1 | /* mpz_divisible_2exp_p -- mpz by 2^n divisibility test |
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2 | |
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3 | Copyright 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 | |
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25 | |
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26 | int |
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27 | mpz_divisible_2exp_p (mpz_srcptr a, unsigned long d) |
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28 | { |
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29 | unsigned long i, dlimbs, dbits; |
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30 | mp_ptr ap; |
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31 | mp_limb_t dmask; |
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32 | mp_size_t asize; |
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33 | |
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34 | asize = ABSIZ(a); |
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35 | dlimbs = d / GMP_NUMB_BITS; |
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36 | |
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37 | /* if d covers the whole of a, then only a==0 is divisible */ |
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38 | if (asize <= dlimbs) |
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39 | return asize == 0; |
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40 | |
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41 | /* whole limbs must be zero */ |
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42 | ap = PTR(a); |
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43 | for (i = 0; i < dlimbs; i++) |
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44 | if (ap[i] != 0) |
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45 | return 0; |
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46 | |
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47 | /* left over bits must be zero */ |
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48 | dbits = d % GMP_NUMB_BITS; |
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49 | dmask = (CNST_LIMB(1) << dbits) - 1; |
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50 | return (ap[dlimbs] & dmask) == 0; |
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51 | } |
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