1/* mpz_lucnum2_ui -- calculate Lucas numbers. 2 3Copyright 2001, 2003, 2005, 2012, 2015, 2016, 2018 Free Software 4Foundation, Inc. 5 6This file is part of the GNU MP Library. 7 8The GNU MP Library is free software; you can redistribute it and/or modify 9it under the terms of either: 10 11 * the GNU Lesser General Public License as published by the Free 12 Software Foundation; either version 3 of the License, or (at your 13 option) any later version. 14 15or 16 17 * the GNU General Public License as published by the Free Software 18 Foundation; either version 2 of the License, or (at your option) any 19 later version. 20 21or both in parallel, as here. 22 23The GNU MP Library is distributed in the hope that it will be useful, but 24WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 25or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 26for more details. 27 28You should have received copies of the GNU General Public License and the 29GNU Lesser General Public License along with the GNU MP Library. If not, 30see https://www.gnu.org/licenses/. */ 31 32#include <stdio.h> 33#include "gmp-impl.h" 34 35 36void 37mpz_lucnum2_ui (mpz_ptr ln, mpz_ptr lnsub1, unsigned long n) 38{ 39 mp_ptr lp, l1p, f1p; 40 mp_size_t size; 41 mp_limb_t c; 42 TMP_DECL; 43 44 ASSERT (ln != lnsub1); 45 46 /* handle small n quickly, and hide the special case for L[-1]=-1 */ 47 if (n <= FIB_TABLE_LUCNUM_LIMIT) 48 { 49 mp_limb_t f = FIB_TABLE (n); 50 mp_limb_t f1 = FIB_TABLE ((int) n - 1); 51 52 /* L[n] = F[n] + 2F[n-1] */ 53 MPZ_NEWALLOC (ln, 1)[0] = f + 2*f1; 54 SIZ(ln) = 1; 55 56 /* L[n-1] = 2F[n] - F[n-1], but allow for L[-1]=-1 */ 57 MPZ_NEWALLOC (lnsub1, 1)[0] = (n == 0 ? 1 : 2*f - f1); 58 SIZ(lnsub1) = (n == 0 ? -1 : 1); 59 60 return; 61 } 62 63 TMP_MARK; 64 size = MPN_FIB2_SIZE (n); 65 f1p = TMP_ALLOC_LIMBS (size); 66 67 lp = MPZ_NEWALLOC (ln, size+1); 68 l1p = MPZ_NEWALLOC (lnsub1, size+1); 69 70 size = mpn_fib2_ui (l1p, f1p, n); 71 72 /* L[n] = F[n] + 2F[n-1] */ 73#if HAVE_NATIVE_mpn_addlsh1_n 74 c = mpn_addlsh1_n (lp, l1p, f1p, size); 75#else 76 c = mpn_lshift (lp, f1p, size, 1); 77 c += mpn_add_n (lp, lp, l1p, size); 78#endif 79 lp[size] = c; 80 SIZ(ln) = size + (c != 0); 81 82 /* L[n-1] = 2F[n] - F[n-1] */ 83#if HAVE_NATIVE_mpn_rsblsh1_n 84 c = mpn_rsblsh1_n (l1p, f1p, l1p, size); 85#else 86 c = mpn_lshift (l1p, l1p, size, 1); 87 c -= mpn_sub_n (l1p, l1p, f1p, size); 88#endif 89 ASSERT ((mp_limb_signed_t) c >= 0); 90 l1p[size] = c; 91 SIZ(lnsub1) = size + (c != 0); 92 93 TMP_FREE; 94} 95