lucnum2_ui.c
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上传日期:2022-08-06
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- /* mpz_lucnum2_ui -- calculate Lucas numbers.
- Copyright 2001, 2003, 2005 Free Software Foundation, Inc.
- This file is part of the GNU MP Library.
- The GNU MP Library is free software; you can redistribute it and/or modify
- it under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, or (at your
- option) any later version.
- The GNU MP Library is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include <stdio.h>
- #include "gmp.h"
- #include "gmp-impl.h"
- void
- mpz_lucnum2_ui (mpz_ptr ln, mpz_ptr lnsub1, unsigned long n)
- {
- mp_ptr lp, l1p, f1p;
- mp_size_t size;
- mp_limb_t c;
- TMP_DECL;
- ASSERT (ln != lnsub1);
- /* handle small n quickly, and hide the special case for L[-1]=-1 */
- if (n <= FIB_TABLE_LUCNUM_LIMIT)
- {
- mp_limb_t f = FIB_TABLE (n);
- mp_limb_t f1 = FIB_TABLE ((int) n - 1);
- /* L[n] = F[n] + 2F[n-1] */
- PTR(ln)[0] = f + 2*f1;
- SIZ(ln) = 1;
- /* L[n-1] = 2F[n] - F[n-1], but allow for L[-1]=-1 */
- PTR(lnsub1)[0] = (n == 0 ? 1 : 2*f - f1);
- SIZ(lnsub1) = (n == 0 ? -1 : 1);
- return;
- }
- TMP_MARK;
- size = MPN_FIB2_SIZE (n);
- f1p = TMP_ALLOC_LIMBS (size);
- MPZ_REALLOC (ln, size+1);
- MPZ_REALLOC (lnsub1, size+1);
- lp = PTR(ln);
- l1p = PTR(lnsub1);
- size = mpn_fib2_ui (l1p, f1p, n);
- /* L[n] = F[n] + 2F[n-1] */
- #if HAVE_NATIVE_mpn_addlsh1_n
- c = mpn_addlsh1_n (lp, l1p, f1p, size);
- #else
- c = mpn_lshift (lp, f1p, size, 1);
- c += mpn_add_n (lp, lp, l1p, size);
- #endif
- lp[size] = c;
- SIZ(ln) = size + (c != 0);
- /* L[n-1] = 2F[n] - F[n-1] */
- c = mpn_lshift (l1p, l1p, size, 1);
- c -= mpn_sub_n (l1p, l1p, f1p, size);
- ASSERT ((mp_limb_signed_t) c >= 0);
- l1p[size] = c;
- SIZ(lnsub1) = size + (c != 0);
- TMP_FREE;
- }