| 1 | /* mpz_divisible_ui_p -- mpz by ulong divisibility test. |
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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 | int |
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| 28 | mpz_divisible_ui_p (mpz_srcptr a, unsigned long d) |
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| 29 | { |
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| 30 | mp_size_t asize; |
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| 31 | mp_ptr ap; |
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| 32 | unsigned twos; |
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| 33 | |
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| 34 | if (d == 0) |
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| 35 | DIVIDE_BY_ZERO; |
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| 36 | |
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| 37 | asize = SIZ(a); |
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| 38 | if (asize == 0) /* 0 divisible by any d */ |
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| 39 | return 1; |
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| 40 | |
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| 41 | /* For nails don't try to be clever if d is bigger than a limb, just fake |
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| 42 | up an mpz_t and go to the main mpz_divisible_p. */ |
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| 43 | if (d > GMP_NUMB_MAX) |
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| 44 | { |
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| 45 | mp_limb_t dlimbs[2]; |
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| 46 | mpz_t dz; |
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| 47 | ALLOC(dz) = 2; |
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| 48 | PTR(dz) = dlimbs; |
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| 49 | mpz_set_ui (dz, d); |
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| 50 | return mpz_divisible_p (a, dz); |
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| 51 | } |
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| 52 | |
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| 53 | ap = PTR(a); |
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| 54 | asize = ABS(asize); /* ignore sign of a */ |
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| 55 | |
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| 56 | if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD)) |
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| 57 | return mpn_mod_1 (ap, asize, (mp_limb_t) d) == 0; |
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| 58 | |
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| 59 | if (! (d & 1)) |
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| 60 | { |
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| 61 | /* Strip low zero bits to get odd d required by modexact. If d==e*2^n |
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| 62 | and a is divisible by 2^n and by e, then it's divisible by d. */ |
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| 63 | |
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| 64 | if ((ap[0] & LOW_ZEROS_MASK (d)) != 0) |
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| 65 | return 0; |
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| 66 | |
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| 67 | count_trailing_zeros (twos, (mp_limb_t) d); |
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| 68 | d >>= twos; |
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| 69 | } |
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| 70 | |
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| 71 | return mpn_modexact_1_odd (ap, asize, (mp_limb_t) d) == 0; |
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| 72 | } |
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