Foundation, Inc. |
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| 4 | |
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| 5 | This file is part of the GNU MP Library. |
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| 6 | |
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| 7 | The GNU MP Library is free software; you can redistribute it and/or modify |
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| 8 | it under the terms of the GNU Lesser General Public License as published by |
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| 9 | the Free Software Foundation; either version 2.1 of the License, or (at your |
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| 10 | option) any later version. |
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| 11 | |
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| 12 | The GNU MP Library is distributed in the hope that it will be useful, but |
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| 13 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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| 14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
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| 15 | License for more details. |
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| 16 | |
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| 17 | You should have received a copy of the GNU Lesser General Public License |
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| 18 | along with the GNU MP Library; see the file COPYING.LIB. If not, write to |
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| 19 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
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| 20 | MA 02111-1307, USA. */ |
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| 21 | |
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| 22 | #include "gmp.h" |
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| 23 | #include "gmp-impl.h" |
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| 24 | #include "longlong.h" |
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| 25 | |
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| 26 | |
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| 27 | /* There's some explicit checks for c<d since it seems reasonably likely an |
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| 28 | application might use that in a test. |
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| 29 | |
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| 30 | Hopefully the compiler can generate something good for r==(c%d), though |
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| 31 | if modexact is being used exclusively then that's not reached. */ |
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| 32 | |
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| 33 | int |
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| 34 | mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du) |
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| 35 | { |
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| 36 | mp_srcptr ap; |
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| 37 | mp_size_t asize; |
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| 38 | mp_limb_t c, d, r; |
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| 39 | |
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| 40 | if (du == 0) |
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| 41 | DIVIDE_BY_ZERO; |
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| 42 | |
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| 43 | asize = SIZ(a); |
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| 44 | if (asize == 0) |
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| 45 | { |
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| 46 | if (cu < du) |
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| 47 | return cu == 0; |
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| 48 | else |
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| 49 | return (cu % du) == 0; |
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| 50 | } |
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| 51 | |
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| 52 | /* For nails don't try to be clever if c or d is bigger than a limb, just |
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| 53 | fake up some mpz_t's and go to the main mpz_congruent_p. */ |
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| 54 | if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX) |
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| 55 | { |
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| 56 | mp_limb_t climbs[2], dlimbs[2]; |
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| 57 | mpz_t cz, dz; |
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| 58 | |
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| 59 | ALLOC(cz) = 2; |
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| 60 | PTR(cz) = climbs; |
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| 61 | ALLOC(dz) = 2; |
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| 62 | PTR(dz) = dlimbs; |
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| 63 | |
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| 64 | mpz_set_ui (cz, cu); |
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| 65 | mpz_set_ui (dz, du); |
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| 66 | return mpz_congruent_p (a, cz, dz); |
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| 67 | } |
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| 68 | |
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| 69 | /* NEG_MOD works on limbs, so convert ulong to limb */ |
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| 70 | c = cu; |
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| 71 | d = du; |
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| 72 | |
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| 73 | if (asize < 0) |
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| 74 | { |
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| 75 | asize = -asize; |
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| 76 | NEG_MOD (c, c, d); |
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| 77 | } |
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| 78 | |
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| 79 | ap = PTR (a); |
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| 80 | |
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| 81 | if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD)) |
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| 82 | { |
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| 83 | r = mpn_mod_1 (ap, asize, d); |
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| 84 | if (c < d) |
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| 85 | return r == c; |
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| 86 | else |
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| 87 | return r == (c % d); |
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| 88 | } |
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| 89 | |
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| 90 | if ((d & 1) == 0) |
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| 91 | { |
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| 92 | /* Strip low zero bits to get odd d required by modexact. If |
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| 93 | d==e*2^n then a==c mod d if and only if both a==c mod 2^n |
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| 94 | and a==c mod e. */ |
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| 95 | |
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| 96 | unsigned twos; |
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| 97 | |
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| 98 | if ((ap[0]-c) & LOW_ZEROS_MASK (d)) |
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| 99 | return 0; |
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| 100 | |
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| 101 | count_trailing_zeros (twos, d); |
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| 102 | d >>= twos; |
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| 103 | } |
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| 104 | |
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| 105 | r = mpn_modexact_1c_odd (ap, asize, d, c); |
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| 106 | return r == 0 || r == d; |
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| 107 | } |
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