1 | /* mpz_lucnum2_ui -- calculate Lucas numbers. |
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2 | |
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3 | Copyright 2001 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 <stdio.h> |
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23 | #include "gmp.h" |
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24 | #include "gmp-impl.h" |
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25 | |
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26 | |
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27 | void |
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28 | mpz_lucnum2_ui (mpz_ptr ln, mpz_ptr lnsub1, unsigned long n) |
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29 | { |
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30 | mp_ptr lp, l1p, f1p; |
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31 | mp_size_t size; |
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32 | mp_limb_t c; |
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33 | TMP_DECL (marker); |
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34 | |
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35 | ASSERT (ln != lnsub1); |
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36 | |
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37 | /* handle small n quickly, and hide the special case for L[-1]=-1 */ |
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38 | if (n <= FIB_TABLE_LUCNUM_LIMIT) |
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39 | { |
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40 | mp_limb_t f = FIB_TABLE (n); |
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41 | mp_limb_t f1 = FIB_TABLE ((int) n - 1); |
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42 | |
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43 | /* L[n] = F[n] + 2F[n-1] */ |
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44 | PTR(ln)[0] = f + 2*f1; |
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45 | SIZ(ln) = 1; |
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46 | |
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47 | /* L[n-1] = 2F[n] - F[n-1], but allow for L[-1]=-1 */ |
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48 | PTR(lnsub1)[0] = (n == 0 ? 1 : 2*f - f1); |
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49 | SIZ(lnsub1) = (n == 0 ? -1 : 1); |
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50 | |
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51 | return; |
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52 | } |
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53 | |
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54 | TMP_MARK (marker); |
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55 | size = MPN_FIB2_SIZE (n); |
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56 | f1p = TMP_ALLOC_LIMBS (size); |
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57 | |
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58 | MPZ_REALLOC (ln, size+1); |
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59 | MPZ_REALLOC (lnsub1, size+1); |
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60 | lp = PTR(ln); |
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61 | l1p = PTR(lnsub1); |
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62 | |
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63 | size = mpn_fib2_ui (l1p, f1p, n); |
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64 | |
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65 | /* L[n] = F[n] + 2F[n-1] */ |
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66 | c = mpn_lshift (lp, f1p, size, 1); |
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67 | c += mpn_add_n (lp, lp, l1p, size); |
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68 | lp[size] = c; |
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69 | SIZ(ln) = size + (c != 0); |
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70 | |
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71 | /* L[n-1] = 2F[n] - F[n-1] */ |
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72 | c = mpn_lshift (l1p, l1p, size, 1); |
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73 | c -= mpn_sub_n (l1p, l1p, f1p, size); |
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74 | ASSERT ((mp_limb_signed_t) c >= 0); |
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75 | l1p[size] = c; |
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76 | SIZ(lnsub1) = size + (c != 0); |
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77 | |
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78 | TMP_FREE (marker); |
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79 | } |
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