| Austin Schuh | dace2a6 | 2020-08-18 10:56:48 -0700 | [diff] [blame^] | 1 | /* mpz_divisible_ui_p -- mpz by ulong divisibility test. |
| 2 | |
| 3 | Copyright 2000-2002 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 | int |
| 36 | mpz_divisible_ui_p (mpz_srcptr a, unsigned long d) |
| 37 | { |
| 38 | mp_size_t asize; |
| 39 | mp_ptr ap; |
| 40 | unsigned twos; |
| 41 | |
| 42 | asize = SIZ(a); |
| 43 | if (UNLIKELY (d == 0)) |
| 44 | return (asize == 0); |
| 45 | |
| 46 | if (asize == 0) /* 0 divisible by any d */ |
| 47 | return 1; |
| 48 | |
| 49 | /* For nails don't try to be clever if d is bigger than a limb, just fake |
| 50 | up an mpz_t and go to the main mpz_divisible_p. */ |
| 51 | if (d > GMP_NUMB_MAX) |
| 52 | { |
| 53 | mp_limb_t dlimbs[2]; |
| 54 | mpz_t dz; |
| 55 | ALLOC(dz) = 2; |
| 56 | PTR(dz) = dlimbs; |
| 57 | mpz_set_ui (dz, d); |
| 58 | return mpz_divisible_p (a, dz); |
| 59 | } |
| 60 | |
| 61 | ap = PTR(a); |
| 62 | asize = ABS(asize); /* ignore sign of a */ |
| 63 | |
| 64 | if (ABOVE_THRESHOLD (asize, BMOD_1_TO_MOD_1_THRESHOLD)) |
| 65 | return mpn_mod_1 (ap, asize, (mp_limb_t) d) == 0; |
| 66 | |
| 67 | if (! (d & 1)) |
| 68 | { |
| 69 | /* Strip low zero bits to get odd d required by modexact. If d==e*2^n |
| 70 | and a is divisible by 2^n and by e, then it's divisible by d. */ |
| 71 | |
| 72 | if ((ap[0] & LOW_ZEROS_MASK (d)) != 0) |
| 73 | return 0; |
| 74 | |
| 75 | count_trailing_zeros (twos, (mp_limb_t) d); |
| 76 | d >>= twos; |
| 77 | } |
| 78 | |
| 79 | return mpn_modexact_1_odd (ap, asize, (mp_limb_t) d) == 0; |
| 80 | } |