| Austin Schuh | bb1338c | 2024-06-15 19:31:16 -0700 | [diff] [blame] | 1 | /* mpz_congruent_ui_p -- test congruence of mpz and ulong. |
| 2 | |
| 3 | Copyright 2000-2002, 2012 Free Software Foundation, Inc. |
| 4 | |
| 5 | This file is part of the GNU MP Library. |
| 6 | |
| 7 | The GNU MP Library is free software; you can redistribute it and/or modify |
| 8 | it under the terms of either: |
| 9 | |
| 10 | * the GNU Lesser General Public License as published by the Free |
| 11 | Software Foundation; either version 3 of the License, or (at your |
| 12 | option) any later version. |
| 13 | |
| 14 | or |
| 15 | |
| 16 | * the GNU General Public License as published by the Free Software |
| 17 | Foundation; either version 2 of the License, or (at your option) any |
| 18 | later version. |
| 19 | |
| 20 | or both in parallel, as here. |
| 21 | |
| 22 | The GNU MP Library is distributed in the hope that it will be useful, but |
| 23 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| 24 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 25 | for more details. |
| 26 | |
| 27 | You should have received copies of the GNU General Public License and the |
| 28 | GNU Lesser General Public License along with the GNU MP Library. If not, |
| 29 | see https://www.gnu.org/licenses/. */ |
| 30 | |
| 31 | #include "gmp-impl.h" |
| 32 | #include "longlong.h" |
| 33 | |
| 34 | |
| 35 | /* There's some explicit checks for c<d since it seems reasonably likely an |
| 36 | application might use that in a test. |
| 37 | |
| 38 | Hopefully the compiler can generate something good for r==(c%d), though |
| 39 | if modexact is being used exclusively then that's not reached. */ |
| 40 | |
| 41 | int |
| 42 | mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du) |
| 43 | { |
| 44 | mp_srcptr ap; |
| 45 | mp_size_t asize; |
| 46 | mp_limb_t c, d, r; |
| 47 | |
| 48 | if (UNLIKELY (du == 0)) |
| 49 | return (mpz_cmp_ui (a, cu) == 0); |
| 50 | |
| 51 | asize = SIZ(a); |
| 52 | if (asize == 0) |
| 53 | { |
| 54 | if (cu < du) |
| 55 | return cu == 0; |
| 56 | else |
| 57 | return (cu % du) == 0; |
| 58 | } |
| 59 | |
| 60 | /* For nails don't try to be clever if c or d is bigger than a limb, just |
| 61 | fake up some mpz_t's and go to the main mpz_congruent_p. */ |
| 62 | if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX) |
| 63 | { |
| 64 | mp_limb_t climbs[2], dlimbs[2]; |
| 65 | mpz_t cz, dz; |
| 66 | |
| 67 | ALLOC(cz) = 2; |
| 68 | PTR(cz) = climbs; |
| 69 | ALLOC(dz) = 2; |
| 70 | PTR(dz) = dlimbs; |
| 71 | |
| 72 | mpz_set_ui (cz, cu); |
| 73 | mpz_set_ui (dz, du); |
| 74 | return mpz_congruent_p (a, cz, dz); |
| 75 | } |
| 76 | |
| 77 | /* NEG_MOD works on limbs, so convert ulong to limb */ |
| 78 | c = cu; |
| 79 | d = du; |
| 80 | |
| 81 | if (asize < 0) |
| 82 | { |
| 83 | asize = -asize; |
| 84 | NEG_MOD (c, c, d); |
| 85 | } |
| 86 | |
| 87 | ap = PTR (a); |
| 88 | |
| 89 | if (ABOVE_THRESHOLD (asize, BMOD_1_TO_MOD_1_THRESHOLD)) |
| 90 | { |
| 91 | r = mpn_mod_1 (ap, asize, d); |
| 92 | if (c < d) |
| 93 | return r == c; |
| 94 | else |
| 95 | return r == (c % d); |
| 96 | } |
| 97 | |
| 98 | if ((d & 1) == 0) |
| 99 | { |
| 100 | /* Strip low zero bits to get odd d required by modexact. If |
| 101 | d==e*2^n then a==c mod d if and only if both a==c mod 2^n |
| 102 | and a==c mod e. */ |
| 103 | |
| 104 | unsigned twos; |
| 105 | |
| 106 | if ((ap[0]-c) & LOW_ZEROS_MASK (d)) |
| 107 | return 0; |
| 108 | |
| 109 | count_trailing_zeros (twos, d); |
| 110 | d >>= twos; |
| 111 | } |
| 112 | |
| 113 | r = mpn_modexact_1c_odd (ap, asize, d, c); |
| 114 | return r == 0 || r == d; |
| 115 | } |