| 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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